T-wave alternans spectral magnitude is sensitive to electrocardiographic beat alignment strategy

The authors studied the effect of beat alignment on the resolution of T-wave alternans (TWA). ECG leads I, avF and V1 were recorded during pacing in 23 patients, and QRS complexes aligned by (i) peak voltage, (ii) dot product, (ii) QRS fiducial, (iv) pacing artifact. TWA was computed as the T-wave power spectral sum at 0.5 cycles/beat. Fifteen patients had inducible ventricular tachycardia (VT) and 8 were non-inducible. From the latter group, 20/24 leads failed to exhibit TWA and were used to simulate alternans via a 1% augmentation of alternate STU segments. TWA was subsequently retrieved from 46%, 100%, 74% and 92% of simulations, with TWA ratios of 2.98, 5.02, 3.68, 4.49 with each alignment. Similar magnitude and sensitivity trends were seen in the VT group. Dot product beat alignment may optimize TWA detection and improve its utility in predicting VT risk