Flecainide prevents catecholaminergic polymorphic ventricular tachycardia in mice and humans

Abstract

Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited arrhythmia syndrome in which drug therapy is often ineffective. We discovered that flecainide prevents arrhythmias in a mouse model of CPVT by inhibiting cardiac ryanodine receptor-mediated Ca(2+) release and thereby directly targeting the underlying molecular defect. Flecainide completely prevented CPVT in two human subjects who had remained highly symptomatic on conventional drug therapy, indicating that this currently available drug is a promising mechanism-based therapy for CPVT.

Figure 1

Flecainide inhibits RyR2 Ca²⁺ release channels, reduces spontaneous Ca²⁺ release events and triggered beats and prevents ventricular tachycardia in a CPVT mouse model. (a) Representative examples of the activity of single sheep RyR2 channels incorporated in lipid bilayers in response to 0, 5 and 10 μM flecainide followed by washout. C, closed; O, open. (b) Average concentration dependence of flecainide's effect on RyR2 open probability (P_o), mean open time (T_o) and mean closed time (T_c). Data are expressed relative to values at 0 μM flecainide, with absolute P_o = 0.12 ± 0.07, T_o = 13.5 ± 4.4 ms and T_c = 146 ± 56 ms. RyR2 channels were activated by 1 mM Ca²⁺ on the trans (luminal) side with cis (cytosolic) at 0.0001 Ca²⁺ mM (to model resting Ca²⁺ concentration). n = 3–8 experiments per concentration; *P < 0.02, **P < 0.01 and ***P < 0.001. (c,d) Effects of flecainide on isoproterenol (ISO)-stimulated Casq2^−/− myocytes. (c) Representative examples of spontaneous sarcoplasmic reticulum Ca²⁺ release events (*) and triggered beats (†). F_ratio, Fura-2 fluorescence ratio, which is proportional to free intracellular Ca²⁺ concentration (see Supplementary Methods online). (d) Flecainide (6 μM, >10 min incubation) significantly decreased spontaneous sarcoplasmic reticulum Ca²⁺ release events and triggered beats (n = 44 cells) compared to vehicle (n = 45 cells). **P = 0.0078 and ***P < 0.001. (e) Cartoon illustrating the dual mechanism of flecainide action: (1) inhibition of the sarcoplasmic reticulum Ca²⁺ release (*) that causes delayed after depolarizations and (2) inhibition of the premature beats (†) that are triggered by delayed after depolarizations. (f) Heart rate response to ISO (1.5 mg kg⁻¹) challenge in a Casq2^−/− mouse. As illustrated in the ECG trace, the rapid and irregular heart rate (HR) was the result of numerous repetitive ventricular extrasystoles (VE, arrows) and the induction of ventricular tachycardia (VT). b.p.m., beats per minute. (g) Heart rate of the same mouse after it received flecainide (20 mg kg⁻¹) 15 min before ISO challenge. All data are means ± s.e.m.; for experimental protocols and statistical analysis see Supplementary Methods. Animal experiments were approved by the Vanderbilt University Medical Center Institutional Animal Care and Use Committee.

Figure 2

Flecainide treatment prevents exercise-induced ventricular arrhythmia in two subjects with CPVT refractory to conventional drug therapy. (a–d) Effect of flecainide treatment in a 12-year-old boy (subject 1) with a CASQ2 mutation (a,b) and in a 36-year-old female (subject 2) with an RYR2 mutation (c,d). Top of each panel, representative ECGs recorded during maximum stress; bottom of each panel, heart rate and rate of ventricular extrasystoles during an exercise test. Blue area indicates arrhythmia burden. Exercise protocol and ventricular extrasystole analysis are as previously described. Drug therapy during each exercise test: metroprolol 100 mg d⁻¹ plus verapamil 120 mg d⁻¹ (a), metroprolol 100 mg d⁻¹ plus flecainide 150 mg d⁻¹ for 7 weeks (b), bisoprolol 5 mg d⁻¹ plus verapamil 240 mg d⁻¹ (c) or flecainide 150 mg d⁻¹ for 8 weeks (d). Experiments involving human subjects were reviewed and approved by the University of Amsterdam Academic Medical Center Institutional Medical Ethical Review Board. Both human subjects (or their parents) provided informed consent.