Signal processing methods for ST variability assessment in ECG

The beat-to-beat ST variability in the ECG signal is becoming an important indicator in neurocardiology. However, accurate determination of the ST variability is difficult because of uncertainty in the determination of the end point of the ST interval. T waves change their form because of breathing, heart movements, changing of lead positions etc. If the ST variability is small, as in most neurological patients, their reliable assessment is even more difficult. In this paper, we propose two methods for the assessment of the ST variability: the beat-to-beat variability of the RT interval (the time between the peak of the R wave and the peak of the T wave) and the TTs interval (the time between the peak of the T wave and the T wave point with maximal negative slope). The paper elaborates in details the method for the determination of Ts. The method is analyzed through its noise sensitivity estimation.