Beat-to-beat variability of QRS duration

Visual analysis has shown an increased beat-to-beat variability of QRS-duration (QDV) in patients with ventricular tachycardias (VT). The aim of this study was to develop an automatic algorithm for QDV analysis and to assess the contributions of high- and low-frequency components. High resolution ECGs (X,Y,Z) were recorded from 31 VT-patients and 74 healthy subjects. QRS duration was measured A) from the unfiltered signal and B) from the 40 Hz high-pass filtered vector. QDV and TDV (terminal signal variability) were calculated as the standard deviation of the duration of all normal-to-normal sequences. In the filtered ECG, VT patients had a significantly higher QDV as compared to healthy subjects (9.0±3.0 ms versus 6.7±2.2 ms). In the unfiltered analysis there was only a marginal difference. QDV was uncorrelated with heart rate variability. It is concluded that QDV and TDV are mainly related to microvariations in the high-frequency portion of the ECG, indicating variant late potentials in VT-patients