Seasonality and daily weather conditions in relation to myocardial infarction and sudden cardiac death in Olmsted County, Minnesota, 1979 to 2002.

OBJECTIVES We assessed the relationship of season and weather types with myocardial infarction (MI) and sudden cardiac death (SCD) in a geographically defined population, and tested the hypothesis that the increased risk in winter was related to weather. BACKGROUND Winter peaks in coronary heart disease (CHD) have been documented. Yet, it is uncertain if seasonality exists for both incident events and deaths, and the role of weather conditions is not clear. METHODS The daily occurrence of incident MI and SCD in Olmsted County was examined with data from the National Weather Service. Poisson regression models were used to assess the relative risks (RRs) associated with season and climatic variables. Subsequent analysis stratified SCD into those with and without antecedent CHD (unexpected SCD). RESULTS Between 1979 and 2002, 2,676 MI and 2,066 SCD occurred. The age-, gender-, and year-adjusted RR of SCD, but not of MI, was increased in winter versus summer (1.17, 95% confidence interval [CI] 1.03 to 1.32) and in low temperatures (1.20, 95% CI 1.07 to 1.35, for temperatures below 0 degrees C vs. 18 degrees C to 30 degrees C). These associations were stronger for unexpected SCD than for SCD with prior CHD (p < 0.05). After adjustment for all climatic variables, low temperature was associated with a large increase in the risk of unexpected SCD (RR = 1.38, 95% CI 1.10 to 1.73), while the association with winter declined (RR = 1.06, 95% CI 0.83 to 1.35). CONCLUSIONS These data suggest that the winter peak in SCD can be accounted for by daily weather.