An Index for T-wave Pointwise Amplitude Variability Quantification

The comparison between the pointwise amplitude of different T-waves provides insight into ventricular repolarization liability. However, T-wave pointwise amplitude variability can be confounded by time-domain variability. We, first, compared two algorithms for removing (warping) time-domain variability, one using the original and another one using a transformed T-wave (SRSF). We, next, compared the robustness against noise of two markers, d(y) and d(a), of pointwise amplitude variability, after warping the underlying temporal variability with the preferred warping algorithm. d(y) was obtained from the transformed T-waves while d(a) was proposed in this work and was derived from the original T-waves. We, finally, used the most robust marker to measure the T-wave pointwise amplitude variability between every T-wave recorded during a Tilt test and their mean T-wave. Results showed that the preferred warping algorithm was the SRSF because it is not affected by differences between the amplitudes of the original T-waves. In addition, the marker d(a) presented lower relative error values than d(y) for every level of noise. The analysis of electrocardiogram records showed that d(a) was significantly lower during the tilt than in supine position (5.5 % vs 6.5 %, p<0.01). In conclusion, d(a) robustly quantifies physiological variabilities of the T-wave amplitude, showing its potential to be used as an arrhythmic risk predictor in future clinical situations.