PATHOPHYSIOLOGY AND NATURAL HISTORY SUDDEN DEATH Circadian variation in the frequency of sudden cardiac death

To determine whether sudden cardiac death exhibits a circadian rhythm similar to that recently demonstrated for nonfatal myocardial infarction, we analyzed the time of day of sudden cardiac death as indicated by death certificates of 2203 individuals dying out of the hospital in Massachusetts in 1983. The data reveal a prominent circadian variation of sudden cardiac death, with a low incidence during the night and an increased incidence from 7 to 11 A.M. The pattern is remarkably similar to that reported for nonfatal myocardial infarction and episodes of myocardial ischemia. The finding that the frequency of sudden cardiac death is increased in the morning is compatible with hypotheses that sudden cardiac death results from ischemia or from a primary arrhythmic event. Further study of the physiologic changes occurring in the morning may provide new information supporting or refuting these hypotheses, thereby leading to increased understanding and possible prevention of sudden cardiac death. Circulation 75, No. 1, 131-138, 1987. ALTHOUGH sudden cardiac death afflicts over 400,000 individuals each year in the United States alone and accounts for approximately 50% of all deaths from coronary artery disease,l1 the mechanisms triggering this common catastrophic event remain obscure. Attempts to identify precipitating mechanisms have been hampered by the rarity of intensive medical observation in the critical moments before its onset. Although frequent in a population, sudden cardiac death is difficult to study because it is impossible to predict in which individual it will occur, and it often occurs without warning in an out-of-hospital setting. Retrieval of physiologic data from those who die is impossible, while in those who are resuscitated, the period of arrest and the techniques of resuscitation obscure the events that preceded the arrest. Of necessity, therefore, our present, limited insight into the mechanism of sudden cardiac death is based primarily on knowledge, gained from extensive epidemiologic and pathologic studies, of predisposing factors. Such studies indicate that sudden cardiac death frequently occurs in individuals younger than 65 years of age with no prior overt signs of cardiac disease,2 4 and From the Cardiovascular Division, Brigham and Women's Hospital, Harvard Medical School, Boston. Address for correspondence: James E. Muller, M.D., Harvard Medical School, 164 Longwood Ave., Boston, MA 02115. Received July 1, 1986; revision accepted Sept. 18, 1986. Vol. 75, No. 1, January 1987 is most likely to afflict those demonstrating the traditional risk factors for ischemic heart disease.4' 5 Pathologic studies have confirmed that sudden cardiac death generally occurs in individuals with extensive coronary atherosclerosis and myocardial damage.36 Holter monitoring has demonstrated that ventricular tachycardia degenerating to ventricular fibrillation is often the final event leading to sudden cardiac death,7 but the subset of patients undergoing Holter monitoring may not be representative of the larger group experiencing sudden cardiac death, and the mechanisms precipitating the fatal arrhythmia have not been identified.8 A new approach to identification of the mechanisms precipitating sudden cardiac death is suggested by the recent demonstration that nonfatal myocardial infarction, an event that is closely associated with sudden cardiac death and shares its unexpected onset, is more likely to occur in the morning than at other times of day.9 In addition, episodes of angina at rest,10 silent myocardial ischemia,"1 and the onset of stroke'2 have all been reported to have similar circadian rhythms. We therefore examined the time of day of sudden cardiac death in 2203 individuals dying in Massachusetts in 1983. The data reveal a circadian rhythm of sudden cardiac death remarkably similar to that observed for nonfatal myocardial infarction, episodes of myocardial ischemia, and stroke. Further characterization of the time of occurrence of sudden cardiac death, 131 by gest on A ril 2, 2017 http://ciajournals.org/ D ow nladed from