Short-term exposure to low and high temperatures and mortality in heart failure patients: a nationwide study in Sweden

Background Heart failure patients may be particularly susceptible to non-optimal temperature exposures due to compromised physiological functions. However, the associations between short-term exposures to low and high temperatures and all-cause mortality in patients with heart failure remain unclear. Purpose We aimed to assess the associations between short-term exposures to low and high temperatures and all-cause mortality among patients with heart failure in Sweden. Methods This nationwide study analyzed all-cause mortality in 250,640 heart failure patients in Sweden between 2006 and 2021, using data from the Swedish National Patient Register and Cause of Death Register. Daily mean ambient temperatures (modeled a 1 × 1 km spatial resolution) were linked to patients’ residential Regional Statistical Areas (RegSO). We applied a time-stratified case-crossover design and used conditional logistic regression with a distributed lag non-linear model to investigate the associations between low and high temperature exposures during the 1-week period preceding a death event (lag 0-6 days) and all-cause and cardiovascular mortality in heart failure patients. Temporal variations in these associations were assessed by comparing data from 2006-2013 to that from 2014-2021. We also examined potential effect modification by comorbidities, medication use, and air pollution levels. Results The relationship between short-term exposure to daily air temperature and all-cause mortality in heart failure patients exhibited a U-shaped pattern (Figure 1). The odds ratios for all-cause mortality in heart failure patients were 1.130 (95% CI: 1.074-1.189) for low temperatures at the 2.5th percentile and 1.054 (95% CI: 1.017-1.093) for high temperatures at the 97.5th percentile, compared to the Minimum Mortality Temperature, corresponding to the 84th percentile of temperature distribution. Similar U-shaped patterns were observed for cardiovascular mortality. Notably, the slopes of the all-cause and cardiovascular mortality risk curves for high temperatures were steeper and exhibited a more rapid increase in 2014-2021. Heart failure patients comorbid with diabetes and those using diuretics were found to be more susceptible to low temperatures. Conversely, high temperatures showed a stronger association with all-cause mortality among individuals exposed to higher ozone levels. Conclusions Our nationwide study in Sweden indicates that short-term exposure to low and high temperatures is associated with an increased risk of all-cause and cardiovascular mortality in heart failure patients. Notably, the steepening slope of mortality risk associated with high temperatures over time suggests that the threat posed by heat to heart failure patients may be growing.