T-Wave Alternans Ranking: Striking Disagreement between Two Vectorcardiographic Measures of Repolarization Heterogeneity

In an attempt to study the importance of T-wave feature selection for T-wave alternans (TWA) analysis, we compared the alternans in two vectorcardiographic variables: maximal T-loop vector (MaxT) and the T-loop vector integral (Ti). We analyzed TWA in the 72 standard 12-lead ECGs comprised in the Physionet TWA Challenge Database with our research ECG/VCG processing program LEADS. We computed TWA by taking the absolute differences of the even and odd averaged beat values of Ti and MaxT (MaxT-TWA and Ti-TWA); also percentual alternans (%MaxT-TWA and %Ti-TWA) was computed. Finally, we computed both the Pearson and Kendall tau-b correlation coefficients between the MaxT-TWA and Ti-TWA, and between %MaxT-7'WA and %Ti-TWA. All correlation coefficients differed significantly (P<0.01) from zero, but were relatively low (R=0.333-0.663). We conclude that T-wave features contain only in part common information; the selection of the T-wave feature in which TWA is computed deserves more attention.