Variability of the QRS signal in high-resolution electrocardiograms and magnetocardiograms

The variability of electric and magnetic signals from the heart during the depolarization phase is investigated, A signal processing method is develop ed, which provides estimates for the beat-to-beat variability of the QRS-co mplex, The method is based on the decomposition of the depolarization signa l into bandpass signals by means of the Morlet wavelet transform. The beat variability of the depolarization signal is estimated by normalized varianc es of the envelope and instantaneous frequency of bandpass signals. Time in tervals of the bandpass filtered depolarization signals having a high signa l-to-noise ratio are selected applying an analysis based on phase statistic s. The method was tested by computer simulation and experimental data taken from electrocardiographic and magnetocardiographic measurements of healthy persons and patients prone to malignant ventricular tachycardia (VT) or ve ntricular fibrillation (VF). Results suggest that the calculated variance p arameters permit the characterization of beat variable depolarization signa ls and distinguish VT/VF patients from healthy persons.