Circadian variation of sustained ventricular tachyarrhythmias terminated by appropriate shocks in patients with an implantable cardioverter defibrillator.

To determine the circadian variation of sustained ventricular tachyarrhythmias, 78 consecutive patients with an implanted cardioverter defibrillator were analyzed with regard to the occurrence of spontaneous shock episodes during a mean follow-up period of 18 +/- 12 months. In 39 patients 207 shock episodes that terminated potentially life-threatening ventricular tachyarrhythmias could be related to an exact time of onset. A circadian variation (p < 0.001) of these events was demonstrated, with a primary morning peak between 7 hours and 11 hours and a secondary, much smaller peak between 16 hours and 20 hours. This finding indicates the relevance of endogeneous or exogeneous triggers in the cause of malignant arrhythmias that potentially lead to sudden cardiac death. Subgroup analyses revealed an association of the circadian pattern to the New York Heart Association functional classification, indicating perhaps a different role of triggers in different patient populations.