TOPLINE:

In patients with heart failure (HF), short-term exposure to both low and high temperatures was associated with increased odds of all-cause and cardiovascular disease mortality, with the risk linked to high temperatures rising over time.

METHODOLOGY:

• Researchers conducted a case-crossover study to assess whether short-term exposures to low and high temperatures were linked to mortality among patients with HF.
• They analyzed data from 250,640 Swedish patients with HF who died from any cause between January 2006 and December 2021 (mean age at death, 84.3 years; 48.3% women).
• The daily mean ambient temperature was assessed at a 1 x 1-km spatial resolution across Sweden and was expressed as municipality-specific percentiles, with 2.5th and 97.5th percentiles for low and high temperatures, respectively.
• Short‑term exposure included cumulative temperature in the 0 to 6 days before death. Exposures were compared with the minimum mortality temperature, defined as the temperature at which mortality was lowest.
• Primary outcomes were all-cause and cardiovascular disease mortality.

TAKEAWAY:

• The odds of all-cause mortality were higher with exposure to low temperatures (odds ratio [OR], 1.130; 95% CI, 1.074-1.189) and high temperatures ( OR, 1.054; 95% CI, 1.017-1.093) than with exposure to the minimum mortality temperature.
• The risk for mortality associated with high temperatures intensified during 2014 to 2021 (OR, 1.082; 95% CI, 1.029-1.138).
• For cardiovascular disease mortality, low temperatures were consistently associated with an elevated risk (OR, 1.160; 95% CI, 1.083-1.242); however, high temperatures showed a significant association only in 2014-2021 (OR, 1.084; 95% CI, 1.014-1.159).
• Men, those with comorbid diabetes, and diuretic users showed greater susceptibility to low temperatures, and patients with comorbid atrial fibrillation or flutter and those exposed to elevated levels of ozone were more vulnerable to high temperatures.

IN PRACTICE:

"The observed rise in mortality risk associated with high temperatures over time underscores the importance of timely adaptation measures, even in high-latitude regions not traditionally considered heat vulnerable," the researchers wrote.

"The findings from this study are also consistent with climate-mortality projections, which indicate a progressive increase in heat-related mortality both in terms of attributable numbers and fractions, regardless of whether this is driven by climate or demographic trends of an aging global population, increasingly burdened with HF," experts wrote in an editorial accompanying the article.

SOURCE:

This study was led by Wenli Ni, PhD, of Harvard T.H. Chan School of Public Health in Boston. It was published online on October 22, 2025, in JAMA Cardiology.

LIMITATIONS: 

Outdoor temperatures may misclassify personal exposure, especially for older patients who mostly stay indoors. This study was observational and did not imply that the temperatures caused mortality. Lack of ejection‑fraction data prevented assessment by HF phenotypes.

DISCLOSURES:

This study received funding from the European Union's Horizon 2020 research and innovation program. One author reported his institution receiving consulting fees from several pharmaceutical and healthcare companies, including Alleviant, AstraZeneca, and Novartis.

This article was created using several editorial tools, including AI, as part of the process. Human editors reviewed this content before publication.