Among patients with heart failure (HF), short-term exposure to both low and high ambient temperatures was associated with an increased risk of all-cause and cardiovascular mortality, with the risk linked to high temperatures intensifying over time, according to a large case-crossover study published Oct. 22 in JAMA Cardiology.

Wenli Ni, PhD, et al., examined data from 250,640 patients with HF in the Swedish National Patient Register who died from any cause between 2006 and 2021. The mean age at death was 84 years and 48% were women. The primary outcome of this analysis was all-cause and cardiovascular death.

The daily mean ambient temperature was assessed at 1 × 1-km spatial resolution. The mean temperature over the 2006-2021 period was low, at 6.63° C. Temperature exposures were expressed as municipality-specific percentiles to account for regional adaptation, with 2.5th and 97.5th percentiles for low and high temperatures, respectively.

Results showed a U-shaped exposure-response curve for short-term temperature and both all-cause and cardiovascular mortality. The odds of all-cause mortality were higher with both low temperature (odds ratio [OR], 1.130) and high temperature (OR, 1.054) exposure for the overall study period.

Regarding cardiovascular mortality, low temperatures were associated with an OR of 1.160 however, high temperatures only demonstrated a significant association from 2014 to 2021 (OR, 1.084).

The researchers note that the increased mortality risk linked to high temperatures over time "underscores the importance of timely adaptation measures, even in high-latitude regions not traditionally considered heat vulnerable."

In other findings, men, individuals with comorbid diabetes and diuretic users showed greater susceptibility to low temperatures, whereas patients with comorbid atrial fibrillation or flutter and those exposed to higher ozone levels were more vulnerable to high temperatures.

In an accompanying editorial comment, Sanjay Rajagopalan, MD, MBA, FACC, et al., write, "This study importantly provides much needed evidence for the urgent need for climate adaptation strategies for at-risk older adult populations… It is time to put the focus back on health in shifting mindsets on climate change."