Circadian rhythm in sudden cardiac death: a retrospective study of 2,665 cases.

Several studies have reported a circadian variation in sudden cardiac death. The aim of this study was to determine whether in northern Greece sudden cardiac death shows a circadian rhythm and/or a weekly and seasonal distribution. We studied 2,665 sudden deaths due to coronary heart disease from 13,832 sudden deaths that merited autopsy; 1,429 (53.6%) of them were due to acute myocardial infarction (AMI) and 1,236 (46.4%) to chronic ischemic heart disease (IHD). The time of death was determined on the basis of autopsy results and witness interviews. There was a circadian rhythm of sudden cardiac death (p<0.010), with a low incidence during the hours 04.00-08.00 (13.1%) and an increased incidence during 20.00-24.00 (19.8%) (p<0.05). Women did not show the same significant circadian variation. Time of occurrence of sudden cardiac death attributed either to AMI or to IHD showed a similar 24-hour distribution (lowest incidence during 04.00-08.00 hours, 12.8% and 13.5%, respectively, and higher during 20.00-24.00, 19.5% and 20.3%, respectively). Weekday distribution of sudden cardiac death showed a significant statistical variation (p<0.005) with the highest frequency on Monday (21.1%) and the lowest on Sunday (7.5%). The same distribution was observed in men, whereas in women the lower frequency was also on Sunday but the higher was on Tuesday. Sudden cardiac death was evenly distributed over the months of the year, with the highest incidence in summer (27.3%) and the lowest in autumn (22%). Sudden cardiac death shows a circadian rhythm and a significant variation during the week.