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.