Abstract
Pharmacotherapy for atrial fibrillation (AF) is confounded by ventricular proarrhythmia. Vernakalant (VER) belongs to a class of atrial selective channel blockers developed in attempts to convert AF safely. Yet, robust analysis of the effects of VER in human based tissues has not been performed. We hypothesized that engineered heart tissues (EHT) composed of atrial (A) or ventricular (V) human iPSCs would provide a robust platform for quantitative analysis of chamber specific electrophysiological (EP) effects of VER. Methods: iPSCs were differentiated into cardiomyocytes using biphasic Wnt signaling, insulin, and lactate purification. Atrial-like myocytes were enriched by adding 0.75 μM retinoic acid on days 4-6 to promote atrial gene expression and specification. Myocytes were seeded onto cryosectioned, laser cut and decellularized myocardial tissues and cultured under isometric conditions. EHTs were stained with high dose, water soluble di-2-ANEPEQ to enhance signal-to-noise while avoiding toxicity. Results: Staining with 25 μM di-2-ANEPEQ provided high fidelity optical AP signals that allowed comprehensive characterization of the EP substrate. A-EHT exhibited significantly shorter AP durations than V-EHT reflecting greater repolarizing drive (APD80, 180 ms vs 367 ms; p < 0.0001, n = 4-5). Consistent with its role as an atrial-selective blocker, VER increased APD80 only in A-EHTs (180 ms vs 258 ms, p = 0.0027, n = 5). This beneficial property for combatting AF was countered by marked slowing of A-EHT conduction and AP upstroke velocity (20.6 cm/s vs 11.7 cm/s, p = 0.027, n = 5). Conclusions: Optical mapping of chamber specific EHTs confirms atrial specific nature of VER as an atrial repolarization prolonging agent but raises unexpected concerns regarding potential proarrhythmic toxicity related to atrial conduction slowing.
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