Cold spells, heat waves, and non-optimal air temperature and risk of heart failure hospitalization in Sweden

Background Extreme temperature events are projected to increase with climate change, yet the associations of short-term exposure to heat and cold with heart failure (HF) exacerbations remain incompletely characterized. Purpose To investigate the associations of short-term exposure to cold spells, heat waves, and non-optimal ambient temperature with HF hospitalization in Sweden. Methods We conducted a nationwide time-stratified case-crossover study including 482,000 HF hospitalizations recorded in the Swedish National Patient Register between 2006 and 2021. Daily mean ambient temperature at 1×1 km spatial resolution was aggregated and linked to patients’ residential areas. Cold spells were defined as ≥2 consecutive days with daily mean temperature below the 5th percentile of the municipality-specific cold-season distribution (October - March). Heat waves were defined as ≥2 consecutive days with daily mean temperature at or above the 95th percentile of the municipality-specific warm-season distribution (April - September). We applied conditional logistic regression combined with distributed lag non-linear models to estimate lag-specific (lags 0-6 days) and cumulative associations of cold spells, heat waves, and ambient temperature with the odds of HF hospitalization. Results During the cold season, cold spells and lower ambient temperature exposures were associated with an increased risk of HF hospitalization at lag 2/3 - 6 days, becoming statistically significant at lags 3 to 5 days. The cumulative associations with HF hospitalization over lags 2-6 were significant for both cold spells (odds ratio [OR] 1.08, 95% confidence interval [CI]: 1.04-1.13) and lower ambient temperature (OR 1.08, 95% CI: 1.05-1.11). During the warm season, higher ambient temperature exposure was associated with increased odds of HF hospitalization at lags 1-3 with attenuation at longer lags; the cumulative association over lags 0-3 was significant (OR 1.10, 95% CI: 1.06-1.13). In contrast, no significant association was observed for heat waves. Conclusion Our Swedish nationwide study indicates that short-term exposure to cold spells, lower temperatures, and higher temperatures is associated with an increased risk of HF hospitalization. The delayed impact of cold and the more immediate impact of heat underscore the need for target prevention and clinical management strategies for patients with heart failure.