Variations in the incidence of acute myocardial infarction (AMI) during the day and week may differ among the subpopulations within the communities. It is well known that AMI onset shows characteristic circadian variations involving a definite morning peak and a vague nighttime peak: the former is often explained by biologic rhythms, while the latter by socioeconomic factors. Interestingly, we previously found that female patients aged 65 years or more showed a morning peak alone, whereas and male patients aged less than 65 years with an occupation and the habits of cigarette smoking and alcohol intake showed a nighttime peak alone. On the other hand, it is also reported that working population shows a weekly variation with an increased incidence for the AMI onset on Mondays. Accordingly, circadian variation for the onset of AMI could be influenced by each or combination of working status, gender, and the day of the week. However, there are few reports investigating circadian variation of AMI onset in relation with working status, gender and/or weekly variation. Therefore, we sought to investigate circadian variation patterns of AMI onset in relation with week variation according to gender and/or working status, especially in the working populations. From the registry database of the Osaka Acute Coronary Insufficiency Study (OACIS), a prospective observational study of AMI in Osaka area, Japan, a total of 7755 consecutive patients whose time of AMI onset was definitely identified between 1998 and 2009 were enrolled. The mean age of study population was 66+12 years old, 5872 (76%) were male, and 3364 (48%) had occupation. As previously reported, an increased incidence of AMI onset was observed in the morning and at the nighttime in overall populations. Interestingly, however, subgroup analysis revealed that the nighttime peak was completely attributable to the increase of nighttime onset on the weekend in the working subjects, especially working men, whereas the morning peak was common throughout the week with a peak on Monday in all other subgroups. As the weekend nighttime peak for AMI onset was not evident in other subgroups, this phenomenon may account for the social and/or economic reasons on the weekend in the working population. Although confirmation in other cohorts is required, this finding may help identify triggers of AMI and guide subjects to prevent an onset of AMI.
Circadian Variation of the Onset of Acute Myocardial Infarction in the Osaka Area, 1998-1999
