Circadian variations of ventricular tachyarrhythmias detected by the implantable cardioverter-defibrillator.

OBJECTIVE: The purpose of this study was to prospectively evaluate the daily distribution of episodes of ventricular tachyarrhythmias triggering a last-generation ICD implanted in survivors of cardiac arrest not receiving any antiarrhythmic drug. BACKGROUND: Previous studies reported a circadian variation of out-of-hospital sudden cardiac arrest. Survivors of cardiac arrest and patients with sustained ventricular tachyarrhythmias have a higher risk of recurrence, but there is a lack of detailed information on the daily distribution of ventricular arrhythmia capable of precipitating the recurrence of a malignant ventricular event. METHODS: We used the data stored by a last-generation implantable cardioverter-defibrillator (ICD) to prospectively evaluate circadian distribution of ventricular tachyarrhythmias in 30 survivors of cardiac arrest, implanted with an ICD during an antiarrhythmic drug-free period. RESULTS: During a follow-up of 475 +/- 127 days, a total of 571 ventricular arrhythmias was recorded. Of these stored events, 39 episodes were ventricular fibrillation (VF), 428 events were ventricular tachycardia (VT) and the remaining 104 device activations were VTs spontaneously terminating before device therapy. A circadian variation (p < 0.001) of episodes of ventricular tachyarrhythmias was evident. The incidence of ventricular arrhythmias sharply increased at 6 a.m. and reached a maximum 4 hours later, after which there was a short decline and then a small peak between 3 p.m. and 5 p.m. With respect to different arrhythmias, VF or VTs with a cycle length < or = 350 msec demonstrated a circadian variation. Instead, VTs with a cycle length longer than 350 msec or spontaneously terminating before device discharge had a more even distribution throughout the day. In addition, most of the VF or VTs with a cycle length < or = 350 msec occurred within a few hours after awakening, which was not the case for VTs with a cycle length longer than 350 msec. CONCLUSIONS: The data of this study clearly show the existence of different circadian variations in the occurrence of ventricular tachyarrhythmias, suggesting complex interactions between the autonomic nervous system, ventricular electrophysiological properties and the onset of arrhythmia.