Time-Warping Analysis of the T-Wave Peak-to-End Interval to Quantify Ventricular Repolarization Dispersion During Ischemia.

Abstract

Variations in the dispersion of ventricular repolarization can be quantified by T-wave time-warping based index, d_w. However, the early phase of the T-wave can be affected by ST-segment changes during ischemia. We hypothesized that restricting d_w to the T-wave peak-to-end ( T_pe) would circumvent this limitation while still quantifying variations in repolarization dispersion. A total of 101 ECG recordings from patients undergoing coronary occlusion, together with their control recordings, were analyzed. A series of d_w values was calculated by quantifying the T_pe morphological variations between the T-waves at different occlusion stages and a baseline T-wave. We introduced a normalized version of d_w, R_d, reflecting variations of d_w during occlusion relative to control recordings ( R_d = 1 corresponds to the same level of variation). The d_w series followed a gradually increasing trend with occlusion time, reaching median [range] R_d values of 9.44 [1.01, 80.74] at the occlusion end. R_d at occlusion end was significantly higher than threshold values of 1, 2, 5, and 10 in 94.1%, 85.11%, 64.4% and 48.5% of patients, respectively. The spatial lead-wise analysis of d_w showed distinct distributions depending on the occluded artery, suggesting a relation with the ischemia location. The relative variation R with ischemia of index d_w (9.4) is greater than that of the T-wave amplitude (7.7), T_pe interval (2.7) and T-wave width (3.0). In conclusion, d_w tracks ischemic-induced variations in repolarization dispersion in a more robust manner than classical indexes, avoiding the impact of ST segment elevation/depression or early T-wave distortions, thus warranting further clinical studies.