Sequences of early and late phases of repolarization on dog ventricular epicardium

Monophasic action potentials from 32 to 43 epicardial sites were recorded with concentric suction electrodes in 11 dogs during atrial pacing at a constant rate. The duration of action potentials and the sequence of repolarization referenced to the onset of ventricular activation at 50% of the highest plateau amplitude and the end of the action potential were determined. These quantities were correlated with activation sequence determined from action potential upstrokes. On the anterior ventricular surface, both 50% and 100% repolarization sequences were qualitatively similar to activation sequence and showed positive correlation coefficients. On the posterior ventricular surface, 50% and 100% repolarization sequences had little qualitative resemblance to activation sequence and showed lower correlation coefficients. Correlations between the patterns of 100% repolarization and action potential duration were significantly higher on the posterior than the anterior ventricular surface. These findings demonstrate that activation sequence has less influence on repolarization sequence on the posterior than the anterior wall and that action potential duration is the major determinant of repolarization sequence on the posterior wall. These findings extend previous descriptions of the normal sequence of ventricular repolarization and the relative roles of activation and action potential duration in determining that sequence. The study also showed differences between the sequences of 50% and 100% repolarization suggesting different slopes of action potential downstrokes at various ventricular sites with steeper slopes at the posterior basal and upper anterolateral left ventricular wall. This finding adds new detail to previous descriptions of the distribution of intrinsic ventricular recovery properties.