Quantifying APD-ARI Differences Across Endo-Epicardial Surfaces in Human and Porcine Hearts

This study compares activation-recovery interval (ARI) from unipolar electrograms with optically derived action potential duration (APD) as the reference, across endocardial and epicardial surfaces in healthy porcine (N=3) and pathological human hearts (N=2). Optical and electrical signals were recorded simultaneously using high-speed cameras and transparent electrode arrays. APD was computed at 70-90% repolarization (APD₇₀, APD₈₀, APD₉₀), while ARI was measured by Wyatt and alternative methods. Comparisons revealed layer-dependent differences: in pigs, the Wyatt method showed the best agreement with endocardial APD, whereas the alternative method better matched epicardial APD; in humans, the alternative method yielded the closest agreement with APD₉₀ in the endocardium and with APD₈₀ in the epicardium. These findings highlight the need for surface-specific approaches when estimating repolarization from electrical recordings.