Heat Alerts and Acute Myocardial Infarction Admissions and Mortality: A Nationwide Registry-Based Cohort Study

Background: Increasingly frequent extreme heat and heat wave events have been associated with various cardiovascular outcomes; currently, the evidence about their impact on acute myocardial infarction (AMI) incidence and mortality remains heterogeneous. In particular, the effects of officially declared heat alert periods on AMI admissions and longer-term mortality have not been consistently characterized using nationwide patient-level data. Methods: We conducted a retrospective, nationwide, registry-based cohort study using data extracted from the Hungarian Myocardial Infarction Registry. All patients with an acute myocardial infarction event between January 1, 2018, and June 16, 2021, were included (n = 30,883). Individual events were linked to daily meteorological data and officially declared heat alert periods issued by national public health authorities. Study outcomes were (1) daily and monthly counts of first hospital admissions for AMI and (2) cumulative all-cause mortality during follow-up. Associations between heat alert exposure, infarction characteristics (STEMI vs. NSTEMI; Type 1 vs. Type 2 MI), and mortality were assessed using descriptive statistics and multivariable logistic regression. Results: The mean age of the cohort was 67.2 years, and 60.3% of patients were male. NSTEMI accounted for 58.0% and STEMI for 42.0% of events. Mean daily AMI admissions were higher during official heat alert periods compared with non-alert summer days, most prominently during the summer of 2018. During follow-up, cumulative all-cause mortality was substantially higher among patients with NSTEMI than STEMI and markedly elevated among patients with type 2 myocardial infarction. The strongest predictors of the mortality in the multivariate analysis were age, prior myocardial infarction, diabetes mellitus, heart failure, and infarction type. Therefore, we found that heat alert exposure was associated with a modest but statistically significant increase in the odds ratio of cumulative mortality. Conclusions: Officially announced heat alert periods were associated with increased acute myocardial infarction admissions but contributed only modestly to cumulative mortality risk during follow-up. Long-term outcomes after AMI were driven predominantly by infarction type and established cardiovascular risk factors rather than heat exposure alone.