Background: To evaluate the relationship between site of infarction (anterior vs. inferior) and circadian variation in patients with ST segment elevation myocardial infarction (STEMI) in a Turkish cohort.
Material/Methods: This restrospective study enrolled 465 patients (407 male, mean age 65±7 years) with STEMI. Patients were then categorised into 4 6-hour increments according to the time of day during which the symptoms began (12:00 AM–06:00 AM, 06:00 AM–12:00 PM; 12:00 PM–06:00 PM and 06:00 PM–12:00 AM hours). Characteristics of patients by site of infarction (anterior vs. inferior) were compared.
Results: The frequency of onset of acute anterior MI as determined by onset of pain demonstrated significant circadian variation among the 4 time periods, demonstrating bimodal peaks (afternoon and morning) and a trough between 06:00 PM to 06:00 AM. The incidence of occurrence of MI between 06:00 AM to 06:00 PM was 4.50 times that of the average frequency of the remaining 12 hours of the day. The frequency of onset of acute inferior MI as determined by onset of pain exhibited significant circadian variation among the 4 time periods, demonstrating bimodal peaks (midnight to 06:00 AM and 06:00 AM to noon) and a trough between noon to midnight. The incidence of occurrence of MI between midnight to noon was 4.25 times that of the average frequency of the remaining 12 hours of the day.
Conclusions: Different circadian periodicity in the time of onset of STEMI was found regarding infarction site in a Turkish cohort. This may be related to genetic and⁄or demographic characteristics of the Turkish population.

Keywords: Myocardial Infarction - ultrasonography, Demography, Cohort Studies, Circadian Rhythm - physiology, Angiography, Time Factors, Turkey