MODIFICATION OF THE CIRCADIAN PATTERN OF VENTRICULAR TACHYARRHYTHMIASBY BETA-BLOCKER THERAPY

Background: Sudden cardiac death exhibits a circadian variation and pr edominantly occurs during morning hours. Beta-adrenergic antagonists h ave shown to blunt this morning peak. However, previous reports studyi ng the effects of beta blockers on the circadian variation did not ana lyze the underlying cause of sudden cardiac death. It thus remains unc lear whether ventricular tachyarrhythmias are influenced by beta-block er therapy. Hypothesis: This study tested the hypothesis that beta-blo cking agents blunt the morning peak of life-threatening ventricular ta chyarrhythmias. Methods: In 87 patients who were treated and monitored with an implantable cardioverter defibrillator, the circadian distrib ution of ventricular tachyarrhythmias terminated by appropriate shocks was analyzed and compared in those receiving beta blockers versus tho se not receiving beta-blocker therapy. Results: Tachyarrhythmic episod es in the absence of beta-blocker therapy (n = 344) exhibited a circad ian variation with a distinct morning peak (16, 38, 28, and 18% of epi sodes at 0-6, 6-12, 12-18, and 18-24 h, respectively, p<0.001). In con trast, 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 ventric ular tachyarrhythmias in patients with an implantable cardioverter def ibrillator. The blunted morning peak of tachyarrhythmic events during beta blockade supports the hypothesis that a sympathetic surge is invo lved in the circadian pattern of malignant arrhythmias.