Improving the Microvolt T-Wave Alternans Peak by Changing the T-Wave Search Window Duration

The microvolt T-wave alternans (MTWA) is a risk marker for sudden death. The classical method (CM) quantifies MTWA by detecting consecutive T-wave peaks. The Hilbert Transform approach (HT) quantifies MTWA with comparable performance and relies on concatenating successive T-waves. MTWA quantification depends on the T-wave search window (TSW). This work investigated the impact of variable TSW length in HT and CM. Fourteen ECG signals from Physionet T-wave Alternans Database were analyzed. Regular QT interval (QTr) was assessed using a triangle area approach. TSW was set from 100 ms after Q-wave to 25 ms after T-wave endpoint and tapered by a straight line connecting the extremes. TSW length was recursively shortened sample-by-sample, CM and HT were applied to every TSW, and alternans peak (AP) quantified. The TSW for the maximum AP was employed to calculate a putative QT interval (QTp). Maximal AP amplitude was compared between methods by correlation analysis. QTp and QTr were compared by Friedman's test. For AP and QTp, correlations between maximal AP and QTp were respectively, 0.92 and 0.85 $(p < 0.05)$. QTr vs. QTp correlations for CM and HT were, respectively 0.71 and 0.71 $(p < 0.05)$. QTp-CM and QTp-HT were equivalent, and both larger than QTr. AP is maximized after the T-wave endpoint, indicating an optimal TSW for MTWA.