Human Induced Pluripotent Stem Cell–Derived Engineered Heart Tissue as a Sensitive Test System for QT Prolongation and Arrhythmic Triggers

Background: Cardiac repolarization abnormalities in drug-induced and genetic long-QT syndrome may lead to afterdepolarizations and life-threatening ventricular arrhythmias. Human induced pluripotent stem cell–derived cardiomyocytes (hiPSC-CMs) should help to overcome the limitations of animal models based on species differences in repolarization reserve. Here, we compared head-to-head the contribution of I Ks (long QT1) and I Kr (long QT2) on action potentials (APs) in human left ventricular (LV) tissue and hiPSC-CM–derived engineered heart tissue (EHT). Methods: APs were measured with sharp microelectrodes in EHT from 3 different control hiPSC-CM lines and in tissue preparations from failing LV. Results: EHT from hiPSC-CMs showed spontaneous diastolic depolarization and AP generation that were sensitive to low concentrations of ivabradine. I Kr block by E-4031 prolonged AP duration at 90% repolarization with similar half-effective concentration in EHT and LV but larger effect size in EHT (+281 versus +110 ms in LV). Although I Kr block alone evoked early afterdepolarizations and triggered activity in 50% of EHTs, slow pacing, reduced extracellular K + , and blocking of I Kr , I Ks , and I K1 were necessary to induce early afterdepolarizations in LV. In accordance with their clinical safety, moxifloxacin and verapamil did not induce early afterdepolarizations in EHT. In both EHT and LV, I Ks block by HMR-1556 prolonged AP duration at 90% repolarization slightly in the combined presence of E-4031 and isoprenaline. Conclusions: EHT from hiPSC-CMs shows a lower repolarization reserve than human LV working myocardium and could thereby serve as a sensitive and specific human-based model for repolarization studies and arrhythmia, similar to Purkinje fibers. In both human LV and EHT, I Ks only contributed to repolarization under adrenergic stimulation.