Bundle Branch Re-Entrant VentricularTachycardia: Novel Genetic Mechanisms in a Life-Threatening Arrhythmia.

Abstract

This study sought to investigate for an underlying genetic etiology in cases of apparent idiopathic bundlebranch 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 conductionsystem disease. Pathogenicity of identified mutations was evaluated using in silico phylogenetic and physicochemical analyses and invitro 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 shiftsin the voltage-dependence of activation, consistent with a loss-of-function. The SCN5A c.4719C>T splice sitemutation 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 potentialrole for genetic testing in this condition. Our findings also highlight BBRVT as a novel genetic etiology ofunexplainedsudden cardiac death that can be cured with catheter ablation.