Efficacy of Flecainide in Catecholaminergic Polymorphic Ventricular Tachycardia Is Mutation-Independent but Reduced by Calcium Overload

Abstract

Background The dual Na + and cardiac Ca 2+ -release channel inhibitor, Flecainide (FLEC) is effective in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT), a disease caused by mutations in cardiac Ca 2+ -release channels (RyR2), calsequestrin (Casq2), or calmodulin. FLEC suppresses spontaneous Ca 2+ waves in Casq2-knockout (Casq2 −/− ) cardiomyocytes, a CPVT model. However, a report failed to find FLEC efficacy against Ca 2+ waves in another CPVT model, RyR2-R4496C heterozygous mice (RyR2 R4496C+/− ), raising the possibility that FLEC efficacy may be mutation dependent. Objective To address this controversy, we compared FLEC in Casq2 −/− and RyR2 R4496C+/− cardiomyocytes and mice under identical conditions. Methods After 30 min exposure to FLEC (6 μM) or vehicle (VEH), spontaneous Ca 2+ waves were quantified during a 40 s pause after 1 Hz pacing train in the presence of isoproterenol (ISO, 1 μM). FLEC efficacy was also tested in vivo using a low dose (LOW: 3 mg/kg ISO + 60 mg/kg caffeine) or a high dose catecholamine challenge (HIGH: 3 mg/kg ISO + 120 mg/kg caffeine). Results In cardiomyocytes, FLEC efficacy was dependent on extracellular [Ca 2+ ]. At 2 mM [Ca 2+ ], only Casq2 −/− myocytes exhibited Ca 2+ waves, which were strongly suppressed by FLEC. At 3 mM [Ca 2+ ] both groups exhibited Ca 2+ waves that were suppressed by FLEC. At 4 mM [Ca 2+ ], FLEC no longer suppressed Ca 2+ waves in both groups. Analogous to the results in myocytes, RyR2 R4496C+/− mice ( n = 12) had significantly lower arrhythmia scores than Casq2 −/− mice ( n = 9), but the pattern of FLEC efficacy was similar in both groups (i.e., reduced FLEC efficacy after HIGH dose catecholamine challenge). Conclusion FLEC inhibits Ca 2+ waves in RyR2 R4496C+/− cardiomyocytes, indicating that RyR2 channel block by FLEC is not mutation-specific. However, FLEC efficacy is reduced by Ca 2+ overload in vitro or by high dose catecholamine challenge in vivo , which could explain conflicting literature reports.

Flecainide in Ventricular Arrhythmias: From Old Myths to New Perspectives

“…The two main genotypes are CPVT1 (Mutations in RYR2) and CPVT2 (Mutations in the calsequestrin isoform 2 gene CASQ). Several studies demonstrated that in CPVT-patients flecainide added to beta blockers reduces clinical events, exercise-induced ventricular arrhythmias and defibrillator shocks, with good tolerance, independently from the genotype and even in genotype negative patients [61][62][63][64][65]. Flecainide should be added to betablockers in case of recurrent syncope or bidirectional VT with a class I recommendation in the American guidelines and a class IIA recommendation in the European guidelines (Table 1).…”

Role of microRNA‑129 in cancer and non‑cancerous diseases (Review)

“…Since GRIN2D is considered a key regulator of Ca 2+ influx, its expression is closely linked to cytoplasmic Ca 2+ content (10). Calmodulin 1 (CALM1) and Ca 2+ /calmodulin-dependent protein kinase II δ (CaMKIIδ), the key downstream activators of the Ca 2+ pathway in cardiomyocytes, have been linked to myocardial cell death, cardiomyopathy and HF (95,96). Therefore, GRIN2D overexpression caused Ca 2+ overload, leading to excessive activation of CALM1 and CaMKIIδ, and eventually deteriorating HF (92).…”

Molecular Mechanism and Current Therapies for Catecholaminergic Polymorphic Ventricular Tachycardia

“…Several follow-up studies attempted to reconcile this discrepancy. Evidence has been provided that flecainide is effective in reducing DCR in cells harboring the RyR2 R4496C +/− mutation, but this effect could be masked by experimental conditions such as Ca overload [93]. On the other hand, more convincing evidence comes from a recent study that employed a synthesized analog of flecainide with reduced inhibition on RyR2 activity but unaltered inhibition on Na channel [94].…”