Influence of weather conditions on the frequent onset of acute myocardial infarction.

BACKGROUND: This study was conducted to clarify the influence of weather conditions on the onset of acute myocardial infarction (AMI) in Kumamoto. METHODS: We studied 642 consecutive patients (males 433, females 209; 71±13 years) who were admitted with AMI. Days of frequent onset (F-days) were defined as days on which ≥2 patients had been admitted for AMI, whereas days of non-frequent onset (N-days) indicated those with fewer than 2 admissions for AMI. Meteorological factors, including the mean atmospheric pressure and rainfall, the mean, maximum, and minimum temperature, intra-day temperature difference, humidity, wind speed, and the number of sunlight hours, were analyzed. All variables were measured on the day of onset of AMI and on each of the 2 days immediately prior to the day of onset. RESULTS: There were 86 F-days and 1740 N-days. F-days were significantly associated with lower air temperature (mean, maximum, and minimum), higher intra-day temperature difference, lower humidity, and longer daily duration of sunlight compared with N-days. In addition, meteorological factors for frequent onset of AMI affected older subjects to a greater extent than either young or female subjects. Multiple logistic regression analysis showed that minimum temperature two days before onset was associated with the frequent onset of AMI (odds ratio, 0.805; p<0.05). CONCLUSION: Lower minimum temperature on the 2nd day preceding the onset is an independent risk factor for the frequent onset of AMI. The association between low ambient temperature and frequent onset of AMI was stronger in elderly and female subjects.