Heterogeneity of ventricular repolarisation morphology measured using orthogonal time-scale decomposition of the surface ECG

Recent findings on the contribution of cardiac M-cells in the ventricular repolarization abnormalities generate new interest for analyzing the T-wave morphology. Spatial heterogeneity of the morphology of T-wave may reflect the non-uniform recovery of ventricular excitability contributing to lower threshold for ventricular arrhythmias. The authors investigated a new approach for the analysis of the repolarization based on an orthogonal wavelet transformation of the ventricular repolarization. An index of morphological dissimilarity (IMD) measuring the differences in the distribution of energy in time and frequency domains was used to identify changes in the repolarization process. This method was evaluated under simulated condition and then applied to three populations of healthy subjects, LQTS carriers and non-carriers. The results have shown that IMD parameter is able to quantify morphological changes between leads and have an increase value when T-wave is biphasic, has notches or a U wave. Baseline wandering was not affecting IMD but noise level was increasing IMD values mainly for low-amplitude T-waves. IMD was higher in carrier LQTS patients than in non-carriers (9.5/spl plusmn/2.6 mV/sup 2/ vs. 5.0/spl plusmn/3.6 mV/sup 2/, p<0.0001) indicating that our method could be a new non-invasive parameter for quantifying abnormalities of the repolarization segment.