Short communication: flecainide exerts an antiarrhythmic effect in a mouse model of catecholaminergic polymorphic ventricular tachycardia by increasing the threshold for triggered activity.

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 RyR2(R4496C+/-) knock-in mouse model of catecholaminergic polymorphic ventricular tachycardia. METHODS AND RESULTS Flecainide prevented catecholamine-induced sustained ventricular tachycardia in RyR2(R4496C+/-) mice. Cellular studies were performed with isolated RyR2(R4496C+/-) myocytes. Isoproterenol caused the appearance of spontaneous Ca(2+) transients, which were unaffected by flecainide (6 μmol/L). Flecainide did not affect Ca(2+) transient amplitude, decay, or sarcoplasmic reticulum Ca(2+) content. Moreover, it did not affect the frequency of spontaneous Ca(2+) sparks in permeabilized myocytes. In contrast, flecainide effectively prevented triggered activity induced by isoproterenol. The threshold for action potential induction was increased significantly (P<0.01), which suggests a primary extracellular antiarrhythmic effect mediated by Na(+) channel blockade. CONCLUSIONS Flecainide prevents catecholaminergic polymorphic ventricular tachycardia in RyR2(R4496C+/-) mice; however, at variance with previous reports, we observed minimal effects on intracellular Ca(2+) 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.