Influence of climatic variables on acute myocardial infarction hospital admissions

https://doi.org/10.1016/j.ijcard.2008.06.036Get rights and content

Abstract

Background

Seasonal peaks in acute myocardial infarction (AMI) incidence have been widely reported. Weather has been postulated to be one of the elements at the basis of this association. The aim of our study was to determine the influence of seasonal variations and weather on AMI hospital admissions.

Methods

We correlated the daily number of AMI cases admitted to a western Sicily hospital over twelve years and weather conditions on a day-to-day basis. Information on temperature, humidity, wind force and direction, precipitation, sunny hours and atmospheric pressure was obtained from the local Birgi Air Force base. A total of 3918 consecutive patients were admitted with AMI over the period 1987–1998 (2822 men, 1096 women; M/F: 2,58).

Results and conclusions

A seasonal variation was found with a significant winter peak. The results of multivariate Poisson analysis show in both sexes a significant association as regards the incidence relative ratio between the daily number of AMI hospital admission and minimal daily temperature and maximal daily humidity. The incidence relative ratios (95% confidence intervals) were, in males, 0.95 (0.92–0.98) (p < 0.001) as regards minimal temperature and 0.97 (0.94–0.99) (p = 0.017) as regards maximal humidity. The corresponding values in females were respectively 0.91 (0.86–0.95) (p < 0.001) and 0.94 (0.90–0.98) (p = 0.009).

Environmental temperature, and also humidity, may play an important role in the pathogenesis of AMI. These data may help in understanding the mechanisms whereby AMI events are triggered and in organizing better the assistance to ischemic patients throughout the year.

Introduction

Seasonal peaks in diseases incidence and mortality with a winter increase in deaths have been reported in different countries [1], [2], [3]. This phenomenon has been attributed to seasonal variations in respiratory, cardiovascular, and cerebrovascular mortality [3]. In particular, numerous studies have reported increased coronary heart disease (CHD) mortality during the winter [4], [5], [6].

Consensus is lacking, however, on whether this phenomenon reflects variations in incidence or in case fatality rate. Variations in emergency admission rates and trial recruitment of patients suffering from acute myocardial infarction (AMI) [4], [7] are well described, and a number of epidemiological studies have reported a greater winter AMI incidence, with similar seasonal trends in all studied subgroups, including men and women, middle-aged and elderly patients, patients from northern and southern states and those with Q wave and non-Q wave AMI [9], [10], [11]. This relation, besides, could be actually U-shaped, with higher mortality also in extremely hot summer [12], [13].

These seasonal changes do not seem universal [14], [15] as they are absent near the equator or in subpolar regions with less temperature fluctuations unlike those found in temperate regions. For this reason it seems inadequate to extrapolate the results in other parts of the world to any particular environment. Up to now the effect of climatic variables on AMI has not been assessed in Sicily, a country with a mild climate. Finally, meteorological factors other than atmospheric temperature were less frequently studied. A better understanding of these seasonal patterns may provide novel avenues in cardiovascular disease prevention.

The aim of this study is to explore the short term association between some meteorological variables and AMI hospital admissions in a Mediterranean location, the city of Trapani, Italy.

Section snippets

Materials and methods

We retrospectively analysed the number of daily emergency AMI hospital admission in a single centre with an intensive Coronary Care Unit (CCU) during a twelve year period (1/1/1987–31/12/1998).

Results

A total of 3918 patients have been admitted with AMI diagnosis over the studied period (2822 men, 1096 women; male/female ratio: 2,58; mean age 67.3+/− 8.2; mean age in males 62.8+/− 7.9, mean age in female 71.6+/− 9.1).

The number of admissions along the different years in both sexes is shown in Fig. 1. Fig. 2 shows monthly distribution of hospital AMI admissions, both total and by single gender. The existence of a greater number of admissions in winter (most in February in males and in December

Discussion

Although considerable advances in identifying the conditions that may predispose to atherosclerosis have occurred [16], less information is known about the incident events leading to plaque rupture. The classical risk factors only partially account for the variations in AMI incidence. Therefore, also other so far unknown elements influence AMI rates, among which could be meteorological factors.

Our data, according to other studies [7], [8], [9], [10], [11], confirm the greater AMI incidence in

Limitations

There are some potential limitations to our study. First, morbidity studies based on hospital admissions explore only selected events in patients surviving long enough to be hospitalised, not allowing to report true AMI incidence. Second, in a study where computer databases are the only data source, the quality in terms of completeness and accuracy can limit the conclusions. Third, the recorded ecologic temperature of a specified geographic area may not accurately represent the actual

Conclusions

The excess of AMI admissions associated with a cold and humid environment is a significant public health problem. The present results have several potential implications regarding the pathophysiological mechanisms of AMI and its prevention. Several public health actions have been proposed to prevent the negative health effects of temperature, such as educational programmes to produce behavioural changes in the population (clothing, time spent outdoors, adequate diet) and social measures (home

Acknowledgements

We are grateful to the 37th Airbrigate's Meteorological Office of the Italian Air Force of Trapani Birgi, and to the National Centre of Air Meteorology and Climatology of the Italian Air Force of Pratica di Mare, which provided the meteorological data, as well as to Rossella Alduino and Antonella Sferrazza, who performed the statistical analysis.

The authors of this manuscript have certified that they comply with the Principles of Ethical Publishing in the International Journal of Cardiology [44]

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