Transmural differences in rate adaptation of repolarization duration quantified from ECG repolarization interval dynamics

Rate adaptation of repolarization duration has been shown to provide relevant information for arrhythmic risk stratification. In this work we investigate rate adaptation of QT interval, T wave width (T_w), and distance from peak to end of the T wave (T_pe), in response to step like HR changes induced during tilt test. QT and T_w presented a pronounced memory effect completed in two phases: a fast initial one and a subsequent slow accommodation (mean time for QT to complete 90% of the change was 77.0 ± 20.6 s); while T_pe, considered a measure of transmural dispersion of repolarization, presents only a fast change, practically synchronous with HR change. Based on this finding, we propose a method to indirectly compute differences in APD restitution slopes of the midmiocardial cells (¿_m) and epicardial cells (¿_e) by making only use of the surface ECG: ¿¿¿¿ = (¿_m-¿ ¿_e) = ¿T_pe/¿RR. In our study, the mean of ¿T_pe/¿RR across recordings is 0.0371 ± 0.0327 ms/ms, which are in agreement with theoretical studies in human ventricle (ten Tusscher 2006 model), where mean ¿¿ is 0.0364 for the same RR range.