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. dy 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 dy 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.