Abstract Body: Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a potentially lethal inherited arrhythmia syndrome, with 60–80% of cases caused by pathogenic variants in ryanodine receptor 2 (RYR2). Flecainide has emerged as an effective therapy for CPVT in combination with β-blockers, yet some patients continue to experience breakthrough arrhythmias despite therapeutic drug levels.
We hypothesized that variability in flecainide responsiveness associated with the RYR2-G3946S variant may be influenced by genetic modifiers beyond the mutation itself.
To test this hypothesis, we generated two complementary human induced pluripotent stem cell (hiPSC) models. Patient-derived hiPSCs (CPVT_P) harboring the RYR2-G3946S mutation were compared with an isogenic gene-edited line (CPVT_E) carrying the same mutation in a wild-type (WT) background. Following differentiation into hiPSC-derived cardiomyocytes (hiPSC-CMs), calcium signaling was assessed by calcium wave propagation in anisotropic microtissues and calcium transients in single cells.
Under β-adrenergic stimulation, CPVT_E and CPVT_P microtissues exhibited reduced calcium wave propagation velocity and increased spatial dispersion compared with WT, consistent with increased vulnerability to reentry, and these abnormalities were not rescued by flecainide. At the single-cell level, abnormal calcium release events (aCREs) were increased in CPVT_E and CPVT_P cells compared with WT at baseline and further increased under adrenergic stress. Flecainide reduced aCRE frequency in CPVT_E cardiomyocytes (13.79 ± 15.50 at 0 μM vs 4.41 ± 7.18, 5.16 ± 4.86, and 5.65 ± 6.42 at 0.5–2 μM; n ≥ 126 cells; p < 0.001) but had no effect in CPVTP cells (n ≥ 79 cells), consistent with the patient’s clinical nonresponsiveness.
These findings indicate that flecainide responsiveness associated with the RYR2-G3946S variant is modulated by genetic modifiers in the patient background, and that abnormal calcium release events may serve as cellular indicators of arrhythmia susceptibility and predictors of therapeutic response.