Spatial profiles of electrical mismatch determine vulnerability to conduction failure across a host-donor cell interface.

BACKGROUND Electrophysiological mismatch between host cardiomyocytes and donor cells can directly affect the electrical safety of cardiac cell therapies; however, the ability to study host-donor interactions at the microscopic scale in situ is severely limited. We systematically explored how action potential (AP) differences between cardiomyocytes and other excitable cells modulate vulnerability to conduction failure in vitro. METHODS AND RESULTS AP propagation was optically mapped at 75 μm resolution in micropatterned strands (n=152) in which host neonatal rat ventricular myocytes (AP duration=153.2±2.3 ms, conduction velocity=22.3±0.3 cm/s) seamlessly interfaced with genetically engineered excitable donor cells expressing inward rectifier potassium (Kir2.1) and cardiac sodium (Na(v)1.5) channels with either weak (conduction velocity=3.1±0.1 cm/s) or strong (conduction velocity=22.1±0.4 cm/s) electrical coupling. Selective prolongation of engineered donor cell AP duration (31.9-139.1 ms) by low-dose BaCl2 generated a wide range of host-donor repolarization time (RT) profiles with maximum gradients (∇RT(max)) of 5.5 to 257 ms/mm. During programmed stimulation of donor cells, the vulnerable time window for conduction block across the host-donor interface most strongly correlated with ∇RT(max). Compared with well-coupled donor cells, the interface composed of poorly coupled cells significantly shortened the RT profile width by 19.7% and increased ∇RT(max) and vulnerable time window by 22.2% and 19%, respectively. Flattening the RT profile by perfusion of 50 μmol/L BaCl2 eliminated coupling-induced differences in vulnerability to block. CONCLUSIONS Our results quantify how the degree of electrical mismatch across a cardiomyocyte-donor cell interface affects vulnerability to conduction block, with important implications for the design of safe cardiac cell and gene therapies.