Objectives: The association between the occurrence of acute myocardial infarction and meteorological factors was examined in five cities of the Chugoku area in Japan.
Methods: This study used the emergency admission data for acute myocardial infarction in Yamaguchi, Matsue, Tottori, Okayama (from April 2000 to March 2005), and Hiroshima (from January 1993 to December 2002). Daily meteorological data was obtained from The Japan Meteorological Agency. The Poisson regression model was used to examine the association between acute myocardial infarction and daily average temperature and pressure.
Results: In Hiroshima, Okayama, Yamaguchi and Matsue City, daily average events of acute myocardial infarction were 30%, 30%, 33% and 40% higher in winter than those in summer (p < 0.05). Daily average events increased as atmospheric temperature decreased. In Hiroshima, Okayama and Yamaguchi City, daily average events in the low temperature group (T < 10 degrees C) were significantly higher than those in the high temperature group (T > or =20 degrees C) (p < 0.05). In Hiroshima City, a significant interaction was found between temperature and pressure. Daily events in the low temperature and low pressure group (1.38/day) was significant and 37% larger than in the high temperature and moderate pressure group (0.94/day; risk ratio = 1.37, 95% confidence interval 1.01-1.86, p < 0.05). Days with low temperature and low pressure were characterized by rain and/or snow.
Conclusions: The occurrence of acute myocardial infarction was associated with low temperatures, especially daily average temperature lower than 10 degrees C. The risk was high on days with low temperature and low pressure in Hiroshima City.