Optogenetic tachypacing facilitates burst-induced arrhythmia in stem cell-derived human atrial engineered heart tissue.

AIMS: Large animal models for atrial fibrillation (AF) research are ethically challenging and costly. Suitable humanized in vitro models could circumvent these problems. Here, we aimed to combine tissue engineering, human induced pluripotent stem cell-derived atrial cardiomyocytes (hiPSC-aCM), and optogenetic pacing to trigger an in vitro fibrillation-like state, which can be analysed by simple video recording. METHODS AND RESULTS: Atrial engineered heart tissue (aEHT) was created from hiPSC-aCM and transduced with adeno-associated virus vectors to express the channelrhodopsins CheRiff2.0, Chronos, or PsCatCh2.0f, respectively. We developed novel optogenetic hardware, based on microcontroller programmable light-emitting diodes. The interplay between aEHTs and hardware was optimized, and different pacing patterns were evaluated. Electrical burst pacing was evaluated for arrhythmia induction. Tissue constructs were analysed with regard to action potential, gene and protein expression, and structure. We found our optimized CheRiff2.0 best suitable for optogenetic pacing of aEHT at up to 5 Hz. Atrial EHT could be faithfully tachypaced at 4 Hz for 2.5 weeks. After 5 weeks, electrical burst pacing (20 Hz, 0.5 s) successfully induced self-sustained episodes of a state of fast beating, lower force, and incomplete relaxation. The propensity of these burst-evoked episodes of fibrillation was 3.2-fold higher in long-term paced aEHT than in non-paced controls. Action potential shape and gene expression recapitulated typical features of AF in the tachypaced aEHTs. CONCLUSION: We successfully created a first-of-its-kind in vitro model of AF, recapitulating the self-sustainability of atrial arrhythmia ('AF begets AF'). Fibrillation-like episodes can be verified by visual inspection, rendering analysis possible without an electrophysiological setup.