Dispersion of repolarization in canine ventricle and the electrocardiographic T wave: Tp-e interval does not reflect transmural dispersion

BackgroundThe concept that the interval between the peak (Tpeak) and the end (Tend) of the T wave (Tp-e) is a measure of transmural dispersion of repolarization time is widely accepted but has not been tested rigorously by transmural mapping of the intact heart.ObjectivesThe purpose of this study was to test the relationship of Tp-e to transmural dispersion of repolarization by correlating local repolarization times at endocardial, midmural, and epicardial sites in the left and right ventricles with the T wave of the ECG.MethodsLocal activation times, activation-recovery intervals, and repolarization times were measured at 98 epicardial sites and up to 120 midmural and endocardial sites in eight open-chest dogs. In four of the dogs, long-term cardiac memory was induced by 3 weeks of ventricular pacing at 130 bpm because previous data suggest that, in this setting, delayed epicardial repolarization increases transmural dispersion. The other four dogs were sham operated.ResultsIn sham dogs, Tp-e was 41 ± 2.2 ms (X ± SEM), whereas the transmural dispersion of repolarization time was 2.7 ± 4.2 ms (not significant between endocardium and epicardium). Cardiac memory was associated with evolution of a transmural gradient of 14.5 ± 1.9 ms (P <.02), with epicardium repolarizing later than endocardium. The corresponding Tp-e was 43 ± 2.3 ms (not different from sham). In combined sham and memory dogs, Tp-e intervals did not correlate with transmural dispersion of repolarization times. In contrast, dispersion of repolarization of the whole heart (measured as the difference between the earliest and the latest moment of repolarization from all left and right ventricular, endocardial, intramural, and epicardial recording sites) did correlate with Tp-e (P <.0005, r = 0.98), although the latter underestimated total repolarization time by approximately 35%. The explanation for this finding is that parts of the heart fully repolarize before the moment of Tpeak.ConclusionTp-e does not correlate with transmural dispersion of repolarization but is an index of total dispersion of repolarization.