LONDON – For every 10° C drop in the highest daily air temperature, the risk for ST-elevation myocardial infraction was found to increase by 7% in a Canadian study.
Researchers at the University of Manitoba in Winnipeg performed a retrospective study of all STEMI cases that had occurred in the city during 2009-2014 and linked them to daily air temperatures collected from Environment Canada.
Dr. Shuangbo Liu
“There is a clear correlation between cold weather and heart attacks,” said Dr. Shuangbo Liu, who presented the findings at the annual congress of the European Society of Cardiology. Previous studies have shown that the incidence of, hospitalization for, and death as a result of, MI are all increased as the weather gets colder. But until now, it wasn’t known what the specific relationship between temperature drops and the rate of STEMI was, she explained.
STEMIs typically occur as a result of acute rupture of an atherosclerotic plaque, but although the risk factors for the development for the plaques have been widely studied, the risk factors for rupture are not so well defined. There is some suggestion that colder weather is linked to factors that might predispose to plaque rupture, such as an increased cardiac workload, higher blood pressure, and an increased procoagulant state.
Winnipeg is one of the coldest large cities in the world in winter, but has more temperate fall and spring seasons with hot and dry summers, and so provided the ideal place to study the effect of environmental temperature on the risk of STEMI, Dr. Liu said.
Over the 6-year retrospective audit period, 1,817 STEMIs were recorded. Only STEMIs that were reported within 12 hours of admission were included in the analyses, with almost all (95%) patients undergoing primary percutaneous coronary intervention.
The highest daily temperature reached was 20° C on 31% of the study days, 0°-20° on 38% of the study days, and less than 0° on 32% of the study days.
The cold – but not warm – weather was associated with the risk of STEMI, with the daily high temperature being the strongest predictor of having a heart attack. On the study days where the highest temperature reached was less than 0°, the STEMI event rate was 0.94 per day. This rate was significantly higher than that when the daily high temperature was above 0°, at a rate of 0.79 per day overall (P less than .001)
STEMI rates on days that were 0°-10°, 10°-20°, 20°-30°, and 30° and above were 0.89, 0.81, 0.74, and 0.61 per day, respectively.
Although any snowfall in the last 2 days was predictive of STEMI on univariate analysis, upping the risk by 20%, it did not remain so after adjustment for temperature.
The daily high temperatures on the 1-2 days preceding STEMI were found to be predictive in univariate analyses, increasing the relative risk by 19%-20% (P less than .001).
Dr. Liu acknowledged the limitations of using retrospective administrative data and that further prospective validation of the results would be needed. However, these data are “thought provoking,” she said, and suggest that increasing public awareness is needed and perhaps health care resources need to be reallocated to help prevent the seasonal surge in STEMI observed in the study.
Dr. Liu reported having no relevant financial disclosures.