This study sought to investigate for an underlying genetic etiology in cases of apparent idiopathic bundle branch re-entrant ventricular tachycardia (BBRVT). BBRVT is a life-threatening arrhythmia occurring secondary to macro–re-entry within the His-Purkinje system. Although classically associated with dilated cardiomyopathy, BBRVT may also occur in the setting of isolated, unexplained conduction system disease. Cases of BBRVT with normal biventricular size and function were recruited from 6 North American centers. Enrollment required a clinically documented wide complex tachycardia and BBRVT proven during invasive electrophysiology study. Study participants were screened for mutations within genes associated with cardiac conduction system disease. Pathogenicity of identified mutations was evaluated using in silico phylogenetic and physicochemical analyses and in vitro biophysical studies. Among 6 cases of idiopathic BBRVT, each presented with hemodynamic compromise and 2 suffered cardiac arrests requiring resuscitation. Putative culprit mutations were identified in 3 of 6 cases, including 2 in SCN5A (Ala1905Gly [novel] and c.4719C>T [splice site mutation]) and 1 in LMNA (Leu327Val [novel]). Biophysical analysis of mutant Ala1905Gly Nav1.5 channels in tsA201 cells revealed significantly reduced peak current density and positive shifts in the voltage-dependence of activation, consistent with a loss-of-function. The SCN5A c.4719C>T splice site mutation has previously been reported as disease-causing in 3 cases of Brugada syndrome, whereas the novel LMNA Leu327Val mutation was associated with a classic laminopathy phenotype. Following catheter ablation, BBRVT was noninducible in all cases and none experienced a clinical recurrence during follow-up. Our investigation into apparent idiopathic BBRVT has identified the first genetic culprits for this life-threatening arrhythmia, providing further insight into its underlying pathophysiology and emphasizing a potential role for genetic testing in this condition. Our findings also highlight BBRVT as a novel genetic etiology of unexplained sudden cardiac death that can be cured with catheter ablation.

Introduction: Bundle branch reentrant ventricular tachycardia (BBRVT) is a life-threatening ventricular arrhythmia occurring secondary to macroreentry within the His-Purkinje system. Although classically associated with dilated cardiomyopathy, BBRVT may also occur in the setting of isolated, unexplained conduction system disease. Hypothesis: Idiopathic BBRVT may be secondary to genetic mutations associated with conduction system disease. Methods & Results: We identified 6 cases of BBRVT associated with normal biventricular size and function from 6 centers across North America. Study participants were screened for mutations within pre-specified genes linked to cardiac conduction system disease. Putative culprit mutations were identified in 3 of 6 cases, including 2 in SCN5A (Ala1905Gly [novel] and c.4719C>T [splice site mutation]) and 1 in LMNA (Leu327Val [novel]). Biophysical analysis of mutant Ala1905Gly Na v 1.5 channels in tsA201 cells revealed significantly reduced peak current density and positive shifts in the voltage-dependence of activation consistent with a loss-of-function. The SCN5A c.4719C>T splice-site mutation has previously been reported as disease causing in 3 cases of Brugada syndrome, while the novel LMNA Leu327Val mutation was associated with a classic laminopathy phenotype. Following catheter ablation, BBRVT was non-inducible in all cases and no clinical recurrences were observed during follow-up. Conclusions: Our investigation into apparent idiopathic BBRVT has identified the first genetic culprits for this life-threatening ventricular arrhythmia. This provides further insight into its underlying pathophysiology and emphasizes that conduction system disease, in the absence of ventricular dilation, serves as a sufficient substrate for BBRVT. Our findings also highlight BBRVT as a novel genetic etiology of unexplained sudden cardiac death that can be cured with catheter ablation.

Atrial fibrillation (AF), the most common arrhythmia, is a growing epidemic with substantial morbidity and economic burden. Mechanisms underlying vulnerability to AF remain poorly understood, which contributes to the current lack of highly effective therapies. Recognizing mechanistic subtypes of AF may guide an individualized approach to patient management. Here, we describe a family with a previously unreported syndrome characterized by early-onset AF (age <35 years), conduction disease and signs of a primary atrial myopathy. Phenotypic penetrance was complete in all mutation carriers, although complete disease expressivity appears to be age-dependent. We show that this syndrome is caused by a novel, heterozygous p.Glu11Lys mutation in the atrial-specific myosin light chain gene MYL4. In zebrafish, mutant MYL4 leads to disruption of sarcomeric structure, atrial enlargement and electrical abnormalities associated with human AF. These findings describe the cause of a rare subtype of AF due to a primary, atrial-specific sarcomeric defect.

Understanding the limitations of routine genetic testing protocols is of critical importance for the clinician. Standard DNA sequencing protocols are a reliable method for the detection of single point mutations or small insertions and deletions. However, these protocols cannot detect the presence of large genomic rearrangements that might affect culprit genes. This failure might lead to the questioning of a diagnosis, or prevent familial cascade screening. We present the first report of a large genomic duplication affecting the KCNQ1 gene in a patient with a robust phenotype of long QT syndrome who was first reported to have negative genetic results.

Background— J-wave ECG patterns are associated with an increased risk of sudden arrhythmic death, and experimental evidence supports a transient outward current (I to )-mediated mechanism of J-wave formation. This study aimed to determine the frequency of genetic mutations in genes encoding the I to in patients with J waves on ECG. Methods and Results— Comprehensive mutational analysis was performed on I to -encoding KCNA4 , KCND2 , and KCND3 genes, as well as the previously described J-wave–associated KCNJ8 gene, in 51 unrelated patients with ECG evidence defining a J-wave syndrome. Only patients with a resuscitated cardiac arrest or type 1 Brugada ECG pattern were included for analysis. A rare genetic mutation of the KCND2 gene, p.D612N, was identified in a single patient. Co-expression of mutant and wild-type KCND2 with KChIP2 in HEK293 cells demonstrated a gain-of-function phenotype, including an increase in peak I to density of 48% ( P <0.05) in the heterozygous state. Using computer modeling, this increase in I to resulted in loss of the epicardial action potential dome, predicting an increased ventricular transmural I to gradient. The previously described KCNJ8 -S422L mutation was not identified in this cohort of patients with ECG evidence of J-wave syndrome. Conclusions— These findings are the first to implicate the KCND2 gene as a novel cause of J-wave syndrome associated with sudden cardiac arrest. However, genetic defects in I to -encoding genes seem to be an uncommon cause of sudden cardiac arrest in patients with apparent J-wave syndromes.