‘Unprecedented pace’ of extreme temperatures associated with death from common CV conditions
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A multinational data set across climate zones suggests an association between extreme hot and cold temperatures and CV cause-specific mortality, with the largest excess deaths associated with HF, researchers reported.
“We estimated that for every 100 CV deaths, at least one additional death is from extreme cold and hot days,” Barrak Alahmad, MD, PhD, MPH, research fellow at Harvard T.H. Chan School of Public Health and faculty member at Kuwait University College of Public Health, told Healio. “If a person has heart disease, it is prudent to take special precautions during extreme weather events to protect the health of your heart. Such precautions include hydration, avoiding outdoor exposure, seeking thermal comfort and many other measures.”
Alahmad and colleagues created a database of daily counts of deaths from specific CV causes from 567 cities in 27 countries across five continents in overlapping periods ranging from 1979 to 2019, using data from the Multi-Country Multi-City (MCC) Collaborative Research Network. Researchers then assessed daily ambient temperatures, obtained from weather stations and climate reanalysis models in the MCC environmental database. The analyses included deaths from any CV cause (32,154,935), as well as deaths specifically attributed to ischemic heart disease (11,745,880), stroke (9,351,312), HF (3,673,723) and arrhythmia (670,859).
“The analyses follow a two-stage approach: At each city, we estimate the association between extreme temperatures and death from a CV cause; and then we pool all the risk estimates from individual cities to get an overall estimate,” the researchers wrote.
To assess CV mortality associations with extreme hot and cold temperatures, researchers fit case-crossover models in each city and used a mixed-effects meta-analytic framework to pool individual city estimates. Extreme temperature percentiles were compared with the minimum mortality temperature in each location. Excess deaths were calculated for a range of extreme temperature days.
The findings were published in Circulation.
At extreme temperature percentiles, heat (99th percentile) and cold (1st percentile) were associated with higher risk of dying from any CV cause, ischemic heart disease, stroke and HF compared with the minimum mortality temperature, which is the temperature associated with least mortality.
Across a range of extreme temperatures, hot days, defined as above the 97.5th percentile, and cold days, defined as below the 2.5th percentile, accounted for 2.2 (95% CI, 2.1-2.3) and 9.1 (95% CI, 8.9-9.2) excess deaths for every 1,000 CV deaths, respectively.
HF was associated with the highest excess deaths proportion from extreme hot and cold days with 2.6 (95% CI, 2.4-2.8) and 12.8 (95% CI, 12.2-13.1) for every 1,000 HF deaths, respectively.
“The topic of climate change and CV health received little attention from cardiologists despite the great advancements in CV prevention research and the abundance of data,” Alahmad told Healio. “Professional cardiology societies need to be on top of environmental exposures, such as extreme temperatures. In this rapidly changing climate and an unprecedent pace of warming, it is not the time to be asleep at the driving wheel.”
For more information:
Barrak Alahmad, MD, PhD, MPH, can be reached at balahmad@hsph.harvard.edu; Twitter: @Barrak1.
Perspective
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This is a very important study highlighting a growing issue, which is the health impacts of a changing climate due to greenhouse gas emissions. This study reinforces previous studies demonstrating an increase in CV events and deaths due to extreme temperatures. The authors also highlight how different types of heart disease deaths, such as MI or stroke, all increase due to extreme temperatures. The finding of increased mortality due to extremely cold temperatures is also concerning, as in certain parts of the world, such as in the United States, climate change may also lead to a higher occurrence of extremely cold days.
A limitation of the study is that cause of death listed on death paperwork can sometimes be unreliable and the finding of increased HF-related deaths due to extreme heat differs from a U.S.-based study, which showed a decline in HF admissions during heat waves. Regardless, this study should be call to arms for CV health care professionals as well as professional societies and public health experts that climate change in general — and extreme temperatures in particular — are a growing public health issues that will disproportionately impact people with preexisting CVD.
Perelman School of Medicine, University of Pennsylvania
Staff Cardiologist, Philadelphia VA Medical Center
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