Short-term effects of ambient temperature variability on myocardial infarction hospitalizations in Sweden: A nationwide case-crossover study

Abstract

Abstract Background Climate change threatens human health and general welfare via multiple dimensions. However, the short-term effect of temperature variability, a crucial aspect of climate change, on myocardial infarction (MI) remains largely unexplored. Purpose We aimed to assess the short-term effects of temperature variability on MI hospitalizations within the nationwide SWEDEHEART registry. Methods This population-based nationwide study involved 228,897 MI patients from the SWEDEHEART registry in Sweden from 2005 to 2019. High-resolution (1 km × 1 km) daily mean ambient temperature was estimated using a spatiotemporal machine learning methodology and assigned to patients’ home addresses. Temperature variability was calculated as the difference between the same-day (as the MI event) ambient temperature and the average temperature recorded over the preceding seven days. Specifically, an upward temperature shift represents a rise in the current day’s temperature relative to the seven-day average, while a downward temperature shift indicates a corresponding decrease. A time-stratified case-crossover design incorporating a conditional logistic regression model with distributed lag non-linear model was applied to estimate the association between ambient temperature variability and total MI, ST-segment elevation myocardial infarction (STEMI) and non-ST-segment elevation myocardial infarction (NSTEMI). Moreover, we assessed potential effect modification by sex and medication intake. The results were expressed as odds ratio (OR, with their 95% confidence intervals [CIs]) per 1°C increase in temperature variability. Results Our study found that a 1°C increase in upward temperature shift was significantly associated with increased risks for total MI, STEMI, and NSTEMI (OR [95% CI]: 1.010 [1.006-1.015], 1.014 [1.006-1.022], and 1.009 [1.004-1.014], respectively). Furthermore, a 1°C greater in downward temperature shift was significantly associated with decreased risks for total MI and NSTEMI (OR [95% CI]: 0.995 [0.991-0.999], and 0.993 [0.988-0.998], respectively). Moreover, we found that males and patients who were on any heart medication, particularly digitalis, were at a higher risk of MI associated with exposure to higher upward temperature shifts compared to females and their counterparts not taking these medications. Conclusions This nationwide case-crossover study provides novel evidence that short-term exposure to increasing upward temperature shift is associated with an increased risk of MI hospitalization. Our finding highlights the cardiovascular health threats posed by upward temperature shifts, which are anticipated to increase in frequency and intensity due to climate change.