Circadian variation in the onset of acute myocardial infarction: lack of an effect due to age and sex.

The circadian patterns in the onset of symptoms of acute myocardial infarction were assessed in a prospective study involving 450 patients. Analysis of the data in the 424 patients in whom the time of onset was known did not show any statistically significant circadian rhythms, either for the group as a whole or for subgroups divided according to sex, age group (< 60, 60-69, 70-79 and > or = 80 years old), or the presence or absence of diabetes mellitus. The frequency of onset of symptoms was highest in the morning (06.01-12.00 h) for the group as a whole (29.2%). Patients aged < 70 and > or = 80 years old showed a peak in the morning, whereas patients aged 70-79 years old showed a peak in the afternoon (12.01-18.00 h).