Upward Air Temperature Shifts and Acute Cardiovascular Events in Individuals with Atherosclerotic Cardiovascular Disease: A Time-Stratified Case-Crossover Study

Background: Global warming is an increasing health concern. While the health impact of heat has been widely studied, the effects of transient temperature fluctuations remain largely unknown. Here we evaluated the impact of upward air temperature shifts (uTS) on acute cardiovascular events and mortality in individuals with atherosclerotic cardiovascular disease (ASCVD). Methods: This time-stratified case-crossover study included 1,315,553 patients with ASCVD from a German health insurance between 2012 and 2020. Daily mean outside temperatures was estimated on a 1 × 1 km grid and, together with daily counts for acute coronary syndrome (ACS; n = 126,193), stroke (n = 154,122), hospitalizations for heart failure (n = 356,053), and all-cause mortality (n = 345,907), aggregated at the 3-digit postcode level. uTS was defined as days when mean air temperature exceeded the preceding seven-day average. Conditional Poisson regression was used to estimate acute and lagged associations, adjusting for time-varying confounders; area-specific estimates were pooled using multivariate meta-analysis. Findings: A 5 °C increase in uTS (observed on 185 days during the study period; 21 days/year), was associated with a higher risk for ACS (relative risk [RR] 1.03; 95% confidence interval [CI], 1.02-1.04), stroke (RR 1.02; 95% CI, 1.01-1.03), hospitalization for heart failure (RR 1.01; 95% CI, 1.01-1.02), and all-cause mortality (RR 1.03; 95% CI, 1.02-1.04). Associations were more pronounced during the warm season. The mean number of deaths attributable to uTS was 23 per 100,000 participants per year (95% CI, 18-29). Interpretation: . Public health action is warranted, given the projected increase in temperature variability with climate change. Funding: This work was supported by a grant from the German Heart Foundation, grant no F/58/21 and the Bavarian State Ministry of Health and Care through the research project DigiMed Bayern (www.digimed-bayern.de), grant no DMB-1805-0001.