Outdoor Temperature Swings Tied to STEMI Uptick

Marlene Busko

March 09, 2018

ORLANDO — More patients arrived at the hospital with an ST-segment-elevation myocardial infarction (STEMI) on days when the temperature fluctuated by more than 10 degrees Celsius, or more than 18 degrees Fahrenheit, early research suggests.  

Moreover, in this observational study of patients in Michigan, the effect was more noticeable on hot days, Hedvig Bille Andersson, MD, University of Michigan, Ann Arbor, and colleagues report.

"Daily temperature swings appear to be associated with increased risk of heart attacks, and the effect of these daily temperature swings is exaggerated on days that have a higher average temperature," study coauthor Hitinder S Gurm, MD University of Michigan, told the press during a briefing.

Andersson will present the study on March 10 at the American College of Cardiology (ACC) 2018 Scientific Session.

Global warming is expected to cause more instances of extreme weather, which could lead to an increased number of heart attacks, but climate change is also expected to decrease temperature fluctuation throughout the day, which would mitigate this effect, Andersson told theheart.org | Medscape Cardiology in an email.

In any case, "it is important to emphasize that the causal mechanism" behind this association between daily temperature variation and risk of STEMI remains unknown, he stressed.

More study is needed, Gurm said, "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."

In the meantime, since "we still know relatively little about the effect of external stress on the heart," Andersson said, echoing Gurm's remarks, "it remains important to focus on traditional cardiovascular risk factors, such as smoking and high blood pressure" to lower the risk for MI.

David A Alter, MD, University of Toronto, Ontario, Canada, who was not involved in this research, agreed that the "bottom line" is "such findings do need to be confirmed and reproduced in other studies."

"However, if true," he told theheart.org | Medscape Cardiology in an email, "the findings are not only provocative, but are meaningful in terms of how many people (ie, absolute number of patients) that could be at risk for STEMI in the population...from modest temperature fluctuations."

Temperature Shifts, Global Warming, and MI

"It's pretty well known that environmental stress can trigger myocardial infarctions, and people have had more myocardial infarctions when there are earthquakes, terrorist attacks, tsunamis," and other major stressors, including cold temperature, Gurm said, but it was not clear whether sudden temperature shifts were also a factor.

To investigate this, the researchers identified 30,404 patients who presented with STEMI and underwent primary PCI at 45 hospitals in Michigan from 2010 to 2016.

They examined the changes in temperature — adjusted for precipitation totals, day of the week, and seasonal trends — on the day of the STEMI.  

Compared with days with a steady temperature, defined as days where the difference between the minimum and maximum temperature was only 0 to 5 degrees Celsius, there was a 1.2% increase in the number of STEMI events on days when the temperature varied by 5 to 10 degrees Celsius.  

The number of STEMIs increased by 6.9% and by 11.1% on days when the temperature fluctuated by 10 to 15 degrees Celsius or by more than 15 degrees Celsius, respectively.

On the basis of these early findings, "I would be hesitant to label temperature fluctuations as a risk factor for MI," Alter cautioned. "Even if the findings were reproducible elsewhere, a risk factor implies causality. At this point, we only have an association or a 'signal.'" 

"That said, this study does add to an already large body of evidence that suggests that environmental factors are potentially important in determining the health (or lack thereof) of individuals," he said. "So, the findings are not entirely unexpected."

As far as "what effects, if any, global warming solutions may have on the risks of MI, this study only whets our appetite and justifies the need for more research, " Alter said.

Andersson has no relevant financial disclosures. Gurm has received fees/honoraria as a consultant for Osprey Medical. Alter holds a research chair in cardiovascular and metabolic rehabilitation at the Toronto Rehabilitation Institute-University Health Network.

American College of Cardiology (ACC) 2018 Scientific Session. Session 1155, Abstract 267. To be presented March 10, 2018.

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