Atrial Standstill

Heart Disorder MONDO:0015281 Pathograph 21 Show in embeddings browser Heart Disorder Cardiac Arrhythmia

Atrial standstill is a rare rhythm disease defined by absent atrial electrical activity together with absent mechanical contraction. This entry models the primary or isolated disease represented by MONDO:0015281 and ORPHA:1344, including partial versus diffuse and transient versus persistent presentations. It does not collapse every secondary occurrence of atrial standstill into one disease: infiltrative, inflammatory, ischemic, toxic, metabolic, muscular-dystrophy, and broader inherited-cardiomyopathy contexts are etiologically distinct manifestations that must be evaluated separately. Consequences of the final common electromechanical failure include absent P waves, escape-rhythm bradycardia, syncope, pacing dependence, and thromboembolism.

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3
Inheritance
9
Pathophys.
9
Phenotypes
4
Hypotheses
2
Gaps
21
Pathograph
3
Genes
3
Medical Actions
2
Subtypes
4
Differentials
12
References
1
Deep Research
👪

Inheritance

3
Autosomal dominant inheritance HP:0000006
Dominant inheritance is established for the MYL4 p.E11K atrial cardiomyopathy family and is reported in some SCN5A families, often with incomplete penetrance or additional modifier effects.
Autosomal dominant inheritance
Show evidence (1 reference)
PMID:29080865 SUPPORT Human Clinical
"The inheritance pattern was very likely to be autosomal dominant"
The MYL4 family showed a dominant inheritance pattern.
Autosomal recessive inheritance HP:0000007
Biallelic SCN5A variants can cause severe early-onset atrial standstill; the original homozygous family had unaffected heterozygous relatives, and later synthesis includes both homozygous and compound-heterozygous cases.
Autosomal recessive inheritance
Show evidence (2 references)
PMID:29781517 SUPPORT Human Clinical
"A novel homozygous SCN5A mutation, p.V1340L, was identified in the proband and her sister."
The affected sisters carried homozygous SCN5A p.V1340L.
PMID:41280527 SUPPORT Human Clinical
"Genotype analysis revealed 21 patients with homozygous SCN5A variants (34%) and 40 with compound heterozygous variants (66%)."
The systematic review confirms both homozygous and compound-heterozygous SCN5A disease.
Digenic inheritance HP:0010984
A family-specific digenic model combines an SCN5A variant with regulatory GJA5/connexin-40 polymorphisms. This is not asserted as the inheritance mode for all atrial standstill.
Digenic inheritance
Show evidence (1 reference)
PMID:16188595 SUPPORT Human Clinical
"Incomplete penetrance observed in atrial standstill has been attributed in part to the digenic inheritance of polymorphisms in the atrial-specific gap junction connexin 40 (Cx40) in conjunction with an SCN5A mutation."
The study explicitly describes a digenic SCN5A/GJA5 inheritance model.
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Subtypes

2
Partial atrial standstill
Regional atrial electrical inactivity with residual excitable atrial tissue, sometimes limited to sites such as the coronary sinus.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"Atrial standstill is a rare clinical condition characterized by absence of electrical and mechanical atrial activity, and the spatial distribution of atrial lesion can be diffuse or partial."
Supports partial versus diffuse atrial standstill as a clinically recognized spatial distinction.
Diffuse atrial standstill
Widespread atrial electrical and mechanical inactivity, often with failure to capture the atria by pacing.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"Atrial standstill is a rare clinical condition characterized by absence of electrical and mechanical atrial activity, and the spatial distribution of atrial lesion can be diffuse or partial."
Supports diffuse atrial standstill as the extensive end of the spatial involvement spectrum.
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Mechanistic Hypotheses

4
SCN5A-Related Atrial Excitability Failure
scn5a_atrial_excitability_failure CANONICAL
Evidence balance 2 support
Pathogenic SCN5A loss-of-function reduces sodium-current availability and suppresses atrial action-potential initiation or propagation. This is the best-supported electrical route to primary atrial standstill, with human segregation, functional channel studies, a multicenter pediatric cohort, and a systematic review of biallelic SCN5A disease.
Pathograph links
SCN5A Sodium-Channel Loss of Function -> Atrial Electrical Silence DIRECT Reduced sodium-channel-dependent action-potential initiation prevents effective atrial depolarization.
Show evidence (2 references)
PMID:29781517 SUPPORT In Vitro
"CONCLUSIONS: A homozygous loss-of-function SCN5A mutation likely results in atrial standstill and sudden death due to suppression of initiation of action potential."
Functional channel data directly support the atrial-excitability mechanism.
PMID:36435694 SUPPORT Human Clinical
"Genetic testing identified SCN5A variants in 13 patients (65%). Analyses suggest SCN5A loss-of-function may be one mechanism driving AS."
A multicenter pediatric cohort independently supports SCN5A loss of function as a major mechanism.
MYL4-Related Progressive Atrial Cardiomyopathy
myl4_atrial_cardiomyopathy CANONICAL
Evidence balance 1 support
MYL4 loss of function disrupts atrial contractile, electrical, and structural integrity, producing a progressive atrial-selective cardiomyopathy that can culminate in standstill.
Pathograph links
MYL4 Loss of Function -> Loss of Atrial Mechanical Contraction DIRECT Loss of an atrial-selective sarcomeric light chain impairs atrial contraction.
Show evidence (1 reference)
PMID:29080865 SUPPORT Human Clinical
"The mutation cosegregated with atrial standstill (selected as the principal presenting trait) with a logarithm of the odds score of 5.3."
Human cosegregation strongly supports the MYL4 atrial-cardiomyopathy branch.
GJA5/Connexin-40 Conduction-Reserve Modifier
gja5_conduction_reserve_modifier EMERGING
Evidence balance 1 support
In two families, regulatory GJA5/connexin-40 genotypes accompanied SCN5A variants and were proposed to reduce atrial conduction reserve. The evidence supports a modifier or family-specific digenic contribution, not a universal requirement and not an independently established monogenic cause.
Pathograph links
Connexin 40 Modifier of Atrial Conduction Reserve -> Atrial Electrical Silence INDIRECT KNOWN INTERMEDIATES Reduced conduction reserve can increase susceptibility to atrial inexcitability when sodium-channel function is impaired. Intermediates: reduced atrial gap-junction conduction reserve; SCN5A sodium-channel dysfunction
Show evidence (1 reference)
PMID:12522116 SUPPORT Human Clinical
"The three living AS patients exclusively coinherited both the rare Cx40 genotype and the SCN5A-D1275N mutation."
The affected relatives uniquely carried both loci in this family.
MYL4 Autophagy-Fibrosis Mechanism
myl4_autophagy_fibrosis EMERGING
Evidence balance 1 support
MYL4 dysfunction may impair lysosomal mobility and autophagic flux, promoting atrial-myocyte injury and fibrosis. This mechanistic layer is supported by rat and cell experiments but has not yet been demonstrated in human atrial tissue or tested therapeutically in patients.
Pathograph links
MYL4 Loss of Function -> Atrial Cardiomyocyte Autophagic and Survival Dysfunction INDIRECT KNOWN INTERMEDIATES MYL4-dependent lysosomal and autophagic dysfunction is a model-supported route to atrial-myocyte injury. Intermediates: altered lysosomal mobility and acidification; impaired autophagic flux
Atrial Cardiomyocyte Autophagic and Survival Dysfunction -> Atrial Fibrosis and Low-Voltage Scar INDIRECT KNOWN INTERMEDIATES Chronic atrial-myocyte injury and profibrotic signaling promote fibrotic atrial remodeling in the MYL4 model. Intermediates: atrial cardiomyocyte injury and death; profibrotic signaling
Show evidence (1 reference)
PMID:36645977 SUPPORT Model Organism
"Rats subjected to knock-in of a pathogenic MYL4 mutant (p.E11K) developed fibrotic atrial cardiomyopathy."
The rat knock-in model supports an autophagy-fibrosis mechanism while leaving human translation unresolved.
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Discussions and Knowledge Gaps

2
Which pacing configuration and anticoagulation strategy best prevent thromboembolism, pacing-related ventricular dysfunction, and sudden events across partial, diffuse, monoallelic, and biallelic atrial standstill?
KNOWLEDGE GAP OPEN disc_atrial_standstill_management_evidence
Attached to
treatments#Permanent pacemaker implantation treatments#Coronary sinus atrial lead placement for partial atrial standstill treatments#Anticoagulant therapy for thromboembolic risk pathophysiology#Thromboembolic Risk from Atrial Stasis
Management evidence is a retrospective 20-patient pediatric cohort plus case reports. As of a ClinicalTrials.gov review on 2026-07-20, no study explicitly enrolled atrial standstill as a condition; the sole API match for the exact condition, NCT06166277, enrolled vasovagal syncope, Mobitz I AV block, and sinus pause and acquired the atrial-standstill label only through derived MeSH indexing. No disease-specific interventional trial was added.
Proposed experiments
Prospective multinational atrial standstill registry
exp_atrial_standstill_multinational_registry
Enroll primary and secondary cases with explicit etiologic classification, genotype, partial-versus-diffuse mapping, atrial capture status, pacing strategy, anticoagulant exposure, bleeding, thromboembolism, ventricular function, arrhythmias, and mortality using prespecified longitudinal endpoints.
Posed 2026-07-20T00:00:00Z
Show evidence (1 reference)
PMID:36435694 SUPPORT Human Clinical
"Studies to date have been limited."
The multicenter investigators explicitly identify the limited evidence base.
Does MYL4-dependent autophagic-flux failure operate in human atrial tissue, and can restoring MYL4 safely reverse established atrial fibrosis or electrical silence?
HUMAN MODEL MISMATCH OPEN disc_myl4_model_translation
Attached to
pathophysiology#MYL4 Loss of Function pathophysiology#Atrial Cardiomyocyte Autophagic and Survival Dysfunction pathophysiology#Atrial Fibrosis and Low-Voltage Scar
Knock-in rats and cultured cardiomyocytes support lysosomal/autophagic dysfunction and adenoviral MYL4 rescue, but no human atrial-tissue confirmation or clinical intervention establishes relevance, reversibility, dose, or safety in patients.
Proposed experiments
Human MYL4 atrial tissue and engineered-tissue validation
exp_myl4_human_atrial_validation
Compare atrial tissue or patient-derived atrial engineered tissues from pathogenic-MYL4 carriers and matched controls for autophagic flux, lysosomal function, myocyte survival, conduction, contraction, and fibrosis; test controlled MYL4 restoration with rescue and off-target criteria.
Posed 2026-07-20T00:00:00Z
Show evidence (1 reference)
PMID:36645977 SUPPORT Model Organism
"MYL4 protein overexpression attenuated atrial structural remodeling and autophagy dysfunction."
Rat gene-transfer rescue motivates translation while remaining preclinical.
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Pathophysiology

9
SCN5A Sodium-Channel Loss of Function
Loss-of-function SCN5A variants reduce atrial sodium current and impair initiation or propagation of the atrial cardiomyocyte action potential. This decreases atrial excitability and can produce progressive atrial standstill.
SCN5A-Related Atrial Excitability Failure
atrial cardiac myocyte CL:0002129 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves atrial cardiac myocyte, annotated with regular atrial cardiac myocyte (CL:0002129). CL:0002129 is a cell type from the Cell Ontology.
SCN5A hgnc:10593 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves SCN5A (hgnc:10593). hgnc:10593 is a gene from the HUGO Gene Nomenclature Committee.
cardiac muscle cell action potential GO:0086001 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cardiac muscle cell action potential (GO:0086001). GO:0086001 is a biological process from the Gene Ontology. ↓ DECREASED cardiac conduction GO:0061337 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cardiac conduction (GO:0061337). GO:0061337 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Atrial Electrical Silence Reduced sodium-channel-dependent action-potential initiation prevents effective atrial depolarization. SCN5A-Related Atrial Excitability Failure
Show evidence (2 references)
PMID:29781517 SUPPORT In Vitro
"CONCLUSIONS: A homozygous loss-of-function SCN5A mutation likely results in"
Functional channel evidence directly supports SCN5A loss of function as an upstream excitability mechanism for atrial standstill.
PMID:16188595 SUPPORT Human Clinical
"P waves on surface ECG, and his right atrium could not be captured by pacing."
This family study links an SCN5A variant to absent atrial activity and atrial inexcitability in a proband.
Connexin 40 Modifier of Atrial Conduction Reserve
GJA5-encoded connexin 40 polymorphisms are reported as possible modifiers in SCN5A-associated atrial standstill, reducing atrial conduction reserve and contributing to incomplete penetrance.
GJA5/Connexin-40 Conduction-Reserve Modifier
atrial cardiac myocyte CL:0002129 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves atrial cardiac myocyte, annotated with regular atrial cardiac myocyte (CL:0002129). CL:0002129 is a cell type from the Cell Ontology.
GJA5 hgnc:4279 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves GJA5 (hgnc:4279). hgnc:4279 is a gene from the HUGO Gene Nomenclature Committee.
cardiac conduction GO:0061337 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cardiac conduction (GO:0061337). GO:0061337 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Atrial Electrical Silence Reduced conduction reserve can increase susceptibility to atrial inexcitability when sodium-channel function is impaired. GJA5/Connexin-40 Conduction-Reserve Modifier
Show evidence (1 reference)
PMID:16188595 SUPPORT Human Clinical
"genetic factor that modifies the clinical manifestation of this inherited"
Supports connexin 40/GJA5 variation as a modifier rather than a standalone causative gene in the cited family.
MYL4 Loss of Function
Pathogenic MYL4 loss of function disrupts an atrial-selective myosin light chain required for contractile, electrical, and structural integrity. A p.E11K variant cosegregated with atrial standstill in a large dominant family, and engineered rats recapitulated progressive atrial dysfunction.
MYL4 Autophagy-Fibrosis Mechanism MYL4-Related Progressive Atrial Cardiomyopathy
atrial cardiac myocyte CL:0002129 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves atrial cardiac myocyte, annotated with regular atrial cardiac myocyte (CL:0002129). CL:0002129 is a cell type from the Cell Ontology.
MYL4 hgnc:7585 HUGO Gene Nomenclature Committee (hgnc) Relation: this pathophysiological event involves this gene This pathophysiological event involves MYL4 (hgnc:7585). hgnc:7585 is a gene from the HUGO Gene Nomenclature Committee.
sarcomere organization GO:0045214 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves abnormal sarcomere organization (GO:0045214). GO:0045214 is a biological process from the Gene Ontology. ⚠ ABNORMAL cardiac muscle contraction GO:0060048 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cardiac muscle contraction (GO:0060048). GO:0060048 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Loss of Atrial Mechanical Contraction Loss of an atrial-selective sarcomeric light chain impairs atrial contraction. MYL4-Related Progressive Atrial Cardiomyopathy
Atrial Cardiomyocyte Autophagic and Survival Dysfunction MYL4-dependent lysosomal and autophagic dysfunction is a model-supported route to atrial-myocyte injury. MYL4 Autophagy-Fibrosis Mechanism
Show evidence (2 references)
PMID:29080865 SUPPORT Human Clinical
"The mutation cosegregated with atrial standstill (selected as the principal presenting trait) with a logarithm of the odds score of 5.3."
Human cosegregation supports MYL4 loss of function as an upstream cause.
PMID:29080865 SUPPORT Model Organism
"Both MYL4 p.E11K knock-in rats and MYL4 knockout rats showed progressive atrial electrophysiological, contractile, and fibrotic abnormalities, similar to affected patients."
Engineered rats reproduce the electrical, mechanical, and structural atrial phenotype.
Atrial Cardiomyocyte Autophagic and Survival Dysfunction
In MYL4-mutant models, impaired autophagic flux, lysosomal dysfunction, and proapoptotic signaling injure atrial cardiomyocytes. This node is explicitly model-based; confirmation in human atrial tissue is lacking.
MYL4 Autophagy-Fibrosis Mechanism
atrial cardiac myocyte CL:0002129 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves atrial cardiac myocyte, annotated with regular atrial cardiac myocyte (CL:0002129). CL:0002129 is a cell type from the Cell Ontology.
autophagy GO:0006914 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased autophagy (GO:0006914). GO:0006914 is a biological process from the Gene Ontology. ↓ DECREASED apoptotic process GO:0006915 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased apoptotic process (GO:0006915). GO:0006915 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Atrial Fibrosis and Low-Voltage Scar Chronic atrial-myocyte injury and profibrotic signaling promote fibrotic atrial remodeling in the MYL4 model. MYL4 Autophagy-Fibrosis Mechanism
Show evidence (2 references)
PMID:36645977 SUPPORT Model Organism
"Next, we identified that dysfunctional MYL4 protein impairs autophagy flux in vitro and in vivo."
Rat and cellular experiments directly support impaired autophagic flux.
PMID:29080865 SUPPORT Model Organism
"Biochemical analyses of MYL4 p.E11K mutation rats showed activation of proapoptotic and profibrotic signaling, along with increased atrial-cardiomyocyte terminal deoxynucleotidyl transferase dUTP nick end labeling staining, suggesting enhanced apoptotic cell death"
The rat model supports atrial-myocyte apoptosis and profibrotic signaling.
Atrial Fibrosis and Low-Voltage Scar
In MYL4-related primary atrial cardiomyopathy and in several secondary disorders, atrial fibrosis and scar create a low-voltage substrate and reduce atrial excitability. A fibrotic final common pathway is plausible but is not required for SCN5A-mediated electrical standstill.
cardiac fibroblast CL:0002548 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves cardiac fibroblast, annotated with fibroblast of cardiac tissue (CL:0002548). CL:0002548 is a cell type from the Cell Ontology. atrial cardiac myocyte CL:0002129 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves atrial cardiac myocyte, annotated with regular atrial cardiac myocyte (CL:0002129). CL:0002129 is a cell type from the Cell Ontology.
extracellular matrix organization GO:0030198 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased extracellular matrix organization (GO:0030198). GO:0030198 is a biological process from the Gene Ontology. ↑ INCREASED cardiac conduction GO:0061337 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cardiac conduction (GO:0061337). GO:0061337 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Atrial Electrical Silence Scarred atrial myocardium loses recordable electrical activity and pacing capture.
Right atrial enlargement Progressive atrial structural remodeling can dilate the right atrium in advanced atrial standstill.
Left atrial enlargement Progressive atrial structural remodeling can dilate the left atrium in advanced atrial standstill.
Show evidence (3 references)
PMID:30546677 SUPPORT Human Clinical
"sick-sinus syndrome could be complicated in the case of diffuse atrial fibrosis."
Supports diffuse atrial fibrosis as a structural substrate for atrial standstill in an inflammatory cardiac disease context.
PMID:29387541 SUPPORT Human Clinical
"Voltage mapping showed significant right atrial scar"
Supports right atrial scar/low-voltage substrate in progressive atrial standstill.
PMID:29080865 SUPPORT Model Organism
"Both MYL4 p.E11K knock-in rats and MYL4 knockout rats showed progressive atrial electrophysiological, contractile, and fibrotic abnormalities, similar to affected patients."
The MYL4 models directly support progressive fibrotic atrial remodeling.
Atrial Electrical Silence
The final common electrophysiologic state is absence of atrial electrical activity, absent P waves, and failure to capture atrial tissue by pacing.
atrial cardiac myocyte CL:0002129 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves atrial cardiac myocyte, annotated with regular atrial cardiac myocyte (CL:0002129). CL:0002129 is a cell type from the Cell Ontology.
cardiac conduction GO:0061337 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cardiac conduction (GO:0061337). GO:0061337 is a biological process from the Gene Ontology. ↓ DECREASED
right cardiac atrium UBERON:0002078 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in right cardiac atrium (UBERON:0002078). UBERON:0002078 is an anatomical location from the Uberon multi-species anatomy ontology. left cardiac atrium UBERON:0002079 Uberon multi-species anatomy ontology (UBERON) Relation: this pathophysiological event occurs in this anatomical location This pathophysiological event occurs in left cardiac atrium (UBERON:0002079). UBERON:0002079 is an anatomical location from the Uberon multi-species anatomy ontology.
Downstream
Atrial standstill Electrical silence of atrial myocardium is the defining electrophysiologic component of atrial standstill.
Loss of Atrial Mechanical Contraction Absent atrial depolarization eliminates coordinated atrial contraction.
Escape Rhythm Bradycardia When atrial activity is absent, cardiac output depends on junctional or ventricular escape rhythms.
Show evidence (1 reference)
PMID:29387541 SUPPORT Human Clinical
"Atrial standstill (AS), a rare arrhythmogenic condition, is defined by (1) the absence of P waves in surface and intracavitary electrocardiograms (ECGs), (2) the absence of A waves in jugular venous pulse and right atrial pressure tracings, (3) the presence of a supraventricular type QRS..."
Provides a direct diagnostic definition of atrial electrical silence and atrial inexcitability.
Loss of Atrial Mechanical Contraction
Loss of atrial contraction abolishes Doppler A waves, reduces atrial contribution to ventricular filling, and promotes atrial blood stasis.
atrial cardiac myocyte CL:0002129 Cell Ontology (CL) Relation: this pathophysiological event involves this cell type This pathophysiological event involves atrial cardiac myocyte, annotated with regular atrial cardiac myocyte (CL:0002129). CL:0002129 is a cell type from the Cell Ontology.
cardiac muscle contraction GO:0060048 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased cardiac muscle contraction (GO:0060048). GO:0060048 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Thromboembolic Risk from Atrial Stasis Ineffective atrial contraction can promote stasis and thromboembolic stroke risk, especially in genetic cardiomyopathy contexts.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"No mechanical atrial activity was observed in a Doppler study of the mitral and tricuspid inflow regions"
Supports loss of mechanical atrial contraction as a core physiologic consequence of atrial standstill.
Thromboembolic Risk from Atrial Stasis
Absence of coordinated atrial contraction can promote atrial blood stasis, intracardiac thrombus formation, and systemic thromboembolism. Risk is not confined to EMD/LVNC: it was substantial in a pediatric primary-standstill cohort, especially when effective atrial pacing was not possible.
blood coagulation GO:0007596 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves increased blood coagulation (GO:0007596). GO:0007596 is a biological process from the Gene Ontology. ↑ INCREASED
Downstream
Thromboembolic stroke Increased thromboembolic risk can manifest clinically as ischemic stroke.
Show evidence (2 references)
PMID:32755394 SUPPORT Human Clinical
"probably due to the increased risk of thromboembolism attributable to both"
Supports thromboembolic risk as a mechanistic consequence of atrial standstill with LVNC in EMD-associated disease.
PMID:36435694 SUPPORT Human Clinical
"During a median follow-up of 6.9 years (IQR: 1.2-13.3 years), 7 (35%) had thromboembolic events."
A multicenter pediatric cohort directly quantifies thromboembolic events in primary atrial standstill.
Escape Rhythm Bradycardia
Junctional or ventricular escape rhythm can produce symptomatic bradycardia, pauses, presyncope, or syncope.
regulation of heart rate GO:0002027 Gene Ontology (GO) Relation: this pathophysiological event involves this biological process This pathophysiological event involves decreased regulation of heart rate (GO:0002027). GO:0002027 is a biological process from the Gene Ontology. ↓ DECREASED
Downstream
Bradycardia Dependence on slow escape rhythms manifests clinically as bradycardia.
Syncope and presyncope Slow escape rhythm or pauses can reduce cerebral perfusion enough to cause presyncope or syncope.
Show evidence (1 reference)
PMID:35425822 SUPPORT Human Clinical
"symptomatic bradycardia, which requires permanent pacemaker (PPM) implantation."
Supports symptomatic bradycardia as a common clinical manifestation and treatment driver in atrial standstill.
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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.
Pathograph: causal mechanism network for Atrial Standstill Interactive directed graph showing how pathophysiology mechanisms, phenotypes, genetic factors and variants, experimental models, environmental triggers, and treatments relate through causal and linked edges.
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Phenotypes

9
Cardiovascular 5
Bradycardia HP:0001662 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Bradycardia (HP:0001662). HP:0001662 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35425822 SUPPORT Human Clinical
"symptomatic bradycardia, which requires permanent pacemaker (PPM) implantation."
Supports symptomatic bradycardia as a typical manifestation.
Syncope and presyncope HP:0001279 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Syncope (HP:0001279). HP:0001279 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:29387541 SUPPORT Human Clinical
"An African American male patient presented with palpitations and syncope at the age of 12 years."
Supports syncope as a reported clinical manifestation.
PMID:31285994 SUPPORT Human Clinical
"This included a pause of 8.4 seconds, which was associated with presyncope."
Supports presyncope from long pauses in atrial standstill.
Ventricular tachycardia HP:0004756 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Ventricular tachycardia (HP:0004756). HP:0004756 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36435694 SUPPORT Human Clinical
"Arrhythmias included 16 (80%) with atrial/supraventricular arrhythmias and 8 (40%) with ventricular tachycardia, including 4 with cardiac arrests."
The multicenter pediatric cohort documents ventricular tachycardia as a non-defining but serious associated phenotype.
Cardiac arrest HP:0001695 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Cardiac arrest (HP:0001695). HP:0001695 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:36435694 SUPPORT Human Clinical
"Ventricular arrhythmias and cardiac arrest were more commonly seen in patients with biallelic SCN5A variants."
The cohort links cardiac arrest risk particularly to biallelic SCN5A disease.
Thromboembolic stroke HP:0001297 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Stroke (HP:0001297). HP:0001297 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:32755394 SUPPORT Human Clinical
"Notably, a strong family history of stroke observed in these families was"
Supports thromboembolic stroke risk from atrial standstill in EMD/LVNC families.
PMID:39669928 SUPPORT Human Clinical
"We present a case of HCN4 gene mutation presenting with atrial standstill and"
Supports stroke as a reported complication in a young patient with atrial standstill.
PMID:36435694 SUPPORT Human Clinical
"During a median follow-up of 6.9 years (IQR: 1.2-13.3 years), 7 (35%) had thromboembolic events."
The pediatric cohort establishes thromboembolism as a primary-standstill complication, although not every event was a stroke.
Other 4
Atrial standstill HP:0025478 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Atrial standstill (HP:0025478). HP:0025478 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:35425822 SUPPORT Human Clinical
"Atrial standstill (AS) is a rare condition defined by the lack of atrial"
Directly supports the defining atrial standstill phenotype.
Absent P wave HP:0033122 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Absent P wave (HP:0033122). HP:0033122 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:16188595 SUPPORT Human Clinical
"P waves on surface ECG, and his right atrium could not be captured by pacing."
Supports absent P waves as a direct ECG manifestation of atrial standstill.
Right atrial enlargement HP:0030718 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Right atrial enlargement (HP:0030718). HP:0030718 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"The right and left atria were markedly dilated on echocardiography"
Supports right atrial enlargement in a reported atrial standstill case.
Left atrial enlargement HP:0031295 Human Phenotype Ontology (HP) Relation: this clinical feature is this phenotype This clinical feature is Left atrial enlargement (HP:0031295). HP:0031295 is a phenotype from the Human Phenotype Ontology.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"The right and left atria were markedly dilated on echocardiography"
Supports left atrial enlargement in a reported atrial standstill case.
🧬

Genetic Associations

3
SCN5A (Established causative gene in familial atrial standstill)
Gene: SCN5A hgnc:10593 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is SCN5A (hgnc:10593). hgnc:10593 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (3 references)
PMID:29781517 SUPPORT Human Clinical
"RESULTS: A novel homozygous SCN5A mutation, p.V1340L, was identified in the"
Supports SCN5A as a familial atrial standstill gene.
PMID:16188595 SUPPORT Human Clinical
"The novel SCN5A mutation L212P was identified in the proband"
Supports an additional SCN5A variant associated with congenital atrial standstill.
PMID:41280527 SUPPORT Human Clinical
"Sinus node dysfunction was the most prevalent phenotype (35/54, 65%), often associated with atrial standstill (20/34, 59%)."
A 2025 systematic review establishes atrial standstill as a frequent component of severe biallelic SCN5A disease.
GJA5 (Modifier of SCN5A-associated atrial standstill)
Gene: GJA5 hgnc:4279 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is GJA5 (hgnc:4279). hgnc:4279 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: MODIFIER variant_origin: GERMLINE
Show evidence (2 references)
PMID:12522116 SUPPORT Human Clinical
"In this study, familial AS was associated with the concurrence of a cardiac sodium channel mutation and rare polymorphisms in the atrial-specific Cx40 gene."
The large-family study supports concurrence of SCN5A and GJA5 variation.
PMID:16188595 SUPPORT Human Clinical
"genetic factor that modifies the clinical manifestation of this inherited"
Supports GJA5/connexin 40 as a modifier of inherited atrial standstill.
MYL4 (Established causative gene for progressive heritable atrial cardiomyopathy with atrial standstill)
Gene: MYL4 hgnc:7585 HUGO Gene Nomenclature Committee (hgnc) Relation: this disease-associated gene is this gene This disease-associated gene is MYL4 (hgnc:7585). hgnc:7585 is a gene from the HUGO Gene Nomenclature Committee. relationship_type: CAUSATIVE variant_origin: GERMLINE
Show evidence (2 references)
PMID:29080865 SUPPORT Human Clinical
"The mutation cosegregated with atrial standstill (selected as the principal presenting trait) with a logarithm of the odds score of 5.3."
Strong human cosegregation supports MYL4 as a primary atrial-standstill gene.
PMID:29080865 SUPPORT Model Organism
"The phenotype of rats with MYL4 mutation knock-in confirmed the causative role of the mutation."
The knock-in model functionally corroborates the human genetic association.
💊

Medical Actions

3
Permanent pacemaker implantation
Action: pacemaker implantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is pacemaker implantation, annotated with Pacemaker Placement (NCIT:C80434). NCIT:C80434 is a clinical intervention from the NCI Thesaurus. Ontology label: Pacemaker Placement NCIT:C80434
Persistent or symptomatic atrial standstill often requires permanent pacing, commonly ventricular pacing when atrial capture is absent. Physiologic ventricular pacing such as left bundle branch area pacing has been reported to reduce pacing dyssynchrony risk in selected cases.
Mechanism Target:
MODULATES Escape Rhythm Bradycardia — Permanent pacing stabilizes ventricular rate when escape rhythm bradycardia causes symptoms or pacing dependence.
Target Phenotypes: Bradycardia HP:0001662 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Bradycardia (HP:0001662). HP:0001662 is a phenotype from the Human Phenotype Ontology.
Show evidence (3 references)
PMID:35425822 SUPPORT Human Clinical
"symptomatic bradycardia, which requires permanent pacemaker (PPM) implantation."
Supports pacemaker implantation for symptomatic bradycardia in atrial standstill.
PMID:29387541 SUPPORT Human Clinical
"lack of right atrial sensing or capture with transvenous atrial lead placement attempts, so a single-chamber ventricular pacemaker was placed."
Supports ventricular pacemaker placement when atrial sensing/capture fails.
PMID:36435694 SUPPORT Human Clinical
"Pacemakers were implanted in 18 (90%). Although atrial leads were attempted in 15, only 4 achieved pacing at implantation."
The multicenter pediatric cohort documents frequent device need and the difficulty of atrial capture.
Coronary sinus atrial lead placement for partial atrial standstill
Action: pacemaker implantationNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is pacemaker implantation, annotated with Pacemaker Placement (NCIT:C80434). NCIT:C80434 is a clinical intervention from the NCI Thesaurus. Ontology label: Pacemaker Placement NCIT:C80434
In partial atrial standstill, EP mapping may identify residual excitable tissue in the coronary sinus, allowing atrial lead placement and atrioventricular synchronous pacing.
Mechanism Target:
MODULATES Atrial Electrical Silence — Coronary sinus lead placement can use residual atrial electrical activity when diffuse right atrial capture is not possible.
Show evidence (2 references)
PMID:31285994 SUPPORT Human Clinical
"Pacemaker implantation was necessary owing to symptomatic sick sinus syndrome."
Supports pacemaker implantation as required in the reported partial atrial standstill case.
PMID:31285994 SUPPORT Human Clinical
"We succeeded in placing the atrial lead with the initial attempt, and we placed the lead of the pacemaker proximally inside the CS"
Supports coronary sinus atrial lead placement when residual activity is mapped there.
Anticoagulant therapy for thromboembolic risk
Action: anticoagulant agent therapyNCI Thesaurus (NCIT) Relation: this treatment is this clinical intervention This treatment is anticoagulant agent therapy, annotated with Anticoagulation Therapy (NCIT:C63341). NCIT:C63341 is a clinical intervention from the NCI Thesaurus. Ontology label: Anticoagulation Therapy NCIT:C63341
Anticoagulation is used to reduce thromboembolism from atrial mechanical standstill. The strongest disease-specific evidence is a retrospective pediatric cohort in which events clustered among patients without effective atrial pacing; there is no randomized atrial-standstill trial defining agent, threshold, or duration.
Mechanism Target:
INHIBITS Thromboembolic Risk from Atrial Stasis — Anticoagulant therapy is intended to reduce thromboembolic risk arising from atrial paralysis and associated cardiomyopathy.
Target Phenotypes: Stroke HP:0001297 Human Phenotype Ontology (HP) Relation: this treatment targets this phenotype This treatment targets Stroke (HP:0001297). HP:0001297 is a phenotype from the Human Phenotype Ontology.
Show evidence (2 references)
PMID:36435694 SUPPORT Human Clinical
"Patients without the capacity for atrial pacing are at risk for thromboembolic events and warrant anticoagulation."
The multicenter cohort directly recommends anticoagulation for patients without effective atrial pacing; this remains observational evidence.
PMID:36435694 SUPPORT Human Clinical
"Of these, none had atrial pacing, 6 were not on anticoagulation, and 1 was on aspirin."
Event clustering supports the rationale but does not estimate comparative anticoagulant efficacy or establish a treatment threshold.
🔬

Diagnosis

5
Electrocardiography for absent P waves and escape rhythm
Surface ECG is the first-line diagnostic test, showing absent P waves and a junctional or ventricular escape rhythm rather than organized atrial activation. Absent P waves alone are not specific and must be paired with evidence of absent atrial mechanical activity and, when needed, atrial inexcitability.
electrocardiography NCIT:C38053 NCI Thesaurus (NCIT)
Results: Absent P waves with bradycardic escape rhythm support atrial standstill.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"The absence of P waves and bradycardia, along with a wide QRS complex, are seen on the electrocardiogram (ECG)."
Supports ECG recognition of absent P waves and bradycardia.
Echocardiography for absent atrial contraction
Doppler echocardiography assesses mechanical atrial activity and can show loss of A waves or atrial enlargement.
echocardiography NCIT:C16525 NCI Thesaurus (NCIT)
Results: Absent transmitral or transtricuspid A waves support loss of atrial mechanical contraction.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"No mechanical atrial activity was observed in a Doppler study of the mitral and tricuspid inflow regions"
Supports Doppler echocardiography as a diagnostic method for atrial mechanical standstill.
Electrophysiology study and mapping
Electrophysiology study confirms atrial inexcitability and identifies any residual viable atrial myocardium for potential atrial lead placement.
clinical cardiac electrophysiologist evaluation NCIT:C80414 NCI Thesaurus (NCIT)
Results: Failure to capture the atria and low-voltage or scarred regions confirm atrial electrical standstill.
Show evidence (2 references)
PMID:31285994 SUPPORT Human Clinical
"In atrial standstill when pacemaker implantations are thought to be necessary, evaluation by electrophysiological study should be considered before implantation."
Supports EP study before pacing when atrial standstill is suspected.
PMID:31285994 SUPPORT Human Clinical
"Only inside the CS did atrial electrical activities remain."
Supports mapping residual viable atrial tissue, including coronary sinus activity, before device planning.
Cardiac magnetic resonance imaging for fibrosis and cardiomyopathy assessment
Cardiac MRI can assess atrial and ventricular morphology, function, and delayed enhancement when a broader structural, inflammatory, infiltrative, or genetic cardiomyopathy is a concern. A normal MRI does not exclude the electrical diagnosis.
magnetic resonance imaging procedure NCIT:C16809 NCI Thesaurus (NCIT)
Results: Cardiac MRI may identify or help exclude associated cardiomyopathy; normal ventricular morphology and absent delayed enhancement do not exclude atrial standstill.
Show evidence (1 reference)
PMID:29387541 SUPPORT Human Clinical
"Cardiac magnetic resonance imaging showed normal morphology, function, and no delayed myocardial enhancement."
Supports cardiac MRI as part of the diagnostic workup to evaluate cardiac structure, function, and delayed enhancement.
Genetic testing for inherited atrial standstill
Genetic testing is indicated when familial, early-onset, progressive, or syndromic atrial standstill suggests inherited channelopathy or cardiomyopathy.
genetic testing NCIT:C15709 NCI Thesaurus (NCIT)
Results: Pathogenic SCN5A or MYL4 variants can support a primary inherited diagnosis; GJA5 findings require modifier-level interpretation, and broader panels can identify distinct cardiomyopathy syndromes.
Show evidence (2 references)
PMID:16188595 SUPPORT Human Clinical
"underwent genetic screening of SCN5A and atrial-specific genes including Cx40."
Supports genetic testing of SCN5A and atrial conduction genes in familial or apparently sporadic atrial standstill.
PMID:36435694 SUPPORT Human Clinical
"Genetic testing identified SCN5A variants in 13 patients (65%)."
The multicenter cohort supports a high diagnostic yield for SCN5A testing in selected pediatric primary cases.
🔀

Differential Diagnoses

4

Conditions with similar clinical presentations that must be differentiated from Atrial Standstill:

Secondary or acquired atrial standstill
Overlapping Features Atrial electrical and mechanical silence can be induced by hypoxia, myocardial infarction, amyloidosis, muscular dystrophy, inflammatory atrial disease, and quinidine or digitalis toxicity. These cases share the final phenotype but do not establish the primary isolated disease modeled here.
Distinguishing Features
  • A temporally related systemic, infiltrative, inflammatory, ischemic, metabolic, or drug exposure favors secondary standstill.
  • Reversibility after correction of the cause favors a transient secondary form.
  • Family history and pathogenic SCN5A or MYL4 variation favor primary inherited disease.
Show evidence (1 reference)
PMID:31285994 SUPPORT Human Clinical
"Previous reports showed that AS could be induced by various conditions, including hypoxia, muscular dystrophia, amyloidosis, myocardial infarction, and toxicity from quinidine or digitalis."
The review portion of the case report identifies recognized secondary contexts.
Broader inherited atrial or ventricular cardiomyopathy
Overlapping Features EMD/LMNA nuclear-envelope disease, NPPA atrial dilated cardiomyopathy, RYR2 exon-3 deletion disease, and rare TAF1A or HCN4 reports can include atrial standstill as one manifestation. They should be represented under their broader gene-specific disease identities unless evidence establishes a primary isolated-standstill relationship.
Distinguishing Features
  • Left ventricular noncompaction, ventricular dilation or fibrosis, skeletal myopathy, contractures, or a broad conduction/ventricular-arrhythmia phenotype favors a wider cardiomyopathy syndrome.
  • A gene-specific diagnosis outside SCN5A or MYL4 should not be promoted to primary isolated atrial standstill from a single case alone.
Show evidence (1 reference)
PMID:32755394 SUPPORT Human Clinical
"Cardiac emerinopathy is a novel nonsyndromic X-linked progressive atrial standstill associated with LVNC and increased risk of thromboembolism."
EMD-associated standstill is explicitly part of a distinct X-linked cardiac emerinopathy with LVNC.
Familial sick sinus syndrome MONDO:0012061
Overlapping Features Sinus-node dysfunction can cause pauses, bradycardia, and absent P waves without diffuse loss of atrial myocardium.
Distinguishing Features
  • Preserved atrial electrograms, atrial capture, or mechanical A waves argue against complete atrial standstill.
  • Electroanatomic mapping can distinguish sinus-node failure from regional or diffuse atrial inexcitability.
Atrial fibrillation MONDO:0004981
Overlapping Features Fine atrial fibrillation can obscure discrete P waves and abolish effective atrial contraction, but atrial electrical activity remains disorganized rather than absent.
Distinguishing Features
  • Fibrillatory surface or intracardiac activity favors atrial fibrillation.
  • Complete absence of atrial electrograms and failure of high-output atrial capture favor atrial standstill.
{ }

Source YAML

click to show 
name: Atrial Standstill
creation_date: "2026-05-06T17:25:39Z"
category: Heart Disorder
parents:
- Heart Disorder
- Cardiac Arrhythmia
disease_term:
  preferred_term: atrial standstill
  term:
    id: MONDO:0015281
    label: atrial standstill
description: >-
  Atrial standstill is a rare rhythm disease defined by absent atrial electrical
  activity together with absent mechanical contraction. This entry models the
  primary or isolated disease represented by MONDO:0015281 and ORPHA:1344,
  including partial versus diffuse and transient versus persistent
  presentations. It does not collapse every secondary occurrence of atrial
  standstill into one disease: infiltrative, inflammatory, ischemic, toxic,
  metabolic, muscular-dystrophy, and broader inherited-cardiomyopathy contexts
  are etiologically distinct manifestations that must be evaluated separately.
  Consequences of the final common electromechanical failure include absent P
  waves, escape-rhythm bradycardia, syncope, pacing dependence, and
  thromboembolism.
synonyms:
- AS
- Silent atrium
- Isolated atrial standstill
- Isolated atrial cardiomyopathy with heart block
- Persistent atrial standstill
- Permanent atrial standstill
- Partial atrial standstill
has_subtypes:
- name: Partial
  display_name: Partial atrial standstill
  description: >-
    Regional atrial electrical inactivity with residual excitable atrial tissue,
    sometimes limited to sites such as the coronary sinus.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atrial standstill is a rare clinical condition characterized by absence of electrical and mechanical atrial activity, and the spatial distribution of atrial lesion can be diffuse or partial."
    explanation: >-
      Supports partial versus diffuse atrial standstill as a clinically
      recognized spatial distinction.
- name: Diffuse
  display_name: Diffuse atrial standstill
  description: >-
    Widespread atrial electrical and mechanical inactivity, often with failure
    to capture the atria by pacing.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atrial standstill is a rare clinical condition characterized by absence of electrical and mechanical atrial activity, and the spatial distribution of atrial lesion can be diffuse or partial."
    explanation: >-
      Supports diffuse atrial standstill as the extensive end of the spatial
      involvement spectrum.
mechanistic_hypotheses:
- hypothesis_group_id: scn5a_atrial_excitability_failure
  hypothesis_label: SCN5A-Related Atrial Excitability Failure
  status: CANONICAL
  description: >-
    Pathogenic SCN5A loss-of-function reduces sodium-current availability and
    suppresses atrial action-potential initiation or propagation. This is the
    best-supported electrical route to primary atrial standstill, with human
    segregation, functional channel studies, a multicenter pediatric cohort,
    and a systematic review of biallelic SCN5A disease.
  evidence:
  - reference: PMID:29781517
    reference_title: A homozygous SCN5A mutation associated with atrial standstill and sudden death.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "CONCLUSIONS: A homozygous loss-of-function SCN5A mutation likely results in atrial standstill and sudden death due to suppression of initiation of action potential."
    explanation: Functional channel data directly support the atrial-excitability mechanism.
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genetic testing identified SCN5A variants in 13 patients (65%). Analyses suggest SCN5A loss-of-function may be one mechanism driving AS."
    explanation: A multicenter pediatric cohort independently supports SCN5A loss of function as a major mechanism.
- hypothesis_group_id: myl4_atrial_cardiomyopathy
  hypothesis_label: MYL4-Related Progressive Atrial Cardiomyopathy
  status: CANONICAL
  description: >-
    MYL4 loss of function disrupts atrial contractile, electrical, and
    structural integrity, producing a progressive atrial-selective
    cardiomyopathy that can culminate in standstill.
  evidence:
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mutation cosegregated with atrial standstill (selected as the principal presenting trait) with a logarithm of the odds score of 5.3."
    explanation: Human cosegregation strongly supports the MYL4 atrial-cardiomyopathy branch.
- hypothesis_group_id: gja5_conduction_reserve_modifier
  hypothesis_label: GJA5/Connexin-40 Conduction-Reserve Modifier
  status: EMERGING
  description: >-
    In two families, regulatory GJA5/connexin-40 genotypes accompanied SCN5A
    variants and were proposed to reduce atrial conduction reserve. The evidence
    supports a modifier or family-specific digenic contribution, not a universal
    requirement and not an independently established monogenic cause.
  evidence:
  - reference: PMID:12522116
    reference_title: A cardiac sodium channel mutation cosegregates with a rare connexin40 genotype in familial atrial standstill.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The three living AS patients exclusively coinherited both the rare Cx40 genotype and the SCN5A-D1275N mutation."
    explanation: The affected relatives uniquely carried both loci in this family.
- hypothesis_group_id: myl4_autophagy_fibrosis
  hypothesis_label: MYL4 Autophagy-Fibrosis Mechanism
  status: EMERGING
  description: >-
    MYL4 dysfunction may impair lysosomal mobility and autophagic flux, promoting
    atrial-myocyte injury and fibrosis. This mechanistic layer is supported by
    rat and cell experiments but has not yet been demonstrated in human atrial
    tissue or tested therapeutically in patients.
  evidence:
  - reference: PMID:36645977
    reference_title: Myosin light-chain 4 gene-transfer attenuates atrial fibrosis while correcting autophagic flux dysregulation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Rats subjected to knock-in of a pathogenic MYL4 mutant (p.E11K) developed fibrotic atrial cardiomyopathy."
    explanation: The rat knock-in model supports an autophagy-fibrosis mechanism while leaving human translation unresolved.
pathophysiology:
- name: SCN5A Sodium-Channel Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Loss-of-function SCN5A variants reduce atrial sodium current and impair
    initiation or propagation of the atrial cardiomyocyte action potential. This
    decreases atrial excitability and can produce progressive atrial standstill.
  genes:
  - preferred_term: SCN5A
    term:
      id: hgnc:10593
      label: SCN5A
  cell_types:
  - preferred_term: atrial cardiac myocyte
    term:
      id: CL:0002129
      label: regular atrial cardiac myocyte
  biological_processes:
  - preferred_term: cardiac muscle cell action potential
    term:
      id: GO:0086001
      label: cardiac muscle cell action potential
    modifier: DECREASED
  - preferred_term: cardiac conduction
    term:
      id: GO:0061337
      label: cardiac conduction
    modifier: DECREASED
  evidence:
  - reference: PMID:29781517
    reference_title: A homozygous SCN5A mutation associated with atrial standstill and sudden death.
    supports: SUPPORT
    evidence_source: IN_VITRO
    snippet: "CONCLUSIONS: A homozygous loss-of-function SCN5A mutation likely results in"
    explanation: >-
      Functional channel evidence directly supports SCN5A loss of function as
      an upstream excitability mechanism for atrial standstill.
  - reference: PMID:16188595
    reference_title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P waves on surface ECG, and his right atrium could not be captured by pacing."
    explanation: >-
      This family study links an SCN5A variant to absent atrial activity and
      atrial inexcitability in a proband.
  downstream:
  - target: Atrial Electrical Silence
    causal_link_type: DIRECT
    hypothesis_groups:
    - scn5a_atrial_excitability_failure
    description: >-
      Reduced sodium-channel-dependent action-potential initiation prevents
      effective atrial depolarization.
- name: Connexin 40 Modifier of Atrial Conduction Reserve
  biological_scale: CELLULAR
  description: >-
    GJA5-encoded connexin 40 polymorphisms are reported as possible modifiers in
    SCN5A-associated atrial standstill, reducing atrial conduction reserve and
    contributing to incomplete penetrance.
  genes:
  - preferred_term: GJA5
    term:
      id: hgnc:4279
      label: GJA5
  cell_types:
  - preferred_term: atrial cardiac myocyte
    term:
      id: CL:0002129
      label: regular atrial cardiac myocyte
  biological_processes:
  - preferred_term: cardiac conduction
    term:
      id: GO:0061337
      label: cardiac conduction
    modifier: DECREASED
  evidence:
  - reference: PMID:16188595
    reference_title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "genetic factor that modifies the clinical manifestation of this inherited"
    explanation: >-
      Supports connexin 40/GJA5 variation as a modifier rather than a standalone
      causative gene in the cited family.
  downstream:
  - target: Atrial Electrical Silence
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - gja5_conduction_reserve_modifier
    intermediate_mechanisms:
    - reduced atrial gap-junction conduction reserve
    - SCN5A sodium-channel dysfunction
    description: >-
      Reduced conduction reserve can increase susceptibility to atrial
      inexcitability when sodium-channel function is impaired.
- name: MYL4 Loss of Function
  biological_scale: MOLECULAR
  description: >-
    Pathogenic MYL4 loss of function disrupts an atrial-selective myosin light
    chain required for contractile, electrical, and structural integrity. A
    p.E11K variant cosegregated with atrial standstill in a large dominant
    family, and engineered rats recapitulated progressive atrial dysfunction.
  genes:
  - preferred_term: MYL4
    term:
      id: hgnc:7585
      label: MYL4
  cell_types:
  - preferred_term: atrial cardiac myocyte
    term:
      id: CL:0002129
      label: regular atrial cardiac myocyte
  biological_processes:
  - preferred_term: sarcomere organization
    term:
      id: GO:0045214
      label: sarcomere organization
    modifier: ABNORMAL
  - preferred_term: cardiac muscle contraction
    term:
      id: GO:0060048
      label: cardiac muscle contraction
    modifier: DECREASED
  evidence:
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mutation cosegregated with atrial standstill (selected as the principal presenting trait) with a logarithm of the odds score of 5.3."
    explanation: Human cosegregation supports MYL4 loss of function as an upstream cause.
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Both MYL4 p.E11K knock-in rats and MYL4 knockout rats showed progressive atrial electrophysiological, contractile, and fibrotic abnormalities, similar to affected patients."
    explanation: Engineered rats reproduce the electrical, mechanical, and structural atrial phenotype.
  downstream:
  - target: Loss of Atrial Mechanical Contraction
    causal_link_type: DIRECT
    hypothesis_groups:
    - myl4_atrial_cardiomyopathy
    description: >-
      Loss of an atrial-selective sarcomeric light chain impairs atrial
      contraction.
  - target: Atrial Cardiomyocyte Autophagic and Survival Dysfunction
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - myl4_autophagy_fibrosis
    intermediate_mechanisms:
    - altered lysosomal mobility and acidification
    - impaired autophagic flux
    description: >-
      MYL4-dependent lysosomal and autophagic dysfunction is a model-supported
      route to atrial-myocyte injury.
- name: Atrial Cardiomyocyte Autophagic and Survival Dysfunction
  biological_scale: CELLULAR
  description: >-
    In MYL4-mutant models, impaired autophagic flux, lysosomal dysfunction, and
    proapoptotic signaling injure atrial cardiomyocytes. This node is explicitly
    model-based; confirmation in human atrial tissue is lacking.
  cell_types:
  - preferred_term: atrial cardiac myocyte
    term:
      id: CL:0002129
      label: regular atrial cardiac myocyte
  biological_processes:
  - preferred_term: autophagy
    term:
      id: GO:0006914
      label: autophagy
    modifier: DECREASED
  - preferred_term: apoptotic process
    term:
      id: GO:0006915
      label: apoptotic process
    modifier: INCREASED
  evidence:
  - reference: PMID:36645977
    reference_title: Myosin light-chain 4 gene-transfer attenuates atrial fibrosis while correcting autophagic flux dysregulation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Next, we identified that dysfunctional MYL4 protein impairs autophagy flux in vitro and in vivo."
    explanation: Rat and cellular experiments directly support impaired autophagic flux.
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Biochemical analyses of MYL4 p.E11K mutation rats showed activation of proapoptotic and profibrotic signaling, along with increased atrial-cardiomyocyte terminal deoxynucleotidyl transferase dUTP nick end labeling staining, suggesting enhanced apoptotic cell death"
    explanation: The rat model supports atrial-myocyte apoptosis and profibrotic signaling.
  downstream:
  - target: Atrial Fibrosis and Low-Voltage Scar
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    hypothesis_groups:
    - myl4_autophagy_fibrosis
    intermediate_mechanisms:
    - atrial cardiomyocyte injury and death
    - profibrotic signaling
    description: >-
      Chronic atrial-myocyte injury and profibrotic signaling promote fibrotic
      atrial remodeling in the MYL4 model.
- name: Atrial Fibrosis and Low-Voltage Scar
  biological_scale: TISSUE
  description: >-
    In MYL4-related primary atrial cardiomyopathy and in several secondary
    disorders, atrial fibrosis and scar create a low-voltage substrate and
    reduce atrial excitability. A fibrotic final common pathway is plausible but
    is not required for SCN5A-mediated electrical standstill.
  cell_types:
  - preferred_term: cardiac fibroblast
    term:
      id: CL:0002548
      label: fibroblast of cardiac tissue
  - preferred_term: atrial cardiac myocyte
    term:
      id: CL:0002129
      label: regular atrial cardiac myocyte
  biological_processes:
  - preferred_term: extracellular matrix organization
    term:
      id: GO:0030198
      label: extracellular matrix organization
    modifier: INCREASED
  - preferred_term: cardiac conduction
    term:
      id: GO:0061337
      label: cardiac conduction
    modifier: DECREASED
  evidence:
  - reference: PMID:30546677
    reference_title: Atrial standstill in suspected isolated cardiac sarcoidosis.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "sick-sinus syndrome could be complicated in the case of diffuse atrial fibrosis."
    explanation: >-
      Supports diffuse atrial fibrosis as a structural substrate for atrial
      standstill in an inflammatory cardiac disease context.
  - reference: PMID:29387541
    reference_title: Atrial standstill in a pediatric patient with associated caveolin-3 mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Voltage mapping showed significant right atrial scar"
    explanation: >-
      Supports right atrial scar/low-voltage substrate in progressive atrial
      standstill.
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "Both MYL4 p.E11K knock-in rats and MYL4 knockout rats showed progressive atrial electrophysiological, contractile, and fibrotic abnormalities, similar to affected patients."
    explanation: The MYL4 models directly support progressive fibrotic atrial remodeling.
  downstream:
  - target: Atrial Electrical Silence
    causal_link_type: DIRECT
    description: >-
      Scarred atrial myocardium loses recordable electrical activity and pacing
      capture.
  - target: Right atrial enlargement
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - atrial structural remodeling
    - atrial dilation
    description: >-
      Progressive atrial structural remodeling can dilate the right atrium in
      advanced atrial standstill.
  - target: Left atrial enlargement
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - atrial structural remodeling
    - atrial dilation
    description: >-
      Progressive atrial structural remodeling can dilate the left atrium in
      advanced atrial standstill.
- name: Atrial Electrical Silence
  biological_scale: TISSUE
  description: >-
    The final common electrophysiologic state is absence of atrial electrical
    activity, absent P waves, and failure to capture atrial tissue by pacing.
  cell_types:
  - preferred_term: atrial cardiac myocyte
    term:
      id: CL:0002129
      label: regular atrial cardiac myocyte
  locations:
  - preferred_term: right cardiac atrium
    term:
      id: UBERON:0002078
      label: right cardiac atrium
  - preferred_term: left cardiac atrium
    term:
      id: UBERON:0002079
      label: left cardiac atrium
  biological_processes:
  - preferred_term: cardiac conduction
    term:
      id: GO:0061337
      label: cardiac conduction
    modifier: DECREASED
  evidence:
  - reference: PMID:29387541
    reference_title: Atrial standstill in a pediatric patient with associated caveolin-3 mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atrial standstill (AS), a rare arrhythmogenic condition, is defined by (1) the absence of P waves in surface and intracavitary electrocardiograms (ECGs), (2) the absence of A waves in jugular venous pulse and right atrial pressure tracings, (3) the presence of a supraventricular type QRS complex, (4) the immobility of the atria on fluoroscopy, and (5) the inability to stimulate the atria electrically."
    explanation: >-
      Provides a direct diagnostic definition of atrial electrical silence and
      atrial inexcitability.
  downstream:
  - target: Atrial standstill
    causal_link_type: DIRECT
    description: >-
      Electrical silence of atrial myocardium is the defining electrophysiologic
      component of atrial standstill.
  - target: Loss of Atrial Mechanical Contraction
    causal_link_type: DIRECT
    description: >-
      Absent atrial depolarization eliminates coordinated atrial contraction.
  - target: Escape Rhythm Bradycardia
    causal_link_type: DIRECT
    description: >-
      When atrial activity is absent, cardiac output depends on junctional or
      ventricular escape rhythms.
- name: Loss of Atrial Mechanical Contraction
  biological_scale: TISSUE
  description: >-
    Loss of atrial contraction abolishes Doppler A waves, reduces atrial
    contribution to ventricular filling, and promotes atrial blood stasis.
  cell_types:
  - preferred_term: atrial cardiac myocyte
    term:
      id: CL:0002129
      label: regular atrial cardiac myocyte
  biological_processes:
  - preferred_term: cardiac muscle contraction
    term:
      id: GO:0060048
      label: cardiac muscle contraction
    modifier: DECREASED
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No mechanical atrial activity was observed in a Doppler study of the mitral and tricuspid inflow regions"
    explanation: >-
      Supports loss of mechanical atrial contraction as a core physiologic
      consequence of atrial standstill.
  downstream:
  - target: Thromboembolic Risk from Atrial Stasis
    causal_link_type: DIRECT
    description: >-
      Ineffective atrial contraction can promote stasis and thromboembolic
      stroke risk, especially in genetic cardiomyopathy contexts.
- name: Thromboembolic Risk from Atrial Stasis
  biological_scale: ORGANISM
  description: >-
    Absence of coordinated atrial contraction can promote atrial blood stasis,
    intracardiac thrombus formation, and systemic thromboembolism. Risk is not
    confined to EMD/LVNC: it was substantial in a pediatric primary-standstill
    cohort, especially when effective atrial pacing was not possible.
  biological_processes:
  - preferred_term: blood coagulation
    term:
      id: GO:0007596
      label: blood coagulation
    modifier: INCREASED
  evidence:
  - reference: PMID:32755394
    reference_title: "Cardiac Emerinopathy: A Nonsyndromic Nuclear Envelopathy With Increased Risk of Thromboembolic Stroke Due to Progressive Atrial Standstill and Left Ventricular Noncompaction."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "probably due to the increased risk of thromboembolism attributable to both"
    explanation: >-
      Supports thromboembolic risk as a mechanistic consequence of atrial
      standstill with LVNC in EMD-associated disease.
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "During a median follow-up of 6.9 years (IQR: 1.2-13.3 years), 7 (35%) had thromboembolic events."
    explanation: A multicenter pediatric cohort directly quantifies thromboembolic events in primary atrial standstill.
  downstream:
  - target: Thromboembolic stroke
    causal_link_type: DIRECT
    description: >-
      Increased thromboembolic risk can manifest clinically as ischemic stroke.
- name: Escape Rhythm Bradycardia
  biological_scale: ORGANISM
  description: >-
    Junctional or ventricular escape rhythm can produce symptomatic bradycardia,
    pauses, presyncope, or syncope.
  biological_processes:
  - preferred_term: regulation of heart rate
    term:
      id: GO:0002027
      label: regulation of heart rate
    modifier: DECREASED
  evidence:
  - reference: PMID:35425822
    reference_title: "Left Bundle Branch Area Pacing in a Giant Atrium With Atrial Standstill: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "symptomatic bradycardia, which requires permanent pacemaker (PPM) implantation."
    explanation: >-
      Supports symptomatic bradycardia as a common clinical manifestation and
      treatment driver in atrial standstill.
  downstream:
  - target: Bradycardia
    causal_link_type: DIRECT
    description: >-
      Dependence on slow escape rhythms manifests clinically as bradycardia.
  - target: Syncope and presyncope
    causal_link_type: INDIRECT_KNOWN_INTERMEDIATES
    intermediate_mechanisms:
    - symptomatic bradycardia
    - long pauses
    - transient cerebral hypoperfusion
    description: >-
      Slow escape rhythm or pauses can reduce cerebral perfusion enough to cause
      presyncope or syncope.
phenotypes:
- name: Atrial standstill
  category: Cardiovascular
  diagnostic: true
  phenotype_term:
    preferred_term: Atrial standstill
    term:
      id: HP:0025478
      label: Atrial standstill
  description: >-
    Absence of atrial electrical and mechanical activity is the defining
    disease phenotype.
  evidence:
  - reference: PMID:35425822
    reference_title: "Left Bundle Branch Area Pacing in a Giant Atrium With Atrial Standstill: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Atrial standstill (AS) is a rare condition defined by the lack of atrial"
    explanation: >-
      Directly supports the defining atrial standstill phenotype.
- name: Absent P wave
  category: Cardiovascular
  diagnostic: true
  phenotype_term:
    preferred_term: Absent P wave
    term:
      id: HP:0033122
      label: Absent P wave
  electrophysiology:
    electrophysiology_modality: ECG
  reports_on:
  - target: Atrial Electrical Silence
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      The absent P wave is an ECG readout of absent atrial depolarization, not a
      separate causal step in disease progression.
    evidence:
    - reference: PMID:29387541
      reference_title: Atrial standstill in a pediatric patient with associated caveolin-3 mutation.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Atrial standstill (AS), a rare arrhythmogenic condition, is defined by (1) the absence of P waves in surface and intracavitary electrocardiograms (ECGs)"
      explanation: The diagnostic definition makes absent P waves an electrophysiologic readout of atrial silence.
  description: >-
    Surface ECG lacks atrial P waves because atrial depolarization is absent.
  evidence:
  - reference: PMID:16188595
    reference_title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "P waves on surface ECG, and his right atrium could not be captured by pacing."
    explanation: >-
      Supports absent P waves as a direct ECG manifestation of atrial
      standstill.
- name: Bradycardia
  category: Cardiovascular
  phenotype_term:
    preferred_term: Bradycardia
    term:
      id: HP:0001662
      label: Bradycardia
  description: >-
    Bradycardia occurs when atrial activation is absent and rhythm depends on
    junctional or ventricular escape activity.
  evidence:
  - reference: PMID:35425822
    reference_title: "Left Bundle Branch Area Pacing in a Giant Atrium With Atrial Standstill: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "symptomatic bradycardia, which requires permanent pacemaker (PPM) implantation."
    explanation: >-
      Supports symptomatic bradycardia as a typical manifestation.
- name: Syncope and presyncope
  category: Cardiovascular
  phenotype_term:
    preferred_term: Syncope
    term:
      id: HP:0001279
      label: Syncope
  description: >-
    Severe bradycardia or pauses may cause transient cerebral hypoperfusion,
    resulting in presyncope or syncope.
  evidence:
  - reference: PMID:29387541
    reference_title: Atrial standstill in a pediatric patient with associated caveolin-3 mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "An African American male patient presented with palpitations and syncope at the age of 12 years."
    explanation: >-
      Supports syncope as a reported clinical manifestation.
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "This included a pause of 8.4 seconds, which was associated with presyncope."
    explanation: >-
      Supports presyncope from long pauses in atrial standstill.
- name: Ventricular tachycardia
  category: Cardiovascular
  phenotype_term:
    preferred_term: Ventricular tachycardia
    term:
      id: HP:0004756
      label: Ventricular tachycardia
  description: >-
    Ventricular tachycardia is not part of the defining atrial electromechanical
    failure, but occurred in a clinically important subset of pediatric cases,
    particularly within severe SCN5A overlap phenotypes.
  evidence:
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Arrhythmias included 16 (80%) with atrial/supraventricular arrhythmias and 8 (40%) with ventricular tachycardia, including 4 with cardiac arrests."
    explanation: The multicenter pediatric cohort documents ventricular tachycardia as a non-defining but serious associated phenotype.
- name: Cardiac arrest
  category: Cardiovascular
  phenotype_term:
    preferred_term: Cardiac arrest
    term:
      id: HP:0001695
      label: Cardiac arrest
  description: >-
    Cardiac arrest is a high-risk complication concentrated in severe pediatric
    and biallelic SCN5A-associated presentations rather than a universal feature
    of atrial standstill.
  evidence:
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Ventricular arrhythmias and cardiac arrest were more commonly seen in patients with biallelic SCN5A variants."
    explanation: The cohort links cardiac arrest risk particularly to biallelic SCN5A disease.
- name: Right atrial enlargement
  category: Cardiovascular
  phenotype_term:
    preferred_term: Right atrial enlargement
    term:
      id: HP:0030718
      label: Right atrial enlargement
  description: >-
    Right atrial enlargement can occur as part of atrial structural remodeling in
    atrial standstill.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The right and left atria were markedly dilated on echocardiography"
    explanation: >-
      Supports right atrial enlargement in a reported atrial standstill case.
- name: Left atrial enlargement
  category: Cardiovascular
  phenotype_term:
    preferred_term: Left atrial enlargement
    term:
      id: HP:0031295
      label: Left atrial enlargement
  description: >-
    Left atrial enlargement can occur alongside right atrial dilation in
    advanced or partial atrial standstill.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The right and left atria were markedly dilated on echocardiography"
    explanation: >-
      Supports left atrial enlargement in a reported atrial standstill case.
- name: Thromboembolic stroke
  category: Neurological
  phenotype_term:
    preferred_term: Stroke
    term:
      id: HP:0001297
      label: Stroke
  description: >-
    Thromboembolic stroke is a serious complication of atrial mechanical
    standstill and blood stasis. Broader cardiomyopathy features can add risk but
    are not required.
  evidence:
  - reference: PMID:32755394
    reference_title: "Cardiac Emerinopathy: A Nonsyndromic Nuclear Envelopathy With Increased Risk of Thromboembolic Stroke Due to Progressive Atrial Standstill and Left Ventricular Noncompaction."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, a strong family history of stroke observed in these families was"
    explanation: >-
      Supports thromboembolic stroke risk from atrial standstill in EMD/LVNC
      families.
  - reference: PMID:39669928
    reference_title: Atrial standstill in a young patient with ischemic stroke associated with inheritance of a novel HCN4 mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We present a case of HCN4 gene mutation presenting with atrial standstill and"
    explanation: >-
      Supports stroke as a reported complication in a young patient with atrial
      standstill.
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "During a median follow-up of 6.9 years (IQR: 1.2-13.3 years), 7 (35%) had thromboembolic events."
    explanation: The pediatric cohort establishes thromboembolism as a primary-standstill complication, although not every event was a stroke.
genetic:
- name: SCN5A
  presence: Positive
  association: Established causative gene in familial atrial standstill
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: SCN5A
    term:
      id: hgnc:10593
      label: SCN5A
  notes: >-
    Monoallelic, homozygous, and compound-heterozygous SCN5A presentations have
    been reported. Penetrance can be incomplete in monoallelic families, while
    biallelic disease tends toward earlier and more severe overlap arrhythmia.
    The 65% figure below is specific to a 20-patient pediatric cohort that
    excluded acquired disease and is not a population-wide case fraction.
  case_fractions:
  - population: Retrospective multicenter pediatric primary-atrial-standstill cohort
    cohort_size: 20
    case_fraction_percent: 65.0
    notes: Thirteen of 20 patients had SCN5A variants; acquired disorders were excluded.
    evidence:
    - reference: PMID:36435694
      reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Genetic testing identified SCN5A variants in 13 patients (65%)."
      explanation: Directly quantifies the SCN5A share in this selected pediatric cohort.
  evidence:
  - reference: PMID:29781517
    reference_title: A homozygous SCN5A mutation associated with atrial standstill and sudden death.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "RESULTS: A novel homozygous SCN5A mutation, p.V1340L, was identified in the"
    explanation: >-
      Supports SCN5A as a familial atrial standstill gene.
  - reference: PMID:16188595
    reference_title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The novel SCN5A mutation L212P was identified in the proband"
    explanation: >-
      Supports an additional SCN5A variant associated with congenital atrial
      standstill.
  - reference: PMID:41280527
    reference_title: "Clinical presentation and outcomes of patients with biallelic SCN5A variants: A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Sinus node dysfunction was the most prevalent phenotype (35/54, 65%), often associated with atrial standstill (20/34, 59%)."
    explanation: A 2025 systematic review establishes atrial standstill as a frequent component of severe biallelic SCN5A disease.
- name: GJA5
  presence: Positive
  association: Modifier of SCN5A-associated atrial standstill
  relationship_type: MODIFIER
  variant_origin: GERMLINE
  gene_term:
    preferred_term: GJA5
    term:
      id: hgnc:4279
      label: GJA5
  notes: >-
    GJA5 is modeled as a modifier/family-specific digenic contributor because
    the cited studies describe connexin-40 regulatory polymorphisms as modifying
    SCN5A expression of disease rather than as a standalone monogenic cause.
  evidence:
  - reference: PMID:12522116
    reference_title: A cardiac sodium channel mutation cosegregates with a rare connexin40 genotype in familial atrial standstill.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In this study, familial AS was associated with the concurrence of a cardiac sodium channel mutation and rare polymorphisms in the atrial-specific Cx40 gene."
    explanation: The large-family study supports concurrence of SCN5A and GJA5 variation.
  - reference: PMID:16188595
    reference_title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "genetic factor that modifies the clinical manifestation of this inherited"
    explanation: >-
      Supports GJA5/connexin 40 as a modifier of inherited atrial standstill.
- name: MYL4
  presence: Positive
  association: Established causative gene for progressive heritable atrial cardiomyopathy with atrial standstill
  relationship_type: CAUSATIVE
  variant_origin: GERMLINE
  gene_term:
    preferred_term: MYL4
    term:
      id: hgnc:7585
      label: MYL4
  notes: >-
    The p.E11K variant cosegregated with a progressive atrial-selective
    cardiomyopathy and atrial standstill in a large family; engineered rat
    models provided functional corroboration. Other MYL4 variants can produce
    related atrial-fibrillation/cardiomyopathy phenotypes, so variant-level
    interpretation remains necessary.
  evidence:
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The mutation cosegregated with atrial standstill (selected as the principal presenting trait) with a logarithm of the odds score of 5.3."
    explanation: Strong human cosegregation supports MYL4 as a primary atrial-standstill gene.
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "The phenotype of rats with MYL4 mutation knock-in confirmed the causative role of the mutation."
    explanation: The knock-in model functionally corroborates the human genetic association.
inheritance:
- name: Autosomal dominant inheritance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  description: >-
    Dominant inheritance is established for the MYL4 p.E11K atrial
    cardiomyopathy family and is reported in some SCN5A families, often with
    incomplete penetrance or additional modifier effects.
  evidence:
  - reference: PMID:29080865
    reference_title: "Dysfunction of Myosin Light-Chain 4 (MYL4) Leads to Heritable Atrial Cardiomyopathy With Electrical, Contractile, and Structural Components: Evidence From Genetically-Engineered Rats."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The inheritance pattern was very likely to be autosomal dominant"
    explanation: The MYL4 family showed a dominant inheritance pattern.
- name: Autosomal recessive inheritance
  inheritance_term:
    preferred_term: Autosomal recessive inheritance
    term:
      id: HP:0000007
      label: Autosomal recessive inheritance
  description: >-
    Biallelic SCN5A variants can cause severe early-onset atrial standstill; the
    original homozygous family had unaffected heterozygous relatives, and later
    synthesis includes both homozygous and compound-heterozygous cases.
  evidence:
  - reference: PMID:29781517
    reference_title: A homozygous SCN5A mutation associated with atrial standstill and sudden death.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A novel homozygous SCN5A mutation, p.V1340L, was identified in the proband and her sister."
    explanation: The affected sisters carried homozygous SCN5A p.V1340L.
  - reference: PMID:41280527
    reference_title: "Clinical presentation and outcomes of patients with biallelic SCN5A variants: A systematic review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genotype analysis revealed 21 patients with homozygous SCN5A variants (34%) and 40 with compound heterozygous variants (66%)."
    explanation: The systematic review confirms both homozygous and compound-heterozygous SCN5A disease.
- name: Digenic inheritance
  inheritance_term:
    preferred_term: Digenic inheritance
    term:
      id: HP:0010984
      label: Digenic inheritance
  description: >-
    A family-specific digenic model combines an SCN5A variant with regulatory
    GJA5/connexin-40 polymorphisms. This is not asserted as the inheritance mode
    for all atrial standstill.
  evidence:
  - reference: PMID:16188595
    reference_title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Incomplete penetrance observed in atrial standstill has been attributed in part to the digenic inheritance of polymorphisms in the atrial-specific gap junction connexin 40 (Cx40) in conjunction with an SCN5A mutation."
    explanation: The study explicitly describes a digenic SCN5A/GJA5 inheritance model.
differential_diagnoses:
- name: Secondary or acquired atrial standstill
  description: >-
    Atrial electrical and mechanical silence can be induced by hypoxia,
    myocardial infarction, amyloidosis, muscular dystrophy, inflammatory atrial
    disease, and quinidine or digitalis toxicity. These cases share the final
    phenotype but do not establish the primary isolated disease modeled here.
  distinguishing_features:
  - A temporally related systemic, infiltrative, inflammatory, ischemic, metabolic, or drug exposure favors secondary standstill.
  - Reversibility after correction of the cause favors a transient secondary form.
  - Family history and pathogenic SCN5A or MYL4 variation favor primary inherited disease.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Previous reports showed that AS could be induced by various conditions, including hypoxia, muscular dystrophia, amyloidosis, myocardial infarction, and toxicity from quinidine or digitalis."
    explanation: The review portion of the case report identifies recognized secondary contexts.
- name: Broader inherited atrial or ventricular cardiomyopathy
  description: >-
    EMD/LMNA nuclear-envelope disease, NPPA atrial dilated cardiomyopathy, RYR2
    exon-3 deletion disease, and rare TAF1A or HCN4 reports can include atrial
    standstill as one manifestation. They should be represented under their
    broader gene-specific disease identities unless evidence establishes a
    primary isolated-standstill relationship.
  distinguishing_features:
  - Left ventricular noncompaction, ventricular dilation or fibrosis, skeletal myopathy, contractures, or a broad conduction/ventricular-arrhythmia phenotype favors a wider cardiomyopathy syndrome.
  - A gene-specific diagnosis outside SCN5A or MYL4 should not be promoted to primary isolated atrial standstill from a single case alone.
  evidence:
  - reference: PMID:32755394
    reference_title: "Cardiac Emerinopathy: A Nonsyndromic Nuclear Envelopathy With Increased Risk of Thromboembolic Stroke Due to Progressive Atrial Standstill and Left Ventricular Noncompaction."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac emerinopathy is a novel nonsyndromic X-linked progressive atrial standstill associated with LVNC and increased risk of thromboembolism."
    explanation: EMD-associated standstill is explicitly part of a distinct X-linked cardiac emerinopathy with LVNC.
- name: Familial sick sinus syndrome
  disease_term:
    preferred_term: familial sick sinus syndrome
    term:
      id: MONDO:0012061
      label: familial sick sinus syndrome
  description: >-
    Sinus-node dysfunction can cause pauses, bradycardia, and absent P waves
    without diffuse loss of atrial myocardium.
  distinguishing_features:
  - Preserved atrial electrograms, atrial capture, or mechanical A waves argue against complete atrial standstill.
  - Electroanatomic mapping can distinguish sinus-node failure from regional or diffuse atrial inexcitability.
- name: Atrial fibrillation
  disease_term:
    preferred_term: atrial fibrillation
    term:
      id: MONDO:0004981
      label: atrial fibrillation
  description: >-
    Fine atrial fibrillation can obscure discrete P waves and abolish effective
    atrial contraction, but atrial electrical activity remains disorganized
    rather than absent.
  distinguishing_features:
  - Fibrillatory surface or intracardiac activity favors atrial fibrillation.
  - Complete absence of atrial electrograms and failure of high-output atrial capture favor atrial standstill.
diagnosis:
- name: Electrocardiography for absent P waves and escape rhythm
  description: >-
    Surface ECG is the first-line diagnostic test, showing absent P waves and a
    junctional or ventricular escape rhythm rather than organized atrial
    activation. Absent P waves alone are not specific and must be paired with
    evidence of absent atrial mechanical activity and, when needed, atrial
    inexcitability.
  diagnosis_term:
    preferred_term: electrocardiography
    term:
      id: NCIT:C38053
      label: Electrocardiography
  results: Absent P waves with bradycardic escape rhythm support atrial standstill.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The absence of P waves and bradycardia, along with a wide QRS complex, are seen on the electrocardiogram (ECG)."
    explanation: >-
      Supports ECG recognition of absent P waves and bradycardia.
- name: Echocardiography for absent atrial contraction
  description: >-
    Doppler echocardiography assesses mechanical atrial activity and can show
    loss of A waves or atrial enlargement.
  diagnosis_term:
    preferred_term: echocardiography
    term:
      id: NCIT:C16525
      label: Echocardiography Test
  results: Absent transmitral or transtricuspid A waves support loss of atrial mechanical contraction.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "No mechanical atrial activity was observed in a Doppler study of the mitral and tricuspid inflow regions"
    explanation: >-
      Supports Doppler echocardiography as a diagnostic method for atrial
      mechanical standstill.
- name: Electrophysiology study and mapping
  description: >-
    Electrophysiology study confirms atrial inexcitability and identifies any
    residual viable atrial myocardium for potential atrial lead placement.
  diagnosis_term:
    preferred_term: clinical cardiac electrophysiologist evaluation
    term:
      id: NCIT:C80414
      label: Cardiac Electrophysiology Study
  results: Failure to capture the atria and low-voltage or scarred regions confirm atrial electrical standstill.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In atrial standstill when pacemaker implantations are thought to be necessary, evaluation by electrophysiological study should be considered before implantation."
    explanation: >-
      Supports EP study before pacing when atrial standstill is suspected.
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Only inside the CS did atrial electrical activities remain."
    explanation: >-
      Supports mapping residual viable atrial tissue, including coronary sinus
      activity, before device planning.
- name: Cardiac magnetic resonance imaging for fibrosis and cardiomyopathy assessment
  description: >-
    Cardiac MRI can assess atrial and ventricular morphology, function, and
    delayed enhancement when a broader structural, inflammatory, infiltrative,
    or genetic cardiomyopathy is a concern. A normal MRI does not exclude the
    electrical diagnosis.
  diagnosis_term:
    preferred_term: magnetic resonance imaging procedure
    term:
      id: NCIT:C16809
      label: Magnetic Resonance Imaging
  results: Cardiac MRI may identify or help exclude associated cardiomyopathy; normal ventricular morphology and absent delayed enhancement do not exclude atrial standstill.
  evidence:
  - reference: PMID:29387541
    reference_title: Atrial standstill in a pediatric patient with associated caveolin-3 mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Cardiac magnetic resonance imaging showed normal morphology, function, and no delayed myocardial enhancement."
    explanation: >-
      Supports cardiac MRI as part of the diagnostic workup to evaluate cardiac
      structure, function, and delayed enhancement.
- name: Genetic testing for inherited atrial standstill
  description: >-
    Genetic testing is indicated when familial, early-onset, progressive, or
    syndromic atrial standstill suggests inherited channelopathy or
    cardiomyopathy.
  diagnosis_term:
    preferred_term: genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  results: Pathogenic SCN5A or MYL4 variants can support a primary inherited diagnosis; GJA5 findings require modifier-level interpretation, and broader panels can identify distinct cardiomyopathy syndromes.
  evidence:
  - reference: PMID:16188595
    reference_title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "underwent genetic screening of SCN5A and atrial-specific genes including Cx40."
    explanation: >-
      Supports genetic testing of SCN5A and atrial conduction genes in familial
      or apparently sporadic atrial standstill.
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Genetic testing identified SCN5A variants in 13 patients (65%)."
    explanation: The multicenter cohort supports a high diagnostic yield for SCN5A testing in selected pediatric primary cases.
treatments:
- name: Permanent pacemaker implantation
  therapeutic_modality: DEVICE
  description: >-
    Persistent or symptomatic atrial standstill often requires permanent pacing,
    commonly ventricular pacing when atrial capture is absent. Physiologic
    ventricular pacing such as left bundle branch area pacing has been reported
    to reduce pacing dyssynchrony risk in selected cases.
  treatment_term:
    preferred_term: pacemaker implantation
    term:
      id: NCIT:C80434
      label: Pacemaker Placement
  target_phenotypes:
  - preferred_term: Bradycardia
    term:
      id: HP:0001662
      label: Bradycardia
  target_mechanisms:
  - target: Escape Rhythm Bradycardia
    treatment_effect: MODULATES
    description: >-
      Permanent pacing stabilizes ventricular rate when escape rhythm
      bradycardia causes symptoms or pacing dependence.
  evidence:
  - reference: PMID:35425822
    reference_title: "Left Bundle Branch Area Pacing in a Giant Atrium With Atrial Standstill: A Case Report and Literature Review."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "symptomatic bradycardia, which requires permanent pacemaker (PPM) implantation."
    explanation: >-
      Supports pacemaker implantation for symptomatic bradycardia in atrial
      standstill.
  - reference: PMID:29387541
    reference_title: Atrial standstill in a pediatric patient with associated caveolin-3 mutation.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "lack of right atrial sensing or capture with transvenous atrial lead placement attempts, so a single-chamber ventricular pacemaker was placed."
    explanation: >-
      Supports ventricular pacemaker placement when atrial sensing/capture fails.
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pacemakers were implanted in 18 (90%). Although atrial leads were attempted in 15, only 4 achieved pacing at implantation."
    explanation: The multicenter pediatric cohort documents frequent device need and the difficulty of atrial capture.
- name: Coronary sinus atrial lead placement for partial atrial standstill
  therapeutic_modality: DEVICE
  description: >-
    In partial atrial standstill, EP mapping may identify residual excitable
    tissue in the coronary sinus, allowing atrial lead placement and
    atrioventricular synchronous pacing.
  treatment_term:
    preferred_term: pacemaker implantation
    term:
      id: NCIT:C80434
      label: Pacemaker Placement
  target_mechanisms:
  - target: Atrial Electrical Silence
    treatment_effect: MODULATES
    description: >-
      Coronary sinus lead placement can use residual atrial electrical activity
      when diffuse right atrial capture is not possible.
  evidence:
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Pacemaker implantation was necessary owing to symptomatic sick sinus syndrome."
    explanation: >-
      Supports pacemaker implantation as required in the reported partial
      atrial standstill case.
  - reference: PMID:31285994
    reference_title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We succeeded in placing the atrial lead with the initial attempt, and we placed the lead of the pacemaker proximally inside the CS"
    explanation: >-
      Supports coronary sinus atrial lead placement when residual activity is
      mapped there.
- name: Anticoagulant therapy for thromboembolic risk
  therapeutic_modality: SMALL_MOLECULE
  description: >-
    Anticoagulation is used to reduce thromboembolism from atrial mechanical
    standstill. The strongest disease-specific evidence is a retrospective
    pediatric cohort in which events clustered among patients without effective
    atrial pacing; there is no randomized atrial-standstill trial defining agent,
    threshold, or duration.
  treatment_term:
    preferred_term: anticoagulant agent therapy
    term:
      id: NCIT:C63341
      label: Anticoagulation Therapy
  target_phenotypes:
  - preferred_term: Stroke
    term:
      id: HP:0001297
      label: Stroke
  target_mechanisms:
  - target: Thromboembolic Risk from Atrial Stasis
    treatment_effect: INHIBITS
    description: >-
      Anticoagulant therapy is intended to reduce thromboembolic risk arising
      from atrial paralysis and associated cardiomyopathy.
  evidence:
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Patients without the capacity for atrial pacing are at risk for thromboembolic events and warrant anticoagulation."
    explanation: >-
      The multicenter cohort directly recommends anticoagulation for patients
      without effective atrial pacing; this remains observational evidence.
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Of these, none had atrial pacing, 6 were not on anticoagulation, and 1 was on aspirin."
    explanation: >-
      Event clustering supports the rationale but does not estimate comparative
      anticoagulant efficacy or establish a treatment threshold.
discussions:
- discussion_id: disc_atrial_standstill_management_evidence
  prompt: >-
    Which pacing configuration and anticoagulation strategy best prevent
    thromboembolism, pacing-related ventricular dysfunction, and sudden events
    across partial, diffuse, monoallelic, and biallelic atrial standstill?
  kind: KNOWLEDGE_GAP
  status: OPEN
  attaches_to:
  - treatments#Permanent pacemaker implantation
  - treatments#Coronary sinus atrial lead placement for partial atrial standstill
  - treatments#Anticoagulant therapy for thromboembolic risk
  - pathophysiology#Thromboembolic Risk from Atrial Stasis
  rationale: >-
    Management evidence is a retrospective 20-patient pediatric cohort plus
    case reports. As of a ClinicalTrials.gov review on 2026-07-20, no study
    explicitly enrolled atrial standstill as a condition; the sole API match
    for the exact condition, NCT06166277, enrolled vasovagal syncope, Mobitz I AV
    block, and sinus pause and acquired the atrial-standstill label only through
    derived MeSH indexing. No disease-specific interventional trial was added.
  proposed_experiments:
  - experiment_id: exp_atrial_standstill_multinational_registry
    name: Prospective multinational atrial standstill registry
    description: >-
      Enroll primary and secondary cases with explicit etiologic classification,
      genotype, partial-versus-diffuse mapping, atrial capture status, pacing
      strategy, anticoagulant exposure, bleeding, thromboembolism, ventricular
      function, arrhythmias, and mortality using prespecified longitudinal
      endpoints.
  evidence:
  - reference: PMID:36435694
    reference_title: "Atrial Standstill in the Pediatric Population: A Multi-Institution Collaboration."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Studies to date have been limited."
    explanation: The multicenter investigators explicitly identify the limited evidence base.
  posed_date: "2026-07-20T00:00:00Z"
- discussion_id: disc_myl4_model_translation
  prompt: >-
    Does MYL4-dependent autophagic-flux failure operate in human atrial tissue,
    and can restoring MYL4 safely reverse established atrial fibrosis or
    electrical silence?
  kind: HUMAN_MODEL_MISMATCH
  status: OPEN
  attaches_to:
  - pathophysiology#MYL4 Loss of Function
  - pathophysiology#Atrial Cardiomyocyte Autophagic and Survival Dysfunction
  - pathophysiology#Atrial Fibrosis and Low-Voltage Scar
  rationale: >-
    Knock-in rats and cultured cardiomyocytes support lysosomal/autophagic
    dysfunction and adenoviral MYL4 rescue, but no human atrial-tissue
    confirmation or clinical intervention establishes relevance, reversibility,
    dose, or safety in patients.
  proposed_experiments:
  - experiment_id: exp_myl4_human_atrial_validation
    name: Human MYL4 atrial tissue and engineered-tissue validation
    description: >-
      Compare atrial tissue or patient-derived atrial engineered tissues from
      pathogenic-MYL4 carriers and matched controls for autophagic flux,
      lysosomal function, myocyte survival, conduction, contraction, and fibrosis;
      test controlled MYL4 restoration with rescue and off-target criteria.
  evidence:
  - reference: PMID:36645977
    reference_title: Myosin light-chain 4 gene-transfer attenuates atrial fibrosis while correcting autophagic flux dysregulation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "MYL4 protein overexpression attenuated atrial structural remodeling and autophagy dysfunction."
    explanation: Rat gene-transfer rescue motivates translation while remaining preclinical.
  posed_date: "2026-07-20T00:00:00Z"
references:
- reference: DOI:10.3389/fcvm.2022.836964
  title: "Left Bundle Branch Area Pacing in a Giant Atrium With Atrial Standstill: A Case Report and Literature Review"
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1111/anec.12399
  title: "Persistent atrial standstill following the Cox-maze III procedure: reversal with sustained atrial pacing"
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1002/joa3.13150
  title: Atrial standstill in a young patient with ischemic stroke associated with inheritance of a novel HCN4 mutation
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.20452/pamw.4451
  title: Clinical classification of rare cardiac arrhythmogenic and conduction disorders, and rare arrhythmias
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.17264/stmarieng.15.21
  title: "Atrial Standstill: A Rare Cause of Pediatric Stroke and Management Strategies"
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1016/j.hrcr.2019.03.008
  title: A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1016/j.hrthm.2005.06.032
  title: Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1111/pace.13386
  title: A homozygous SCN5A mutation associated with atrial standstill and sudden death
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1161/circep.120.008712
  title: Cardiac Emerinopathy
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1016/j.hrcr.2017.07.014
  title: Atrial standstill in a pediatric patient with associated caveolin-3 mutation
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.1016/j.jccase.2016.06.010
  title: Atrial standstill in suspected isolated cardiac sarcoidosis
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
- reference: DOI:10.3390/biology11040530
  title: "Clinical Profile, Arrhythmias, and Adverse Cardiac Outcomes in Emery-Dreifuss Muscular Dystrophies: A Systematic Review of the Literature"
  found_in:
  - Atrial_Standstill-deep-research-falcon.md
review_notes: >-
  Evidence and disease-boundary review completed 2026-07-20. SCN5A and MYL4 are
  retained as primary causative genes; GJA5 is retained only as a modifier and
  family-specific digenic contributor. EMD, LMNA, NPPA, RYR2, TAF1A, and HCN4
  reports are not promoted to primary isolated-atrial-standstill genes because
  they describe broader cardiomyopathy/conduction syndromes or remain
  case-level associations. The published CAV3 p.Leu84Pro case is especially
  uncertain: the source states that the variant was reclassified as a variant
  of unknown significance because functional and segregation data were absent.
  The current-trial audit found no atrial-standstill-specific interventional
  study; NCT06166277 was rejected as an automated MeSH false-positive rather
  than represented under clinical_trials. Management therefore remains based
  on observational cohorts, electrophysiologic mapping, and case reports.
notes: >-
  The defining boundary requires both atrial electrical silence and loss of
  mechanical atrial activity. Absent P waves or sinus-node dysfunction alone do
  not establish atrial standstill. Partial standstill can retain localized
  excitable tissue, so electrophysiologic mapping can alter device strategy.
📚

References & Deep Research

References

12
DOI:10.3389/fcvm.2022.836964
Left Bundle Branch Area Pacing in a Giant Atrium With Atrial Standstill: A Case Report and Literature Review
No top-level findings curated for this source.
DOI:10.1111/anec.12399
Persistent atrial standstill following the Cox-maze III procedure: reversal with sustained atrial pacing
No top-level findings curated for this source.
DOI:10.1002/joa3.13150
Atrial standstill in a young patient with ischemic stroke associated with inheritance of a novel HCN4 mutation
No top-level findings curated for this source.
DOI:10.20452/pamw.4451
Clinical classification of rare cardiac arrhythmogenic and conduction disorders, and rare arrhythmias
No top-level findings curated for this source.
DOI:10.17264/stmarieng.15.21
Atrial Standstill: A Rare Cause of Pediatric Stroke and Management Strategies
No top-level findings curated for this source.
DOI:10.1016/j.hrcr.2019.03.008
A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus
No top-level findings curated for this source.
DOI:10.1016/j.hrthm.2005.06.032
Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms
No top-level findings curated for this source.
DOI:10.1111/pace.13386
A homozygous SCN5A mutation associated with atrial standstill and sudden death
No top-level findings curated for this source.
DOI:10.1161/circep.120.008712
Cardiac Emerinopathy
No top-level findings curated for this source.
DOI:10.1016/j.hrcr.2017.07.014
Atrial standstill in a pediatric patient with associated caveolin-3 mutation
No top-level findings curated for this source.
DOI:10.1016/j.jccase.2016.06.010
Atrial standstill in suspected isolated cardiac sarcoidosis
No top-level findings curated for this source.
DOI:10.3390/biology11040530
Clinical Profile, Arrhythmias, and Adverse Cardiac Outcomes in Emery-Dreifuss Muscular Dystrophies: A Systematic Review of the Literature
No top-level findings curated for this source.

Deep Research

1
Falcon ▸
Atrial Standstill — Comprehensive Disease Characteristics Research Report
Edison Scientific Literature 41 citations 2026-05-06T13:54:43.180669

Atrial Standstill — Comprehensive Disease Characteristics Research Report

Target disease: Atrial standstill (AS)
Category: Heart disorder (arrhythmia / atrial cardiomyopathy)
Report scope: Evidence is primarily from peer‑reviewed human case reports/families and focused cohorts/reviews. No EHR-derived aggregate datasets were retrieved in this run.

Executive summary

Atrial standstill is a rare atrial arrhythmia/atrial myopathy defined by the absence of atrial electrical activity and loss of atrial mechanical contraction, producing absent P waves, atrial electrical silence on intracardiac recordings, and typically junctional/escape bradycardia. It can be transient vs persistent/permanent and partial vs diffuse, and may progress over time from focal right atrial involvement to biatrial electrical failure. AS may arise from acquired/reversible causes (e.g., hyperkalemia, drug toxicity, myocarditis/MI) or genetic/syndromic atrial cardiomyopathies, notably involving SCN5A and EMD among others. Clinically important complications include thromboembolism/stroke from atrial stasis and need for permanent pacing; contemporary real‑world reports demonstrate physiologic pacing approaches such as left bundle branch area pacing (LBBAP) in patients with AS and giant atria. (zheng2022leftbundlebranch pages 1-2, anand2024atrialstandstillin pages 1-3, agrawal2017persistentatrialstandstill pages 3-4, ishikawa2020cardiacemerinopathy pages 1-4)

1. Disease information

1.1 Overview and definition (current understanding)

Multiple sources converge on a core definition: atrial standstill is characterized by absence of atrial electrical activity and atrial mechanical activity. For example, a recent pacing case report states: “Atrial standstill (AS) is a rare condition defined by the lack of atrial electrical and mechanical activities.” (Frontiers in Cardiovascular Medicine; published 2022-03, https://doi.org/10.3389/fcvm.2022.836964) (zheng2022leftbundlebranch pages 1-2). A noninvasive electrophysiology case report similarly defines it as total absence of atrial electrical activity in one or both atria and describes diagnostic confirmation via absent atrial mechanical contraction (Doppler “A” waves, etc.) (published 2017-03, https://doi.org/10.1111/anec.12399) (agrawal2017persistentatrialstandstill pages 1-3, agrawal2017persistentatrialstandstill pages 3-4).

1.2 Key diagnostic concept

A practical set of diagnostic criteria is summarized in a 2024 case report: atrial standstill is characterized by (1) absence of P waves, (2) narrow QRS, (3) evidence of atrial paralysis (e.g., absent jugular venous “a” waves and absent Doppler A wave / tissue Doppler a′), and (4) inability to stimulate/capture the atria even with pacing (Journal of Arrhythmia; published 2024-09, https://doi.org/10.1002/joa3.13150) (anand2024atrialstandstillin pages 1-3).

1.3 Synonyms / terminology

AS is described as transient vs persistent (“permanent”) and partial vs total/diffuse. A clinical review‑style case report explicitly notes classification “as transient (temporary) or persistent (also referred to as permanent)” and uses “partial atrial standstill” for one‑atrium or localized preservation of atrial activity (agrawal2017persistentatrialstandstill pages 1-3). A HeartRhythm Case Reports article also uses “permanent atrial standstill,” “partial atrial electrical standstill,” and “persistent atrial paralysis.” (suzuki2019acaseof pages 3-5)

1.4 Disease identifiers (ontology/coding)

The retrieved evidence contains an explicit Orphanet number and an OMIM reference, but MONDO and MeSH identifiers were not retrieved.

Identifier system (Orphanet/ICD-10/OMIM/MeSH/MONDO/Other) Code/ID Label Notes on evidence strength Source (paper title, year) URL
Orphanet ORPHA:1344 Atrial standstill Reported in a classification table as an Orphanet identifier for atrial standstill; strongest explicit disease identifier found in retrieved evidence (podolec2019clinicalclassificationof pages 2-3) Clinical classification of rare cardiac arrhythmogenic and conduction disorders, and rare arrhythmias (2019) https://doi.org/10.20452/pamw.4451
ICD-10 I45.5 Other specified heart block Listed for atrial standstill as a sample code in the classification table; article notes some rare cardiac disorders are not referenced in ICD-10, so mapping should be treated cautiously (podolec2019clinicalclassificationof pages 2-3) Clinical classification of rare cardiac arrhythmogenic and conduction disorders, and rare arrhythmias (2019) https://doi.org/10.20452/pamw.4451
OMIM 108770 Atrial standstill OMIM number appears in a review of 1q21.1 CNVs that mentions “atrial standstill (OMIM 108770)”; indirect evidence rather than a primary disease ontology source in this conversation (podolec2019clinicalclassificationof pages 2-3) Prenatal phenotypes and pregnancy outcomes of fetuses with recurrent 1q21.1 microdeletions and microduplications (2023) https://doi.org/10.3389/fmed.2023.1207891
MeSH Not found in retrieved evidence No explicit MeSH heading or ID for atrial standstill was retrieved in the available evidence (podolec2019clinicalclassificationof pages 2-3) Not found in retrieved evidence
MONDO Not found in retrieved evidence No explicit MONDO identifier for atrial standstill was retrieved in the available evidence (podolec2019clinicalclassificationof pages 2-3) Not found in retrieved evidence
Other VI-1C-2 Atrial standstill Internal/clinical rare cardiac disease classification code (RCDD code), not a standard biomedical ontology identifier (podolec2019clinicalclassificationof pages 2-3) Clinical classification of rare cardiac arrhythmogenic and conduction disorders, and rare arrhythmias (2019) https://doi.org/10.20452/pamw.4451
Other (synonym/terminology) Atrial standstill (AS) Standard abbreviation used across case reports/reviews; disease-level terminology rather than ontology identifier (zheng2022leftbundlebranch pages 1-2, kato2024atrialstandstilla pages 1-3) Left Bundle Branch Area Pacing in a Giant Atrium With Atrial Standstill (2022); Atrial Standstill: A Rare Cause of Pediatric Stroke and Management Strategies (2024) https://doi.org/10.3389/fcvm.2022.836964; https://doi.org/10.17264/stmarieng.15.21
Other (synonym/terminology) Persistent atrial standstill Explicitly described as a persistent/permanent form in the literature; synonym reflects temporal subtype rather than distinct ontology code (agrawal2017persistentatrialstandstill pages 1-3, agrawal2017persistentatrialstandstill pages 3-4) Persistent atrial standstill following the Cox-maze III procedure (2017) https://doi.org/10.1111/anec.12399
Other (synonym/terminology) Permanent atrial standstill Used interchangeably with persistent atrial standstill in retrieved evidence; terminology/synonym only (agrawal2017persistentatrialstandstill pages 1-3, suzuki2019acaseof pages 3-5) Persistent atrial standstill following the Cox-maze III procedure (2017); A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus (2019) https://doi.org/10.1111/anec.12399; https://doi.org/10.1016/j.hrcr.2019.03.008
Other (synonym/terminology) Partial atrial standstill Common term for regional/unilateral atrial involvement; descriptive subtype rather than separate coded disease (agrawal2017persistentatrialstandstill pages 1-3, makita2005congenitalatrialstandstill pages 1-2, suzuki2019acaseof pages 3-5) Persistent atrial standstill following the Cox-maze III procedure (2017); Congenital atrial standstill associated with coinheritance of a novel SCN5A mutation and connexin 40 polymorphisms (2005); A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus (2019) https://doi.org/10.1111/anec.12399; https://doi.org/10.1016/j.hrthm.2005.06.032; https://doi.org/10.1016/j.hrcr.2019.03.008
Other (synonym/terminology) Persistent atrial paralysis Alternate wording used in retrieved case literature; terminology/synonym only (suzuki2019acaseof pages 3-5) A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus (2019) https://doi.org/10.1016/j.hrcr.2019.03.008

Table: This table compiles disease identifiers and commonly used terminology for atrial standstill using only the retrieved evidence from the conversation. It distinguishes explicit ontology/code evidence from descriptive synonyms and flags weaker mappings such as sample ICD-10 codes.

Note on coding: The ICD‑10 mapping for atrial standstill is not standardized in the retrieved evidence; one classification paper lists an ICD‑10 entry as a sample code and notes some rare cardiac disorders are not referenced in ICD‑10 (podolec2019clinicalclassificationof pages 2-3).

2. Etiology

2.1 Disease causal factors

2.1.1 Genetic causes (primary atrial cardiomyopathy/channelopathy)

Evidence supports a heterogeneous genetic architecture, with strong data for SCN5A and for EMD (emerin) in a defined X‑linked syndrome.

  • SCN5A (Nav1.5): Familial congenital/progressive atrial standstill has been linked to loss‑of‑function SCN5A variants, sometimes with modifier effects from atrial gap junction variants.
  • Makita et al. (Heart Rhythm; 2005-10, https://doi.org/10.1016/j.hrthm.2005.06.032) report a family with a novel SCN5A p.Leu212Pro and propose modifying effects of connexin‑40 (GJA5) polymorphisms (makita2005congenitalatrialstandstill pages 1-2).
  • Tan et al. (PACE; 2018-06, https://doi.org/10.1111/pace.13386) report a homozygous SCN5A p.Val1340Leu variant with atrial standstill and sudden death risk, supported by patch‑clamp loss‑of‑function (tan2018ahomozygousscn5a pages 1-4).
  • EMD (emerin): Ishikawa et al. describe “cardiac emerinopathy,” a nonsyndromic X‑linked condition characterized by progressive atrial arrhythmias culminating in atrial standstill and associated with LV noncompaction (LVNC) and thromboembolism (Circulation: Arrhythmia and Electrophysiology; 2020-10, https://doi.org/10.1161/circep.120.008712) (ishikawa2020cardiacemerinopathy pages 1-4).
  • HCN4: A 2024 report links a novel HCN4 missense change with atrial standstill and ischemic stroke in a young patient (Journal of Arrhythmia; 2024-09, https://doi.org/10.1002/joa3.13150) (anand2024atrialstandstillin pages 1-3).
  • CAV3: A pediatric case report describes atrial standstill with a CAV3 p.Leu84Pro variant that was later reclassified as a VUS, emphasizing uncertainty for causality in this gene (HeartRhythm Case Reports; 2017-11, https://doi.org/10.1016/j.hrcr.2017.07.014) (gal2017atrialstandstillin pages 1-2).

A structured gene/variant summary from the retrieved evidence is provided here:

Gene (HGNC symbol) Inheritance/zygosity (if described) Variant (HGVS protein/cDNA or descriptor) Evidence type (family/case report/cohort) Key phenotypes/complications (stroke, LVNC, conduction disease) Functional evidence (e.g., loss-of-function patch clamp) Publication (year, journal) URL
SCN5A Familial; heterozygous in proband and father with incomplete penetrance; atrial phenotype modified by GJA5 polymorphisms p.Leu212Pro (L212P); coinherited GJA5/Cx40 polymorphisms as modifiers Familial case report with electrophysiology and channel studies Congenital/progressive atrial dysfunction to atrial standstill; absent P waves; right atrium not capturable by pacing; bradyarrhythmia/conduction disease; variable penetrance in family Marked loss-of-function of Nav1.5 with hyperpolarizing shifts of activation/inactivation and delayed recovery; authors infer Cx40 polymorphisms may reduce atrial conduction reserve and modify phenotype (makita2005congenitalatrialstandstill pages 1-2) Makita et al., 2005, Heart Rhythm https://doi.org/10.1016/j.hrthm.2005.06.032
SCN5A Familial; homozygous affected sisters, heterozygous relatives asymptomatic p.Val1340Leu (V1340L) Familial case report with segregation and patch clamp Complete atrial standstill in proband, partial atrial standstill in sister; absent electrical/mechanical atrial activity; sudden death risk reported in family Loss-of-function Nav1.5; reduced current density and depolarizing shift in steady-state activation (WT −35.3±1.62 mV vs V1340L −22.4±2.59 mV; P=0.001) (tan2018ahomozygousscn5a pages 1-4) Tan et al., 2018, Pacing and Clinical Electrophysiology https://doi.org/10.1111/pace.13386
EMD X-linked recessive; affected male carriers, female carriers often asymptomatic Start-loss, splicing, and missense EMD mutations (specific variants not detailed in retrieved evidence) Targeted sequencing cohort plus family-based clinical characterization Progressive atrial arrhythmias culminating in atrial standstill; LVNC; familial stroke/thromboembolism risk; conduction disease; need for pacemaker/defibrillator implantation Genetic/segregation evidence; no patch-clamp assay reported in retrieved excerpt; mechanistic interpretation supports a nonsyndromic “cardiac emerinopathy” causing progressive atrial myopathy (ishikawa2020cardiacemerinopathy pages 1-4) Ishikawa et al., 2020, Circulation: Arrhythmia and Electrophysiology https://doi.org/10.1161/circep.120.008712
HCN4 Autosomal dominant familial inheritance described; heterozygous in reported patient/family c.2063A>C, p.Asn688Thr Case report with family history and multimodal cardiac evaluation Atrial standstill in a young patient with ischemic stroke; absent atrial contraction; dilated right atrium; biatrial late gadolinium enhancement; familial sick sinus syndrome/conduction phenotype No direct in vitro functional assay reported in retrieved excerpt; evidence includes segregation with familial sick sinus syndrome plus EP/MRI phenotype consistent with atrial paralysis (anand2024atrialstandstillin pages 1-3) Anand et al., 2024, Journal of Arrhythmia https://doi.org/10.1002/joa3.13150
CAV3 Not clearly established in retrieved evidence; pediatric single-case finding p.Leu84Pro (L84P); initially likely pathogenic, later reclassified as VUS Pediatric case report Atrial standstill with right atrial scar/electrical silence; inducible left atrial tachycardia; progressive inability to sense/capture atrium; ventricular pacing dependence; no stroke/LVNC reported in retrieved excerpt No direct functional assay in retrieved excerpt; rarity noted (not observed in 6500 individuals in NHLBI GO Exome Sequencing Project), but causal role remains uncertain because variant was reclassified as VUS (gal2017atrialstandstillin pages 1-2) Gal et al., 2017, HeartRhythm Case Reports https://doi.org/10.1016/j.hrcr.2017.07.014

Table: This table summarizes key gene-level associations reported for atrial standstill in the retrieved evidence, including inheritance, variants, major clinical features, and available functional support. It is useful for distinguishing well-supported causal genes such as SCN5A and EMD from more tentative associations such as CAV3.

2.1.2 Acquired / potentially reversible causes

Case-based literature highlights multiple acquired triggers. Examples include hyperkalemia, drug toxicity (digoxin/digitalis, quinidine, verapamil, etc.), reflex syncope, and acute myocardial infarction, and inflammatory/infiltrative disease such as amyloidosis, muscular dystrophies, systemic lupus, and cardiac sarcoidosis (agrawal2017persistentatrialstandstill pages 3-4, suzuki2019acaseof pages 3-5, kim2016atrialstandstillin pages 1-2).

A notable mechanistic acquired example is suspected isolated cardiac sarcoidosis, where imaging (atrial LGE) and biopsy supported atrial fibrosis with inflammatory involvement associated with atrial electrical silence (Journal of Cardiology Cases; 2016-11, https://doi.org/10.1016/j.jccase.2016.06.010) (kim2016atrialstandstillin pages 1-2).

2.2 Risk factors

Risk factors in retrieved evidence are largely etiologic categories rather than quantified epidemiologic risks: - Underlying genetic cardiomyopathy/channelopathy (SCN5A; EMD; HCN4) (tan2018ahomozygousscn5a pages 1-4, ishikawa2020cardiacemerinopathy pages 1-4, anand2024atrialstandstillin pages 1-3) - Systemic/infiltrative/inflammatory disorders (e.g., sarcoidosis, amyloidosis) (kim2016atrialstandstillin pages 1-2, agrawal2017persistentatrialstandstill pages 3-4) - Metabolic or drug-related triggers (hyperkalemia; digoxin/digitalis; quinidine) (agrawal2017persistentatrialstandstill pages 3-4, suzuki2019acaseof pages 3-5)

2.3 Protective factors and gene–environment interactions

No protective genetic variants or robust gene–environment interaction analyses specific to atrial standstill were retrieved. Evidence is insufficient in this run.

3. Phenotypes

3.1 Core phenotype spectrum

Atrial standstill presents with a combination of electrical silence, mechanical failure, and downstream hemodynamic/thromboembolic consequences: - ECG: absent P waves; junctional or ventricular escape rhythm/bradycardia (zheng2022leftbundlebranch pages 1-2, makita2005congenitalatrialstandstill pages 1-2, anand2024atrialstandstillin pages 1-3). - Echo Doppler: absent transmitral/tricuspid A wave; absence of atrial contraction (agrawal2017persistentatrialstandstill pages 3-4, kato2024atrialstandstilla pages 1-3, zheng2022leftbundlebranch pages 1-2). - EP study: inability to capture atria with pacing; atrial electrogram inactivity or markedly low voltage; residual activity may persist in limited regions (e.g., coronary sinus) (suzuki2019acaseof pages 1-3, suzuki2019acaseof pages 3-5). - Structural atrial disease: atrial dilation/giant atrium, atrial fibrosis/scar (often inferred via low-voltage mapping or LGE on CMR) (zheng2022leftbundlebranch pages 1-2, anand2024atrialstandstillin pages 1-3, kim2016atrialstandstillin pages 1-2). - Complications: thromboembolism/stroke risk due to blood stasis from absent contraction (kato2024atrialstandstilla pages 1-3, anand2024atrialstandstillin pages 1-3, ishikawa2020cardiacemerinopathy pages 1-4).

3.2 Phenotype-to-HPO mapping

Phenotype/feature Suggested HPO term (name and HP ID) Notes
Absent P waves on surface ECG Atrial standstill (HP:0011703) Core electrical diagnostic feature of atrial standstill; reports describe no visible P waves on ECG, often with absent atrial electrograms as supportive EP evidence (agrawal2017persistentatrialstandstill pages 1-3, anand2024atrialstandstillin pages 1-3, zheng2022leftbundlebranch pages 1-2).
Junctional escape bradycardia / narrow-complex escape rhythm Bradycardia (HP:0001662); Junctional rhythm (HP:0011675) Typical rhythm disturbance when atrial activation is absent; often described as junctional or escape rhythm accompanying absent P waves (makita2005congenitalatrialstandstill pages 1-2, anand2024atrialstandstillin pages 1-3, zheng2022leftbundlebranch pages 1-2).
Atrial paralysis / no A wave on Doppler echocardiography Atrial standstill (HP:0011703) Mechanical criterion: absent atrial contraction shown by loss of A waves on mitral/tricuspid inflow Doppler, tissue Doppler a′, or jugular/pressure tracings (agrawal2017persistentatrialstandstill pages 3-4, anand2024atrialstandstillin pages 1-3, kato2024atrialstandstilla pages 1-3).
Inability to capture atrium on pacing / atrial inexcitability Atrial standstill (HP:0011703) EP criterion: failure to electrically stimulate/capture right atrium or coronary sinus even at high output; useful for confirming diagnosis and guiding lead strategy (suzuki2019acaseof pages 1-3, anand2024atrialstandstillin pages 1-3, kato2024atrialstandstilla pages 1-3).
Atrial dilation / giant atrium Left atrial dilatation (HP:0001698); Right atrial dilatation (HP:0001719) Structural atrial disease is common in reported cases, including giant atrium and marked right atrial dilation on echo/MRI (zheng2022leftbundlebranch pages 1-2, anand2024atrialstandstillin pages 1-3).
Thromboembolic ischemic stroke Stroke (HP:0001297); Cerebral infarction (HP:0001296) Important complication due to atrial blood stasis from absent contraction; reported in pediatric and young adult cases and used to justify anticoagulation (kato2024atrialstandstilla pages 1-3, anand2024atrialstandstillin pages 1-3, ishikawa2020cardiacemerinopathy pages 1-4).
Left ventricular noncompaction when present Left ventricular noncompaction (HP:0006677) Seen in syndromic/genetic forms, especially EMD-associated “cardiac emerinopathy,” and may compound thromboembolic risk (ishikawa2020cardiacemerinopathy pages 1-4).

Table: This table maps common atrial standstill clinical and diagnostic findings to suggested Human Phenotype Ontology terms. It is useful for structuring phenotype annotation in a disease knowledge base while preserving the diagnostic context from ECG, echocardiography, and electrophysiology studies.

Quality of life impact: Not systematically quantified in retrieved evidence. However, symptomatic bradycardia, presyncope/syncope, heart failure manifestations, and stroke are repeatedly noted as major clinical impacts, often driving permanent pacing and anticoagulation decisions (zheng2022leftbundlebranch pages 1-2, anand2024atrialstandstillin pages 1-3, kato2024atrialstandstilla pages 1-3).

4. Genetic / molecular information

4.1 Causal genes and molecular classes

The retrieved literature supports several mechanistic classes: - Voltage-gated sodium channel dysfunction (SCN5A loss-of-function) with impaired atrial excitability/conduction and progressive atrial electrical failure (tan2018ahomozygousscn5a pages 1-4, makita2005congenitalatrialstandstill pages 1-2). - Gap junction / conduction reserve modification (GJA5 connexin‑40 polymorphisms proposed as modifiers in SCN5A families) (makita2005congenitalatrialstandstill pages 1-2). - Nuclear envelope / myocyte structural integrity disorders (EMD, and broader laminopathy/EDMD context) causing progressive atrial myopathy leading to standstill and thromboembolism risk (ishikawa2020cardiacemerinopathy pages 1-4, valenti2022clinicalprofilearrhythmias pages 1-2). - Pacemaker channel association (HCN4) in familial bradyarrhythmia syndromes with atrial standstill in a reported family (anand2024atrialstandstillin pages 1-3).

4.2 Variant interpretation and population frequency

Only limited population frequency information was retrieved directly: the CAV3 p.Leu84Pro variant was reported as not observed in 6500 individuals in the NHLBI GO Exome Sequencing Project but was later reclassified as a VUS, underscoring the need for cautious interpretation (gal2017atrialstandstillin pages 1-2). Broader allele-frequency statistics (e.g., gnomAD) were not retrieved in this run.

5. Environmental information

Evidence in this run is primarily clinical; nevertheless, non-genetic contributors include metabolic derangement (hyperkalemia), drug toxicity (digitalis/quinidine), hypoxia, and ischemic/inflammatory myocardial conditions (myocarditis, MI, sarcoidosis) reported as associated causes/precipitants (agrawal2017persistentatrialstandstill pages 3-4, suzuki2019acaseof pages 3-5, kim2016atrialstandstillin pages 1-2).

6. Mechanism / pathophysiology

6.1 Causal chain (integrated model)

A consistent disease model across genetic and acquired contexts is:

Trigger/primary substrate (channelopathy; nuclear envelope myopathy; infiltrative/inflammatory disease; metabolic/drug injury) → atrial myocyte dysfunction and/or structural remodeling → atrial fibrosis/scar with low-voltage substrate → loss of atrial excitability and conduction (electrical silence; inability to pace-capture) → loss of atrial mechanical contraction (absent Doppler A waves) → blood stasis → thromboembolism/stroke; in parallel, junctional/escape rhythms and bradycardia drive symptoms and pacing need. Evidence for atrial fibrosis/structural disease (e.g., LGE in both atria) and electrical silence is reported in sarcoidosis-associated AS and in genetic cases with biatrial LGE (kim2016atrialstandstillin pages 1-2, anand2024atrialstandstillin pages 1-3).

6.2 Upstream vs downstream mechanisms

  • Upstream: genetic loss-of-function in excitability genes (SCN5A), structural myocyte-nuclear coupling defects (EMD), or inflammatory infiltration (sarcoidosis) (tan2018ahomozygousscn5a pages 1-4, ishikawa2020cardiacemerinopathy pages 1-4, kim2016atrialstandstillin pages 1-2).
  • Downstream: progressive atrial scarring/low-voltage substrate and eventual electrical silence; mechanical atrial paralysis; thromboembolism risk (suzuki2019acaseof pages 3-5, agrawal2017persistentatrialstandstill pages 3-4, kato2024atrialstandstilla pages 1-3).

6.3 Spatial progression and anatomical localization

Several reports describe progression beginning in the high/midlateral right atrium and spreading to the entire right atrium and then left atrium, with some patients retaining small islands of viable atrial tissue. A striking example is residual atrial electrical activity confined to the coronary sinus, enabling coronary-sinus atrial lead placement (suzuki2019acaseof pages 1-3, suzuki2019acaseof pages 3-5).

6.4 Suggested ontology terms for mechanisms (GO/CL/UBERON)

UBERON (anatomy): - UBERON:0000948 (heart) — general - UBERON:0002079 (right atrium) and UBERON:0002078 (left atrium) — atrial myocardium involvement - UBERON:0002347 (coronary sinus) — residual atrial activity/pacing site in partial AS cases (suzuki2019acaseof pages 1-3)

Cell Ontology (CL) (major involved cell types): - CL:0000746 (cardiac muscle cell / cardiomyocyte) - CL:0002548 (cardiac fibroblast) — fibrosis substrate (mechanistic inference consistent with atrial fibrotic substrate discussed across sources)

GO biological process (examples): - “cardiac muscle cell action potential” (GO:0086001) - “regulation of heart rate” (GO:0002027) - “cardiac conduction” (GO:0061337) - “extracellular matrix organization” (GO:0030198) - “fibroblast proliferation” (GO:0048144)

(These ontology suggestions are consistent with the electrophysiologic and fibrotic remodeling substrate described in the retrieved literature, although GO IDs are not explicitly cited in the sources.) (agrawal2017persistentatrialstandstill pages 3-4, kim2016atrialstandstillin pages 1-2, anand2024atrialstandstillin pages 1-3)

7. Anatomical structures affected

  • Primary organ: heart, specifically atrial myocardium (right and/or left atrium) (agrawal2017persistentatrialstandstill pages 1-3, suzuki2019acaseof pages 3-5).
  • Potential focal sites of residual activity: coronary sinus and limited atrial regions in partial AS (suzuki2019acaseof pages 1-3).
  • Secondary/systemic impact: brain via ischemic stroke due to thromboembolism (anand2024atrialstandstillin pages 1-3, kato2024atrialstandstilla pages 1-3).

8. Temporal development

AS may be intermittent or permanent and progressive. Several sources describe progression from partial/focal atrial involvement to diffuse standstill, often with evolving atrial scarring and eventual atrial pacing failure risk (suzuki2019acaseof pages 3-5, agrawal2017persistentatrialstandstill pages 3-4). Recovery of atrial activity is possible in select contexts, including reports of reversal with sustained atrial/AV sequential pacing after surgery and recovery after months in a pediatric case (agrawal2017persistentatrialstandstill pages 1-3, kato2024atrialstandstilla pages 1-3).

9. Inheritance and population

9.1 Epidemiology

AS is consistently described as rare, but population prevalence/incidence estimates for atrial standstill overall were not retrieved.

A partial quantitative window comes from EDMD/laminopathy-focused systematic review data (not population-wide): in EDMD/cardiolaminopathies, the incidence rate (IR) for atrial standstill ranged from 0 to 2 events per 100 patient-years in the reviewed cohorts (Biology; published 2022-03, https://doi.org/10.3390/biology11040530) (valenti2022clinicalprofilearrhythmias pages 1-2).

9.2 Inheritance patterns (genetic forms)

  • Autosomal dominant (variable penetrance): HCN4 familial bradyarrhythmia/atrial standstill presentation and SCN5A family with incomplete penetrance (anand2024atrialstandstillin pages 1-3, makita2005congenitalatrialstandstill pages 1-2).
  • Autosomal recessive/biallelic effect: Homozygous SCN5A p.Val1340Leu associated with atrial standstill and sudden death risk (tan2018ahomozygousscn5a pages 1-4).
  • X‑linked recessive: EMD-associated “cardiac emerinopathy” with affected males requiring device therapy and asymptomatic female carriers reported (ishikawa2020cardiacemerinopathy pages 1-4).

10. Diagnostics

10.1 Clinical tests and diagnostic workflow (practical)

The contemporary case literature supports a multimodal workflow: 1) ECG (absent P waves; escape rhythm) (zheng2022leftbundlebranch pages 1-2)
2) Echocardiography with Doppler/TDI (absent A wave; atrial dilation) (agrawal2017persistentatrialstandstill pages 3-4, anand2024atrialstandstillin pages 1-3)
3) Electrophysiology study / mapping to confirm atrial inexcitability and identify residual viable tissue for lead placement (suzuki2019acaseof pages 1-3, suzuki2019acaseof pages 3-5)
4) Cardiac MRI with LGE to assess atrial fibrosis and associated cardiomyopathy (biatrial LGE reported in genetic and inflammatory cases) (kim2016atrialstandstillin pages 1-2, anand2024atrialstandstillin pages 1-3)

A structured summary with MAXO-aligned intervention labels is provided here:

Intervention/test Suggested MAXO term (name and MAXO ID if known; otherwise leave blank) Indication in atrial standstill Evidence source
12-lead electrocardiogram (ECG) Electrocardiographic monitoring First-line diagnostic test; typically shows absent P waves with junctional or ventricular escape rhythm/bradycardia, helping establish electrical atrial silence (agrawal2017persistentatrialstandstill pages 1-3, anand2024atrialstandstillin pages 1-3, zheng2022leftbundlebranch pages 1-2) Agrawal et al., 2017, Annals of Noninvasive Electrocardiology; Anand et al., 2024, Journal of Arrhythmia; Zheng et al., 2022, Frontiers in Cardiovascular Medicine
Ambulatory ECG / Holter monitoring Ambulatory electrocardiographic monitoring Detects persistent bradyarrhythmia, pauses, junctional rhythm burden, and progression of atrial electrical inactivity; useful in symptomatic or pediatric cases (gal2017atrialstandstillin pages 1-2) Gal et al., 2017, HeartRhythm Case Reports
Echocardiography with Doppler (mitral/tricuspid inflow, tissue Doppler) Echocardiography Demonstrates absent mechanical atrial contraction, especially loss of A waves on transmitral/tricuspid inflow or tissue Doppler; also assesses atrial dilation/giant atrium (agrawal2017persistentatrialstandstill pages 3-4, anand2024atrialstandstillin pages 1-3, kato2024atrialstandstilla pages 1-3, zheng2022leftbundlebranch pages 1-2) Agrawal et al., 2017, Annals of Noninvasive Electrocardiology; Anand et al., 2024, Journal of Arrhythmia; Kato et al., 2024, Journal of St. Marianna University; Zheng et al., 2022, Frontiers in Cardiovascular Medicine
Electrophysiology (EP) study and electroanatomic mapping Electrophysiologic study Confirms atrial inexcitability when atria cannot be captured at high output; maps residual viable atrial tissue (often only coronary sinus or limited regions) and guides lead placement if atrial pacing is attempted (suzuki2019acaseof pages 1-3, anand2024atrialstandstillin pages 1-3, gal2017atrialstandstillin pages 1-2) Suzuki et al., 2019, HeartRhythm Case Reports; Anand et al., 2024, Journal of Arrhythmia; Gal et al., 2017, HeartRhythm Case Reports
Cardiac magnetic resonance imaging (MRI) with late gadolinium enhancement (LGE) Cardiac magnetic resonance imaging Characterizes atrial cardiomyopathy/fibrosis and associated structural disease; in reported cases showed biatrial LGE, right atrial dilation, or LV noncompaction (anand2024atrialstandstillin pages 1-3, ishikawa2020cardiacemerinopathy pages 1-4) Anand et al., 2024, Journal of Arrhythmia; Ishikawa et al., 2020, Circulation: Arrhythmia and Electrophysiology
Permanent pacemaker implantation: single-chamber ventricular pacemaker Cardiac pacemaker implantation Main symptomatic treatment for bradycardia/escape rhythm when atrial capture is absent or atrial lead placement fails; used in diffuse/persistent atrial standstill (zheng2022leftbundlebranch pages 1-2, gal2017atrialstandstillin pages 1-2) Zheng et al., 2022, Frontiers in Cardiovascular Medicine; Gal et al., 2017, HeartRhythm Case Reports
Atrial lead implantation at residual excitable tissue (e.g., coronary sinus) when feasible Cardiac pacemaker implantation Considered in partial atrial standstill if viable atrial myocardium remains; EP mapping can identify coronary sinus or localized atrial sites suitable for sensing/capture (suzuki2019acaseof pages 1-3, agrawal2017persistentatrialstandstill pages 3-4) Suzuki et al., 2019, HeartRhythm Case Reports; Agrawal et al., 2017, Annals of Noninvasive Electrocardiology
Physiologic pacing: left bundle branch area pacing (LBBAP) Physiologic cardiac pacing Alternative ventricular pacing strategy for patients needing permanent pacing, aiming to avoid dyssynchrony associated with right ventricular apical pacing; successfully implemented in atrial standstill with giant atrium (zheng2022leftbundlebranch pages 1-2, zheng2022leftbundlebranch media 3add666d) Zheng et al., 2022, Frontiers in Cardiovascular Medicine
Anticoagulation for thromboembolism prevention Anticoagulant therapy Used because absent atrial contraction causes blood stasis and raises risk of thromboembolism/stroke; particularly relevant after ischemic stroke or with atrial standstill plus LVNC/atrial enlargement (kato2024atrialstandstilla pages 1-3, anand2024atrialstandstillin pages 1-3, ishikawa2020cardiacemerinopathy pages 1-4) Kato et al., 2024, Journal of St. Marianna University; Anand et al., 2024, Journal of Arrhythmia; Ishikawa et al., 2020, Circulation: Arrhythmia and Electrophysiology

Table: This table summarizes the main diagnostic tests and management approaches reported for atrial standstill, including suggested MAXO-aligned intervention labels. It is useful for knowledge-base curation because it links each intervention to its clinical role and supporting source evidence.

10.2 Differential diagnosis (high-level)

Within retrieved evidence, AS is contrasted clinically with atrial fibrillation in that AF has fibrillatory activity rather than true atrial electrical silence; EP recordings and inability to pace-capture support AS rather than AF (suzuki2019acaseof pages 1-3, anand2024atrialstandstillin pages 1-3).

11. Outcomes / prognosis

Outcome data are sparse and are primarily case-based, but several consistent risk themes emerge: - Thromboembolism/stroke risk: 2024 pediatric/young adult cases emphasize that loss of atrial contraction “will likely cause blood flow stagnation in the atria” with highly prevalent thromboembolic complications in such settings, prompting anticoagulation strategies (kato2024atrialstandstilla pages 1-3, anand2024atrialstandstillin pages 1-3). - Need for chronic pacing: symptomatic bradycardia is common, frequently requiring permanent pacing (zheng2022leftbundlebranch pages 1-2). - Progression / pacing failure risk: progressive atrial disease can cause eventual atrial pacing failure, motivating careful follow-up and EP-guided lead strategies (suzuki2019acaseof pages 3-5, gal2017atrialstandstillin pages 1-2).

Quantitative cohort-level complication rates specific to atrial standstill (outside EDMD/laminopathy contexts) were not retrieved.

12. Treatment

12.1 Pharmacotherapy

No disease-specific pharmacologic reversal therapy is established in the retrieved evidence. However, anticoagulation is a recurring, real-world intervention for thromboembolism prevention: - A 2024 HCN4-associated case states: “The patient was started on anticoagulation therapy to prevent further thromboembolic events.” (anand2024atrialstandstillin pages 1-3) - A 2022 LBBAP case used apixaban 2.5 mg bid for embolism prevention (zheng2022leftbundlebranch pages 1-2). - A pediatric stroke case used edoxaban for secondary prevention (kato2024atrialstandstilla pages 1-3). - A post-surgical case used warfarin as postoperative medication (agrawal2017persistentatrialstandstill pages 1-3).

12.2 Device therapy (mainstay): pacemakers and lead strategies

Permanent pacing is repeatedly described as required for symptomatic bradycardia.

Standard approaches in the case literature include: - Single-chamber ventricular pacing when atrial capture is absent or atrial lead placement fails (gal2017atrialstandstillin pages 1-2, zheng2022leftbundlebranch pages 1-2). - Dual-chamber pacing with atrial lead in coronary sinus when residual atrial myocardium is present there, enabling AV sequential pacing (suzuki2019acaseof pages 3-5). - AV sequential pacing potentially reversing standstill in select postoperative contexts (agrawal2017persistentatrialstandstill pages 1-3).

Physiologic pacing development / real-world implementation: A notable technical development is the application of left bundle branch area pacing (LBBAP) in AS with a giant atrium. The 2022 case emphasizes avoidance of dyssynchrony associated with traditional RV apical pacing and reports successful LBBAP implantation with stable parameters; their figures show absent atrial activity and LBBAP capture characteristics (zheng2022leftbundlebranch media 3add666d).

12.3 Suggested MAXO terms (selected)

  • Cardiac pacemaker implantation (MAXO ID not retrieved)
  • Physiologic cardiac pacing (MAXO ID not retrieved)
  • Anticoagulant therapy (MAXO ID not retrieved)

(IDs were not available in retrieved evidence; terms are provided for knowledge-base alignment.)

12.4 Experimental treatments / clinical trials

A ClinicalTrials.gov search did not retrieve atrial-standstill-specific trials. Related bradyarrhythmia physiologic pacing trials include His bundle pacing studies (e.g., NCT03590353, NCT03685617) in slow arrhythmias, which may be relevant to pacing strategy selection but are not AS-specific in the retrieved records.

13. Prevention

No atrial-standstill-specific primary prevention strategies were identified. Secondary/tertiary prevention in retrieved evidence centers on: - Stroke prevention via anticoagulation in AS with atrial paralysis/large atria and/or prior stroke (anand2024atrialstandstillin pages 1-3, zheng2022leftbundlebranch pages 1-2, kato2024atrialstandstilla pages 1-3). - Monitoring atrial activity for progression or recovery (kato2024atrialstandstilla pages 1-3).

14. Other species / natural disease

No veterinary or non-human natural disease evidence was retrieved for atrial standstill in this run.

15. Model organisms

No atrial-standstill-specific model organism studies were retrieved.

Expert opinion and authoritative synthesis (interpretation grounded in retrieved sources)

Atrial standstill can be viewed as an end-stage atrial cardiomyopathy phenotype with a final common pathway of atrial fibrosis/low-voltage substrate and atrial paralysis, regardless of whether the upstream driver is genetic (e.g., SCN5A/EMD) or acquired (e.g., sarcoidosis, drug/metabolic injury). This framework is supported by mechanistic descriptions of progressive atrial electrogram loss, scarring, and atrial inexcitability in electrophysiology-focused case literature and by the EDMD/cardiolaminopathy systematic review emphasizing structured surveillance for atrial arrhythmias and thromboembolic prevention in high-risk genetic substrates (agrawal2017persistentatrialstandstill pages 3-4, suzuki2019acaseof pages 3-5, valenti2022clinicalprofilearrhythmias pages 1-2).

Key evidence gaps (important for knowledge-base curation)

  • MONDO and MeSH IDs for atrial standstill were not retrieved in this run; additional ontology-directed searches would be required for canonical identifiers.
  • Population-level prevalence/incidence of atrial standstill in the general population was not retrieved; available quantitative rates are primarily within EDMD/laminopathy cohorts.
  • Limited systematic data on quality of life and long-term outcomes outside case reports.

Appendix: Visual evidence (example)

In the LBBAP case report, a figure panel demonstrates absence of atrial activity (no P waves) consistent with atrial standstill alongside pacing documentation, supporting the ECG-based definition and contemporary pacing implementation (zheng2022leftbundlebranch media 3add666d).

References

  1. (zheng2022leftbundlebranch pages 1-2): Jingang Zheng, Qing-zhen Yang, Jia-sheng Zheng, Qiang Chen, and Qi Jin. Left bundle branch area pacing in a giant atrium with atrial standstill: a case report and literature review. Frontiers in Cardiovascular Medicine, Mar 2022. URL: https://doi.org/10.3389/fcvm.2022.836964, doi:10.3389/fcvm.2022.836964. This article has 3 citations and is from a peer-reviewed journal.

  2. (anand2024atrialstandstillin pages 1-3): Abhinav B. Anand, Bhavik S. Shah, Girish R. Sabnis, and Ajay U. Mahajan. Atrial standstill in a young patient with ischemic stroke associated with inheritance of a novel hcn4 mutation. Journal of Arrhythmia, 40:1519-1522, Sep 2024. URL: https://doi.org/10.1002/joa3.13150, doi:10.1002/joa3.13150. This article has 2 citations and is from a peer-reviewed journal.

  3. (agrawal2017persistentatrialstandstill pages 3-4): Harsh Agrawal, Kul Aggarwal, and Martin A. Alpert. Persistent atrial standstill following the cox‐maze iii procedure: reversal with sustained atrial pacing. Annals of Noninvasive Electrocardiology, 22:e12399, Mar 2017. URL: https://doi.org/10.1111/anec.12399, doi:10.1111/anec.12399. This article has 5 citations and is from a peer-reviewed journal.

  4. (ishikawa2020cardiacemerinopathy pages 1-4): Taisuke Ishikawa, Hiroyuki Mishima, Julien Barc, Masanori P. Takahashi, Keiichi Hirono, Shigenori Terada, Shinya Kowase, Teruki Sato, Yasushi Mukai, Yoshiaki Yui, Kimie Ohkubo, Hiroki Kimoto, Hiroyuki Watanabe, Yukiko Hata, Takeshi Aiba, Seiko Ohno, Akiko Chishaki, Wataru Shimizu, Minoru Horie, Fukiko Ichida, Akihiko Nogami, Koh-Ichiro Yoshiura, Jean-Jacques Schott, and Naomasa Makita. Cardiac emerinopathy. Circulation: Arrhythmia and Electrophysiology, Oct 2020. URL: https://doi.org/10.1161/circep.120.008712, doi:10.1161/circep.120.008712. This article has 32 citations and is from a peer-reviewed journal.

  5. (agrawal2017persistentatrialstandstill pages 1-3): Harsh Agrawal, Kul Aggarwal, and Martin A. Alpert. Persistent atrial standstill following the cox‐maze iii procedure: reversal with sustained atrial pacing. Annals of Noninvasive Electrocardiology, 22:e12399, Mar 2017. URL: https://doi.org/10.1111/anec.12399, doi:10.1111/anec.12399. This article has 5 citations and is from a peer-reviewed journal.

  6. (suzuki2019acaseof pages 3-5): Yuya Suzuki, Asumi Takei, Hiroyuki Takahara, Yayoi Taniguchi, Toru Ozawa, and Nobutaka Inoue. A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus. HeartRhythm Case Reports, 5:338-342, Jun 2019. URL: https://doi.org/10.1016/j.hrcr.2019.03.008, doi:10.1016/j.hrcr.2019.03.008. This article has 6 citations.

  7. (podolec2019clinicalclassificationof pages 2-3): Piotr Podolec, Adrian Baranchuk, Josep Brugada, Piotr Kukla, Jacek Lelakowski, Grzegorz Kopeć, Paweł Rubiś, Jakub Stępniewski, Jakub Podolec, Monika Komar, Lidia Tomkiewicz-Pająk, and Paweł Tomasz Matusik. Clinical classification of rare cardiac arrhythmogenic and conduction disorders, and rare arrhythmias. Polish archives of internal medicine, 129 3:154-159, Feb 2019. URL: https://doi.org/10.20452/pamw.4451, doi:10.20452/pamw.4451. This article has 14 citations.

  8. (kato2024atrialstandstilla pages 1-3): Tadahito Kato, Yosuke Osada, and Atsushi Kawaguchi. Atrial standstill: a rare cause of pediatric stroke and management strategies. Journal of St. Marianna University, 15:21-25, Jan 2024. URL: https://doi.org/10.17264/stmarieng.15.21, doi:10.17264/stmarieng.15.21. This article has 0 citations.

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  10. (tan2018ahomozygousscn5a pages 1-4): Reina Bianca Tan, Ivan Gando, Lei Bu, Frank Cecchin, and William Coetzee. A homozygous scn5a mutation associated with atrial standstill and sudden death. Pacing and Clinical Electrophysiology, 41:1036-1042, Jun 2018. URL: https://doi.org/10.1111/pace.13386, doi:10.1111/pace.13386. This article has 31 citations.

  11. (gal2017atrialstandstillin pages 1-2): Dana B. Gal, Julianne Wojciak, Jennifer Perera, Ronn E. Tanel, and Akash R. Patel. Atrial standstill in a pediatric patient with associated caveolin-3 mutation. HeartRhythm Case Reports, 3:513-516, Nov 2017. URL: https://doi.org/10.1016/j.hrcr.2017.07.014, doi:10.1016/j.hrcr.2017.07.014. This article has 4 citations.

  12. (kim2016atrialstandstillin pages 1-2): Tae-Hun Kim, Hyungseop Kim, Hyoung-Seob Park, Seongwook Han, and Nam-Hee Park. Atrial standstill in suspected isolated cardiac sarcoidosis. Journal of cardiology cases, 14 5:136-138, Nov 2016. URL: https://doi.org/10.1016/j.jccase.2016.06.010, doi:10.1016/j.jccase.2016.06.010. This article has 11 citations.

  13. (suzuki2019acaseof pages 1-3): Yuya Suzuki, Asumi Takei, Hiroyuki Takahara, Yayoi Taniguchi, Toru Ozawa, and Nobutaka Inoue. A case of atrial standstill with the atrial lead of a dual-chamber pacemaker implanted in the coronary sinus. HeartRhythm Case Reports, 5:338-342, Jun 2019. URL: https://doi.org/10.1016/j.hrcr.2019.03.008, doi:10.1016/j.hrcr.2019.03.008. This article has 6 citations.

  14. (valenti2022clinicalprofilearrhythmias pages 1-2): Anna Chiara Valenti, Alessandro Albini, Jacopo Francesco Imberti, Marco Vitolo, Niccolò Bonini, Giovanna Lattanzi, Renate B. Schnabel, and Giuseppe Boriani. Clinical profile, arrhythmias, and adverse cardiac outcomes in emery–dreifuss muscular dystrophies: a systematic review of the literature. Biology, 11:530, Mar 2022. URL: https://doi.org/10.3390/biology11040530, doi:10.3390/biology11040530. This article has 16 citations.

  15. (zheng2022leftbundlebranch media 3add666d): Jingang Zheng, Qing-zhen Yang, Jia-sheng Zheng, Qiang Chen, and Qi Jin. Left bundle branch area pacing in a giant atrium with atrial standstill: a case report and literature review. Frontiers in Cardiovascular Medicine, Mar 2022. URL: https://doi.org/10.3389/fcvm.2022.836964, doi:10.3389/fcvm.2022.836964. This article has 3 citations and is from a peer-reviewed journal.