CIRCADIAN, DAY-OF-WEEK, AND SEASONAL VARIABILITY IN MYOCARDIAL-INFARCTION - COMPARISON BETWEEN WORKING AND RETIRED PATIENTS

The circadian, day-of-week, and seasonal distributions of acute myocar dial infarction and its association with the patients' working status were analyzed in a regionally defined population (n = 103,322) monitor ed from 1980 to 1988. Included were 2906 consecutive patients (1746 [6 0.1%] men and 1160 [39.9%] women; mean age 67.8 years) with confirmed diagnosis (by standardized diagnostic criteria in hospitalized patient s and autopsy results in out-of-hospital deaths). The time of myocardi a( infarction on the basis of onset of symptoms was known in 1901 case s. Myocardial infarction occurred more frequently (p < 0.05) during th e morning from 7:00 to 10:00 AM, on Mondays, and during the winter fro m January to March compared with other times of day, days of the week, and seasons. Compared with retired patients, working patients (32%) h ad a second circadian peak, in the afternoon at 4:00 PM (P < 0.05), an d a trend toward an additional seasonal peak in September (p value not significant), whereas the day-of-week pattern was similar in the two subgroups. The occurrence of myocardial infarction demonstrates marked circadian, day-of-week, and seasonal variations, with some difference s between working and retired patients. Further investigation of possi ble triggering events may aid in identifying underlaying mechanisms an d perhaps in improving prevention of the disease.