Circadian variation of the onset of acute myocardial infarction in the Osaka area, 1998-1999 - Characterization of morning and nighttime peaks

The onset of acute myocardial infarction (AMI) shows characteristic circadi an variations; that is, a definite morning peak related to biologic rhythms and a vague nighttime peak related to socioeconomic factors. The recent ec onomic recession in Japan may change the circadian variation, especially th e nighttime peak. This study evaluated the recent circadian variation of AM I in Osaka and specified the patient subgroups showing either a morning or nighttime peak predominantly. Of 1,609 consecutive patients with AMI regist ered from April 1998 to January 2000, 1,252 whose onset of AMI was definite ly identified were studied. The day was divided into six 4-h periods with a morning peak between 08.01h and 12.00h, and nighttime peak between 20.01h and 24.00h. When subgroup analysis was performed, female patients aged 65 y ears or more showed a morning peak alone and male patients aged less than 6 5 years with an occupation and the habits of cigarette smoking and alcohol intake showed a nighttime peak alone. Thus, in Osaka nighttime socioeconomi c factors may currently be more potent triggers of AMI than the morning sur ges in younger male workers who smoke and drink.