Circadian, day-of-week, and age patterns of the occurrence of acute coronary syndrome in Beijing's emergency medical services system

BACKGROUND: Previous in-hospital studies suggest that there are significant circadian rhythms associated with the incidence of acute coronary syndromes (ACSs). No study to date has examined the presentation of ACS in the prehospital setting. Our goal was to examine circadian, day-of-week, and age patterns of occurrence in ACS in a large, urban emergency medical services (EMS) system. METHODS: We retrospectively reviewed the electronic prehospital medical records from the Beijing's EMS system spanning August 1, 2005, to July 31, 2007. Data were analyzed by hour of the day and day of the week. χ(2) tests were performed to compare the difference. RESULTS: Seven thousand thirty-two cases of ACS were identified by the EMS system physicians during the 2-year study period, including 536 cases of acute myocardial infarction. A significant variation of circadian distribution of ACS was observed in both 24-hour (P < .001) and 2-hour (P < .001) interval time course. Two peaks were observed in the morning from 0800 to 1000 and approaching midnight from 2200 to 2400. Increases of 50% and 60.8% in the morning and evening peaks were found, respectively, when compared with the early morning baseline (nadir). No significant difference was found among the accumulated cases in 2 years on each day in a week (P = .203). CONCLUSIONS: Our study shows that, in the Beijing metropolitan area, the presentation of ACS has significant circadian rhythm characterized by 2 peaks within 24 hours, the morning peak is 0800 to 1000, and the late evening peak is 2200 to 2400. No significant weekly rhythm was observed in the present study.