Circadian occurrence of symptomatic paroxysmal supraventricular tachycardia in untreated patients.

Fifty-two patients with paroxysmal supraventricular tachycardia were studied to determine whether there was a circadian pattern to the occurrence of this arrhythmia. Antiarrhythmic therapy was discontinued, and patients were followed until they had one recurrence of tachycardia documented by telephone transmission of the electrocardiogram. By least-squares analysis, the times of day that the 52 attacks (one from each patient) occurred were fit to a sinusoidal density function with a period of 24 hr. The highest relative incidence of tachycardia was at 4 P.M.; tachycardia was five times more likely to occur at 4 P.M. than at 4 A.M., the time of the lowest relative incidence. A second attack of tachycardia was recorded from 35 of the 52 patients. The times of the two attacks in individual patients were found to be independent; thus the times of day at which the second attacks occurred were used as a test set for the distribution estimated from the first. The empirical distribution for the times from the 35 second attacks was compared with the distribution function estimated from the 52 first attacks, and there was no significant departure; this finding confirmed the circadian pattern. Since the relative incidence of attacks of paroxysmal supraventricular tachycardia is higher in the afternoon, it may be helpful to target antiarrhythmic therapy to that time of day.