CIRCADIAN DISTRIBUTION OF ONSET OF ACUTE MYOCARDIAL-INFARCTION IN SUBGROUPS FROM ANALYSIS OF 10,791 PATIENTS TREATED IN A SINGLE CENTER

A circadian variation of symptom onset in acute myocardial infarction (AMI) with an increased frequency in the late morning and possibly also in the evening has been found in several studies. It has been suggested that different circadian rhythms may exist in various subgroups of patients. This possibility was examined in a population of 10,791 patients collected between 1973 and 1987 in a continuously operating register of patients with AMI in Malmo, Sweden. In 6,763 patients (63%) in whom a distinct symptom onset could be established, symptom onset occurred with an increased frequency between 6:01 A.M. and 12:00 noon (30.6%) and between 6:01 P.M. and 12:00 midnight (26.9%). Similar bimodal circadian rhythms were seen in patients aged > 70 years (n = 2,923), less-than-or-equal-to 70 years (n = 3,840), men (n = 4,528), women (n = 2,235), smokers (n = 2,458), hypertensives (n = 1,999), diabetics (n = 653), patients with (n = 1,872) and without (n = 4,891) a history of previous AMI, and in patients with recent non-Q-wave AMI (n = 333). In 455 patients receiving cardioselective beta-blockers the circadian distribution did not differ from a random, whereas in patients taking nonselective beta-blockers or calcium antagonists significant bimodal rhythms were found. Statistically significant interactions were found between symptom onset and age dichotomized at 70 years, and between patients with and without a history of previous AMI. In a multivariate analysis only these variables (age less-than-or-equal-to/> 70 years; +/- history of a previous AMI) were found to modify the circadian rhythm of symptom onset in the population. It is suggested that only minor differences in symptom onset between various subgroups exist within the same population, and that these differences probably are unable to explain differences in circadian rhythm of symptom onset between different populations.