BEAT-TO-BEAT WAVELET VARIANCE OF THE QRS COMPLEX AS A MARKER OF ARRHYTHMOGENIC SUBSTRATE IN VENTRICULAR-TACHYCARDIA PATIENTS

This study proposes a wavelet transform based technique to assess the beat-to-beat variation of the QRS signal in post-myocardial infarction patients with sustained monomorphic ventricular tachycardia. Recent e lectrophysiological investigations suggested that the diminished synch rony between the normal myocardium and the scarred arrhythmogenic tiss ue bordering a myocardial infarction area gives rise to beat-variable ECG signal components. Using a mathematical model of small variations in a largely repetitive waveform, we show that the inherent alignment errors (trigger jitter) of the high-resolution ECG (HRECG) can artific ially increase the value of the time-domain beat-to-beat variance, mak ing it less valuable as a marker of beat-variable signal components. T o overcome this drawback, we propose the wavelet based approach which discriminates between the different factors responsible for the beat v ariability (the alignment error and the beat-variable signal component s). The Morlet wavelet transform is performed on HRECG signals from no rmal individuals (control group) and postmyocardial infarction patient s with documented ventricular tachycardia. Electrical variability is q uantitatively assessed via the beat-to-beat wavelet variance measureme nts. A marker of arrhythmogenic induced variance which achieves a good performance in discrimination of ventricular tachycardia patients fro m normal subjects was found between 200 Hz and 300 Hz. This finding is in agreement with the proposed mathematical model which states that t he useful part of the time-frequency map is shifted upward in a precis e mathematical way, as the variance induced by the beat-variable arrhy thmogenic signals depend on the frequency characteristics of the first derivative of these signals. We conclude that the dynamics of the arr hythmogenic substrate as revealed by the beat-to-beat wavelet variance can be a new estimator of ventricular tachycardia risk.