[An analysis of the circadian frequency in the onset of acute myocardial infarct].

The purpose of this study was to evaluate if the occurrence of acute myocardial infarction (AMI) follows a regular pattern during the day and, if so, to assess any difference according to sex and patients' age. To determine 24-hour trend of AMI onset, clinical recordings of patients admitted to the CCU for AMI over a period of 8 years were reviewed: 427 patients (310 men and 117 women, aged 24-95 years), with a first AMI and in whom the time of onset of cardiac pain due to MI could be accurately established by history, were selected. Analysis of hourly distribution of the event was performed using a mathematical model based on Whittaker's method for periodic phenomena. It showed the occurrence is cyclic with 2 waves with periods of 6 and 12 hours in all age groups in men an women. No statistical differences were found between observed figures of periods and values calculated by Fourier analysis. The overall occurrence of MI showed a regular pattern with 4 peaks at 4.00 am, 10.00 am, 4.00 am and 10.00 pm. This periodic behaviour is nearly the same both in men and in women. The occurrence of MI is maximal in the morning (34.2% in men, and 35.9% in women); the minimum was recorded during the evening in male patients over 70 years and during the night in the other age groups; it was recorded during the afternoon and the night in women.(ABSTRACT TRUNCATED AT 250 WORDS)