An Estimate of the Dispersion of Repolarization Times Based on a Biophysical Model of the ECG

Temporal heterogeneity of ventricular repolarization is a key quantity for the development of ventricular reentrant arrhythmia. In this paper, we introduce the -index, a novel ECG-based estimator of the standard deviation of ventricular myocytes´ repolarization times . Differently from other ECG metrics of repolarization heterogeneity, the -index was derived from the analysis of a biophysical model of the ECG, where repolarization is described by the dominant T-wave (DTW) paradigm. The model explains the shape of T-waves in each lead as a projection of a main waveform (the DTW) and its derivatives weighted by scalars, the lead factors. A mathematical formula is derived to link the heterogeneity of ventricular repolarization and the V-index. The formula was verified using synthetic 12-lead ECGs generated with a direct electrophysiological model for increasing values of s_θ (in the range 20-70 ms). A linear relationship between the V-index and s_θ was observed, V≈ 0.675 s_θ + 1.8 ms (R²=0.9992). Finally, 68 ECGs from the E-OTH-12-0068-010 database of the Telemetric and Holter ECG Warehouse were analyzed. The -index coherently increased after sotalol administration, a drug known to have QT-prolonging potential (p ≪ 0.001).