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 (APD 70 , APD 80 , APD 90 ), while ARI was measured by Wyatt and alternative meth-ods. 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 APD 90 in the endocardium and with APD 80 in the epicardium. These findings highlight the need for surface-specific approaches when estimating repolarization from electrical recordings.