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If your emergency department (ED) has been seeing a lot of heart attacks recently, you might blame weather events. Consider the ups and downs in March, when four nor’easters in three weeks brought frigid weather interspersed with spring-like temperatures.
Research presented at the American College of Cardiology’s 67th Annual Scientific Session in Orlando, FL, suggests that dramatic day-to-day swings in temperature led to more cardiac events. The concern is that if climate change creates more weather variation, then heart attacks might increase.
“Global warming is expected to cause extreme weather events, which may, in turn, result in large day-to-day fluctuations in temperature,” lead author Hedvig Andersson, MD, a cardiology researcher at the University of Michigan, suggested in a university press release. “Our study suggests that such fluctuations in outdoor temperature could potentially lead to an increased number of heart attacks and affect global cardiac health in the future.”
Although past research has linked myocardial infarction to environmental stress, few studies have looked at the influence of outdoor temperature. To better understand the connections, the study team identified patients presenting with ST-elevation myocardial infarction (STEMI) who were treated with primary percutaneous coronary intervention in Michigan from 2010 to 2016.
At the same time, the researchers collected daily minimum, maximum, and average temperatures on hospital ZIP code level. Absolute temperature change (ΔT) was defined as the maximum difference in temperature on the day of STEMI presentation and the day before.
Included were 30,404 patients presenting with STEMI at 45 hospitals across the state. Results demonstrated about a 5% increased risk of a heart attack for every five-degree jump in temperature differential in degrees Celsius, which is about nine degrees Fahrenheit. More dramatic swings — exceeding 25 degrees Celsius (45 degrees Fahrenheit) — were linked to a greater increase in heart attack rates vs. a smaller increase with temperature swings of 10 to 25 degrees Celsius (18 to 45 degrees Fahrenheit). The effect was intensified when the high temperature for the day was warmer.
As an example, on a very warm day, nearly twice as many heart attacks were predicted with a temperature fluctuation of 35 to 40 degrees Celsius (63 to 72 degrees Fahrenheit) than on days without those temperature extremes, the researchers point out.
“Generally, we think of heart attack risk factors as those that apply to individual patients, and we have, consequently, identified lifestyle changes or medications to modify them. Population-level risk factors need a similar approach,” notes senior author Hitinder Gurm, MD, professor of medicine and associate chief clinical officer at Michigan Medicine. “Temperature fluctuations are common and [often] predictable. More research is needed to better understand the underlying mechanisms for how temperature fluctuations increase the risk of heart attacks, which would allow us to perhaps devise a successful prevention approach.”
Andersson said the underlying mechanism behind the effect is unknown but suggests, “While the body has effective systems for responding to changes in temperature, it might be that more rapid and extreme fluctuations create more stress on those systems, which could contribute to health problems.”
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