Circadian variability of ventricular tachycardia QRS duration, in ICD patients with dilated cardiomyopathy

The capability of the contemporary devices to digitize and store the EGM has been utilized in tachycardia diagnosis and characterization. Automatic EGM width measurement during episodes of ventricular tachycardias (VT) is a new technical advance. Aim of the study is to investigate the circadian behavior of VT QRS variability in patients (pts) with dilated cardiomyopathy (DCM) in whom an ICE (Medtronic 7223) was implanted. Ten pts (8M, 2F, 69+/- 5 years) with DCM were included in the study. In the VT detection algorithm the EGM (far field) width criterion was programmed "passive". We evaluated 146 episodes of VT. As an index of QRS duration variability we considered the coefficient of variance (CV= SD/meanX100) of the width of the last 8 VT QRS complexes. We compared the CV of the QRS width of all the VT episodes during day versus night time. 102 VT episodes occurred during the day and 44 during the night. The mean VT cycle length recorded during the day and night time was 375+/- 32 ms and 398+/- 27 ms respectively (p=NS). The mean value of CV of the QRS duration during the day and night time was 15.1+/- 2.8 and 16.1+/- 2.7 respectively (p=0.03). In conclusion there is a circadian variability in the VT QRS duration in pts with DCM. The VT QRS duration is less stable during the night compared to the day time. It is possible that the nychtamer alterations of the sympathovagal balance modifies the electrophysiological properties of the arrhythmogenic substrate.