Effect of a long acting beta-adrenoceptor blocker on diurnal variation of cardiac dysrhythmias

Daily variations in the occurrence of symptomatic supraventricular tachycardia as determined by ambulatory event monitoring

The diurnal incidence of supraventricular tachycardia (SVT), including atrial fibrillation and atrial flutter, has been quantified by examining 7,891 cases of symptomatic arrhythmia in 5,869 patients assigned to ambulatory monitoring using electrocardiographic event recorders with transtelephonic reporting. The probability of occurrence of SVT was found to be high and moderately variable throughout the normally active hours of the day between 8 A.M. and 8 P.M. and to be uniformly low during the inactive hours between 1 and 5 A.M. Age-related peaks within the active phase were independently associated with the older half of the study population (9 A.M.) and with the younger half (6 P.M.). The daily incidence of SVT is primarily characterized by 2 states of activity, active and quiescent. Quiescence of SVT is associated with normal sleep and inactivity.

Double-peaking circadian variation in the occurrence of sustained supraventricular tachyarrhythmias

We studied 251 patients less than or equal to 65 years of age admitted for treatment of symptomatic supraventricular tachyarrhythmia to assess whether these arrhythmias begin evenly throughout the day or manifest circadian variation in occurrence. The arrhythmias included 152 episodes of atrial fibrillation, 50 episodes of supraventricular reentry tachycardia, 30 episodes of atrial flutter, and 19 cases of ectopic atrial tachycardia. A total of 209 patients could tell the exact time their symptoms had started. In 38 of them (18%), the arrhythmia had begun between midnight and 6:00 AM, in 63 (30%) between 6:01 AM and noon, in 46 (22%) between noon and 6:00 PM, and in 62 (30%) between 6:01 PM and midnight. This distribution differed significantly from uniform occurrence (chi square 8.7, p less than 0.05). Fifty patients were using beta-adrenoceptor blocking agents when the arrhythmia occurred. Compared with the other 159 patients, they had no morning surge of arrhythmias (20% versus 33.3% of episodes between 6:01 AM and noon), but instead a much higher incidence at night (34% versus 13.2% of episodes between midnight and 6:00 AM) (chi square 14.4, p less than 0.005). We conclude that the frequency of onset of sustained supraventricular tachyarrhythmias varies with the time of day, showing nearly equal peaks in the morning and in the evening and a trough at night. The modifying effect of beta-adrenoceptor blockage suggests that many morning arrhythmias are of adrenergic origin while other, probably vagal arrhythmogenic mechanisms, prevail at night.

Circadian variation in ventricular electrical instability associated with coronary artery disease

Although sudden cardiac deaths and ischemic cardiac events clearly occur in a circadian pattern, such a pattern has not been shown for primary arrhythmic events. Because primary arrhythmic events are thought to play an important role in sudden cardiac death, a large series of ventricular stimulation studies was analyzed to determine whether circadian variation in ventricular electrical instability exists. If such a circadian variation could be shown, it could have implications for the conduct and interpretation of electrophysiologic testing and the etiology of circadian variation in sudden cardiac death. Results of 2 drug-free ventricular stimulation studies performed 4 to 28 hours apart in each of 162 patients with coronary artery disease were analyzed. Rate and duration of induced arrhythmia, number of extrastimuli required to induce arrhythmia and changes in these factors between the 2 tests in each patient were analyzed. Comparisons were made by half-day, by hour and in a temporally continuous manner to eliminate errors associated with any single method. No significant circadian variation was found in any electrophysiologic measure of ventricular electrical instability despite adequate statistical power. These findings show that the time of day during which ventricular stimulation tests are performed does not affect test results, and therefore does not need to be controlled during electrophysiologic studies. If these findings are parallel to those in ambulatory patients with coronary artery disease, then circadian changes in ventricular electrical instability may not play as important a role in the circadian pattern of sudden cardiac death as had been previously thought.