Background: Previous studies have reported a circadian variation of ventricular tachyarrhythmias. However, there is no detailed information of the daily distribution of ventricular tachycardia (VT) and ventricular fibrillation (VF) episodes. The purpose of this study was to evaluate the daily distribution of episodes of ventricular tachyarrhythmia in patients with implantable cardioverter defibrillators.
Material/Methods: We used data stored by last-generation implantable cardioverter-defibrillators (ICD) to retrospectively evaluate the circadian distribution of VT and VF in 70 patients with ICD. The distribution of tachyarrhythmias was categorized into four time zones: zone 1 (06:00–11:59), zone 2 (12:00–17:59), zone 3 (18:00–23:59), and zone 4 (00:00–05:59).
Results: During a follow-up of a mean of 3.1±1.3 years, a total of 791 ventricular arrhythmias were recorded from which 631 events were VT and 160 VF. A circadian variation of episodes of ventricular tachyarrhythmia was evident. The incidence of ventricular arrhythmia sharply increased in zone 1 (8.82±2.13, p<0.0001). Episodes of VT had peaks in zones 1 and 2 (7.44±2.03 and 2.70±0.65, p<0.001) and episodes of VF had peaks in zones 1 and 4 (1.38±0.39 and 1.30±0.51, p<0.011). No difference was observed between patients who used betablocker and those who did not.
Conclusions: Malignant venricular tachyarrhythmias have a circadian distribution. VT peaks occur in the morning and noon hours and VF peaks occurs at the night and morning hours. Betablocker and/or amiodarone usage do not alter this distribution.

Keywords: Amiodarone - pharmacology, Circadian Rhythm - physiology, Defibrillators, Implantable, Tachycardia, Ventricular - physiopathology