The effect of climate on heart attack mortality

Abstract

We have read with great interest the very important letter by George Ntaios et al. about whether there is a geographic variation in the seasonal distribution of acute myocardial infarction and sudden cardiac death [1]. The authors believe that a possible factor causing the differences between Hungarian and Greek results could be that Greece is amajor touristic target, resulting in a large increase of population during the summer.We also consider to analyze the seasonal composition of the population, to determine the extent of contribution of data deriving from cases of nonresident aliens in our results. Another factor causing this deviation between the results of the two countries could be the difference in climate. The climate of Greece is as diverse as its geographical construction. It is also important to note that our study included all patients died following acute myocardial infarction not only cases classified as sudden cardiac deaths. And while the Greek study focused on deaths occurred in the Municipality of Thessaloniki, northern Greece, the Hungarian study covered the whole territory of the country. Several reports have already proved that the number of deaths related to acute myocardial infarction (AMI) shows a seasonal variation, with a peak in winter, and a lowest number of mortality rates during the months of summer [2–4]. The effects of meteorological variables on the human organism have been studied for more than fifty years, and changes in the number of AMI events have been related to both cold or warm temperatures [5–7]. Hungary is a small country in the middle of Europe, laying in the Carpathian basin. Based on our results it may be stated that the annual number of cardiac mortality (N=16.160) in Hungary shows a steadily decreasing tendency between 2000 and 2005, with a seasonal variation regardless of age or sex. The peak period of AMI mortality was during the months of spring, with a lowest value during the summer. There was a significant difference between seasons (F=3.027; pb0.05). The daily average of cardiovascular mortality during each season was the following: 8.48 during spring, 7.23 during the summer, 7.79 during autumn, and 7.76 during winter. The low rate ofAMImortality during themonths of summermay be due to summer holidays in addition to favourable meteorological conditions, nutrition, exercise, or the more wide-spread use of air-conditioners. In addition to these findings, it seems that the changes of weather conditions also influence the mortality of other cardiovascular events. In Hungary the highest average daily temperature is above 29 °C in themonth of July, while the lowest average daily temperature is above 10 °C in December. With consideration to meteorological conditions, our results show, that both the sharp temperature increase during spring, and the similarly significant decrease of temperatures during autumn, both have an increasing effect on heart attack related mortality. Studying the moving average of AMI mortality (k=7), and the relation with the daily average temperature of the preceding 7 days, we have found a medium value negative correlation (r≅−0.466, pb0.001). Categorizing our data according to age groups, the strongest correlation was found in the age group of above 70 (r≅−0.41, pb0.001), with a weaker relation in the age group between 50 and 70 (r≅−0.315, pb0.001), while in the age group below 50 years of age, no correlation was found. Considering the International Journal of Cardiology 139 (2010) 92–104 www.elsevier.com/locate/ijcard