Rate-dependent measures of repolarization predict inducibility of ventricular arrhythmias

The aim of this study was to compare the rate-dependent measures of repolarization in patients with and without inducible ventricular arrhythmias, and so to assess the potential arrhythmogenic role of rate-dependent heterogeneities in cardiac repolarization.

Two groups of patients were studied during invasive electrophysiological procedures for standard clinical indications. A normal group (n = 17) with supraventricular tachycardia, structurally normal hearts and no inducible ventricular arrhythmias (PES-) and an inducible group (n = 13) with inducible ventricular arrhythmias (PES+). In each patient, we delivered a series of S1-S2 pacing sequences with a baseline S2 of 500 ms, which was progressively reduced. At the same time, a 12-lead electrocardiogram (ECG) was recorded. T-waves were extracted from each ECG recording, and 12 different T-wave measures were obtained from each patient across a range of coupling intervals. These included conventional measures, and those obtained from principal component analysis (PCA) of repolarization waveforms.

At baseline S2, there was no significant difference between the PES- and PES+ using conventional T-wave measures. There were significant differences at baseline S2 between groups using PCA-derived measures. These differences showed rate dependence and were larger at shorter coupling intervals. Two dynamic ECG measurements identified subjects who were inducible during PES; maximum relative T-wave residuum >0.10 (odds ratio: 38.5, 95% CI: 4.7-318.5; P < 0.001) and maximum T-wave shape index <0.007 (odds ratio: 180.0, 95% CI: 10.2-3167.0; P < 0.001).

T-wave shape index is rate dependent and discriminates between PES- and PES+ patients. We propose that patients with inducible arrhythmias have rate-dependent heterogeneity of repolarization which could be a useful tool for risk stratification.