Contents of second peak in the circadian variation of acute myocardial infarction in the Japanese population

Background: Circadian variation has been accepted as a factor in acute myocardial infarction (AMI). An increased incidence of cardiac events in the morning has been reported for a long time. Recent reports have indicated that the onset of AMI shows two peaks, which occur in the morning and evening. It has also been demonstrated that circadian pattern of AMI may vary with sex and age. Methods and results: We investigated 522 consecutive patients who underwent primary percutaneous coronary intervention (PCI) for ST segment elevation myocardial infarction (STEMI) between 2000 and 2010. The patients were classified into 3 age groups: younger (<= 59 years old), intermediate (60-79 years old), and older (>= 80 years old). Clinical data were investigated, including the age and sex, angiographic characteristics, and time of onset of STEMI. There were two peaks in the onset of STEMI throughout the day, which were at 7:00-10:00 and 19:00-21:00 h, among all patients (male and female). Stratified analysis showed that older females formed the main part of the second peak. Conclusions: There were two peaks in the onset of STEMI in a Japanese population in Tokyo. The second peak was significantly dominated by the older female group. Age and gender influenced the second peak in the circadian variation of AMI in a Japanese population in Tokyo. (C) 2011 Japanese College of Cardiology. Published by Elsevier Ltd. All rights reserved.