Interaction of septadian and circadian rhythms in life-threatening ventricular arrhythmias in patients with implantable cardioverter-defibrillators

Previous studies have shown that life-threatening ventricular arrhythmias d isplay both circadian and septadian (day of the week) periodicity. We hypot hesized that assessing the relation between these circadian and septadian r hythms may provide important pathophysiologic information about the mechani sm of sudden cardiac death. Using the database from a population of 683 con secutive patients with a third-generation implantable cardioverter-defibril lator (ICD), we examined the time pattern of ICD activations for rapid (pro spectively defined as cycle length <280 ms) tachycardias for each day of th e week. A total of 5,270 arrhythmic episodes were analyzed. Despite the fac t that event distribution was significantly nonuniform (p <0.001) for both circadian and septadian analyses, the circadian pattern was strikingly simi lar for each day df the week with a relatively broad peak between 9 A.M. an d 6 P.M, and a long nadir between 9 P.M, and 6 A.M. We conclude that the tr igger factors responsible for the daily circadian distribution of life-thre atening ventricular arrhythmias in a population with ICDs are similar throu ghout the week and may thus be unrelated to the standard work week. These d ata suggest that the physiologic modulators of circadian and septadian rhyt hms may be different. (C) 1999 by Excerpta Medico, Inc.