Electrophysiological and Proarrhythmic Effects of Hydroxychloroquine Challenge in Guinea-Pig Hearts

Hydroxychloroquine (HCQ), clinically established in antimalarial and autoimmune therapy, recently raised cardiac arrhythmogenic concerns when used alone or with azithromycin (HCQ+AZM) in Covid-19. We report complementary, experimental, studies of its electrophysiological effects. In patch clamped HEK293 cells expressing human cardiac ion channels, HCQ inhibited I_Kr and I_K1 at a therapeutic concentrations (IC₅₀s: 10 ± 0.6 and 34 ± 5.0 microM). I_Na and I_CaL showed higher IC₅₀s; I_to and I_Ks were unaffected. AZM slightly inhibited I_Na, I_CaL, I_Ks, and I_Kr, sparing I_K1 and I_to. (HCQ+AZM) inhibited I_Kr and I_K1 (IC₅₀s: 7.7 ± 0.8 and 30.4 ± 3.0 microM), sparing I_Na, I_CaL, and I_to. Molecular induced-fit docking modeling confirmed potential HCQ-hERG but weak AZM-hERG binding. Effects of microM-HCQ were studied in isolated perfused guinea-pig hearts by multielectrode, optical RH237 voltage, and Rhod-2 mapping. These revealed reversibly reduced left atrial and ventricular action potential (AP) conduction velocities increasing their heterogeneities, increased AP durations (APDs), and increased durations and dispersions of intracellular [Ca²⁺] transients, respectively. Hearts also became bradycardic with increased electrocardiographic PR and QRS durations. The (HCQ+AZM) combination accentuated these effects. Contrastingly, (HCQ+AZM) and not HCQ alone disrupted AP propagation, inducing alternans and torsadogenic-like episodes on voltage mapping during forced pacing. O'Hara-Rudy modeling showed that the observed I_Kr and I_K1 effects explained the APD alterations and the consequently prolonged Ca²⁺ transients. The latter might then downregulate I_Na, reducing AP conduction velocity through recently reported I_Na downregulation by cytosolic [Ca²⁺] in a novel scheme for drug action. The findings may thus prompt future investigations of HCQ's cardiac safety under particular, chronic and acute, clinical situations.