Data processing and analysis
In each epicardial lead, activation time (AT) and end of repolarization time (RT) were determined as dV/dt minimum during QRS-complex and dV/dt maximum during T-wave, respectively, in respect to a QRS-complex onset. As a surrogate for action potential duration, activation-repolarization interval (ARI) was calculated as the difference between RT and AT. Average duration of ARI from all leads was used in analysis. A time of epicardial activation breakthrough reflecting the duration of conduction via conduction system was taken as the minimal AT throughout all epicardial leads. A duration of epicardial activation serving as an indirect estimate for activation of ventricular contractile myocardium was calculated as the difference between the maximal and minimal ATs throughout all epicardial leads. The maximal epicardial AT was used as a measure of total duration of ventricular activation. Dispersion of repolarization (DOR), a prerequisite for the unilateral conduction block, was taken as the difference between the maximal and minimal values of RTs. The inducibility of episodes of ventricular tachycardia and/or ventricular fibrillation (VT/VF) induced by burst pacing was analyzed.