Rationale: Flecainide prevents arrhythmias in catecholaminergic polymorphic ventricular tachycardia, but the antiarrhythmic mechanism remains unresolved. It is possible for flecainide to directly affect the cardiac ryanodine receptor (RyR2); however, an extracellular site of action is suggested because of the hydrophilic nature of flecainide. Objective: To investigate the mechanism for the antiarrhythmic action of flecainide in a RyR2R4496C-/- knock-in mouse model of catecholaminergic polymorphic ventricular tachycardia. Methods and Results: Flecainide prevented catecholamine-induced sustained ventricular tachycardia in RyR2R4496C-/- mice. Cellular studies were performed with isolated RyR2R4496C-/- myocytes. Isoproterenol caused the appearance of spontaneous Ca2+ transients, which were unaffected by flecainide (6 μmol/L). Flecainide did not affect Ca2+ transient amplitude, decay, or sarcoplasmic reticulum Ca2+ content. Moreover, it did not affect the frequency of spontaneous Ca2+ sparks in permeabilized myocytes. In contrast, flecainide effectively prevented triggered activity induced by isoproterenol. The threshold for action potential induction was increased significantly (P+ channel blockade. Conclusions: Flecainide prevents catecholaminergic polymorphic ventricular tachycardia in RyR2R4496C-/- mice; however, at variance with previous reports, we observed minimal effects on intracellular Ca2+ homeostasis. Our data suggest that the antiarrhythmic activity of the drug is caused by reduction of Na+ channel availability and by an increase in the threshold for triggered activity.
- ryanodine receptor
- sodium channel
- ventricular tachycardia
ASJC Scopus subject areas
- Cardiology and Cardiovascular Medicine