Modification of the circadian pattern of ventricular tachyarrhythmias by beta-blocker therapy

BACKGROUND

Sudden cardiac death exhibits a circadian variation and predominantly occurs during morning hours, Beta-adrenergic antagonists have shown to blunt this morning peak. However, previous reports studying the effects of beta blockers on the circadian variation did not analyze the underlying cause of sudden cardiac death. It thus remains unclear whether ventricular tachyarrhythmias are influenced by beta-blocker therapy.

HYPOTHESIS

This study tested the hypothesis that beta-blocking agents blunt the morning peak of life-threatening ventricular tachyarrhythmias.

METHODS

In 87 patients who were treated and monitored with an implantable cardioverter defibrillator, the circadian distribution of ventricular tachyarrhythmias terminated by appropriate shocks was analyzed and compared in those receiving beta blockers versus those not receiving beta-blocker therapy.

RESULTS

Tachyarrhythmic episodes in the absence of beta-blocker therapy (n = 344) exhibited a circadian variation with a distinct morning peak (16, 38, 28, and 18% of episodes at 0-6, 6-12, 12-18, and 18-24 h, respectively, p < 0.001). In contrast, tachyarrhythmic episodes during beta-blocker therapy (n = 104) were equally distributed over time (22, 27, 24, and 27% of episodes at 0-6, 6-12, 12-18, and 18-24 h, respectively, p = 0.95). The circadian distribution of episodes was significantly different in patients with and those without beta blockade (p < 0.05).

CONCLUSION

Beta-adrenergic antagonists influence the circadian distribution of malignant ventricular tachyarrhythmias in patients with an implantable cardioverter defibrillator. The blunted morning peak of tachyarrhythmic events during beta blockade supports the hypothesis that a sympathetic surge is involved in the circadian pattern of malignant arrhythmias.

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.