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

Abstract

The presence of myocardial ischemia can increase ventricular arrhythmic risk due to a raised dispersion of ventricular repolarization. This is reflected on the morphology of the T-wave on the electrocardiogram (ECG), and can be quantified by time-warping based indexes, like dw. However, T-wave morphology can also be affected by ischemia-induced ST segment changes, impacting the accuracy of dw. We hypothesize that ischemia-induced repolarization dispersion can be better quantified by restricting dw to the T-wave peak-to-end (T pe) interval. 101 ECG recordings from patients undergoing a percutaneous coronary intervention (PCI) were analyzed together with their control ECG recordings, acquired before the intervention. A series of dw values was calculated by quantifying the T pe morphological variations between the T-waves from the PCI and a reference derived from the control ECG recordings. We proposed a normalized version of dw, Rd, reflecting relative variations of dw during PCI to control recordings, and compare it with traditional indices behaviour. Values of dw followed a gradually increasing trend as PCI inflation time progressed, reaching a median[range] Rd value of 9.44 [1.01, 80.74] at the occlusion end. During control recordings, dw remained stable, with a low intra-patient standard deviation, range [0.02, 2.09] ms and a median[range] Rd of 1.00 [0.03, 2.93]. Rd at oclussion 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 dw showed distinct distributions depending on the occluded artery, suggesting a relation with the ischemia location. The relative variation R with ischemia of index dw (9.4) is greater than for traditional T wave amplitude (7.7), T peak-to-end interval (2.7) and T width (3.0). The index dw, quantifying T pe morphology variations, allows to follow the ischemia induced variations in repolarization in a more robust manner than classical indexes, avoiding ST segment and early T wave distortions not related to repolarization dispersion, and warranting further clinical studies to evaluate its ventricular arrhythmia risk predictive value during ischemia.