Modeling cardiac electrical activity using cardiac organoids for drug screening.

Arrhythmia is one of the leading causes of mortality and lacks diagnostic and therapeutic options. Electrical activity at the cellular level is difficult to use as a basis for evaluating drug effects on cardiac rhythm. Cardiac organoids, as organized and functional cell clusters, offer significant advantages as models for the pathophysiological mechanisms of arrhythmia or as drug screening platforms. Here, we applied a standardized set of electrophysiological techniques to integrate electrophysiological activity of cardiac organoids, including multielectrode array (MEA), calcium signal optical mapping and patch clamp analysis. We first established cardiac organoids containing cardiomyocyte and endothelial cell components through hiPSC (human induced pluripotent stem cell) induction. Then by this electrophysiological detection protocol, we found that the characteristics of electrical activity and calcium transient signal of cardiac organoids under E-4031, cisapride or ATX-II induction were more similar to cardiac tissue rather than to cardiomyocytes cultured in vitro. Finally, the patch clamp analysis revealed the existence of subpopulations of ventricular-like cardiomyocytes with different electrical activity phenotypes in cardiac organoids, which aligns with the theoretical basis for cardiac rhythm formation. Our findings systematically validated the tissue-like characteristics of cardiac organoids and can be applied to the testing of molecules' effects on cardiac rhythm, thereby screening for novel antiarrhythmic drugs.