Temperature-Defined Heat-Alert-Threshold Days and Acute Myocardial Infarction Admissions and Mortality: A Nationwide Hungarian Registry-Based Cohort Study.
Bálint C, Al-Murshedi A, et al. • International journal of environmental research and public health • 2026
Temperature-defined heat-alert-threshold days were associated with fewer recorded AMI admissions during summer (aIRR 0.93, 95% CI 0.90–0.97) but not with differences in post-AMI all-cause mortality (aHR 0.96, 95% CI 0.87–1.05) among hospitalized patients in a nationwide Hungarian registry-based cohort study.
Key Findings
Results
Heat-alert-threshold days were associated with significantly fewer recorded AMI admissions during summer in Hungary.
Adjusted incidence rate ratio (aIRR) of 0.93 (95% CI 0.90–0.97) for AMI admissions on heat-alert-threshold days versus non-alert days during summer.
Heat-alert-threshold days were defined using the Hungarian national heat-health action plan criterion of daily mean temperature ≥25 °C.
Analysis used adjusted quasi-Poisson regression models.
The authors explicitly caution that this inverse association 'should not be interpreted as evidence of a protective effect of heat exposure.'
Results
Heat-alert-threshold day exposure was not associated with differences in cumulative all-cause mortality after AMI hospitalization.
Adjusted hazard ratio (aHR) of 0.96 (95% CI 0.87–1.05), indicating no statistically significant association with post-AMI mortality.
Mortality follow-up extended through 16 June 2021, with AMI admissions from 1 January 2018 to 31 December 2019.
Cumulative mortality was analyzed using stratified Cox proportional hazards models.
Findings remained consistent across sensitivity analyses.
Methods
The study cohort comprised 30,883 AMI events from 29,596 unique patients with a mean age of 67.2 years and a majority of male patients.
Mean age was 67.2 years (SD 12.8 years).
60.3% of patients were male.
Data were drawn from the Hungarian Myocardial Infarction Registry (HMR), a nationwide registry.
All AMI admissions between 1 January 2018 and 31 December 2019 were eligible for inclusion.
Results
Patients admitted on heat-alert-threshold days had baseline clinical characteristics similar to those admitted on non-alert days.
All standardized mean differences (SMDs) for baseline clinical characteristics were less than 0.10 between heat-alert and non-alert admission groups.
An SMD <0.10 is a conventional threshold indicating negligible imbalance between comparison groups.
This balance supports comparability of the two groups for regression analyses.
Discussion
The authors identified several alternative explanations for the observed inverse association between heat-alert-threshold days and AMI admissions, cautioning against a causal interpretation.
Proposed alternative explanations include behavioral adaptation, delayed care-seeking, exposure misclassification, and residual confounding.
Out-of-hospital cardiovascular events were not captured by the registry and may represent unmeasured outcomes.
Administrative heat-alert declarations were not linked to the analytic dataset, so findings reflect associations with the temperature criterion only, not the effectiveness of the Hungarian heat-alert system.
The authors note the possibility that reduced admissions could reflect missed or delayed presentations rather than reduced incidence.
Methods
The study used the temperature criterion from the Hungarian national heat-health action plan as the exposure definition, not actual administrative heat-alert declarations.
Heat-alert-threshold days were operationally defined as days with daily mean temperature ≥25 °C.
Administrative heat-alert declarations were not linked to the analytic dataset.
This distinction means the study evaluates associations with a temperature threshold rather than the real-world implementation or effectiveness of Hungary's heat-alert system.
What This Means
This research examined whether dangerously hot days — defined as days when the average temperature reaches 25°C or above, the threshold used in Hungary's national heat warning system — are linked to more heart attacks and worse survival after a heart attack. Using data from a nationwide Hungarian heart attack registry covering nearly 30,000 patients over two years, the researchers found a counterintuitive result: on the hottest days, slightly fewer heart attack hospital admissions were recorded (about 7% fewer), and survival after a heart attack was no different compared to cooler days.
However, the researchers strongly caution that the drop in hospital admissions during hot days should not be taken to mean that heat is somehow good for the heart. Instead, they suggest several more plausible explanations: people may change their behavior on hot days (staying indoors, resting), some people who have heart attacks on hot days may delay seeking care or not seek it at all, and some people may die outside the hospital before ever being admitted — none of which would be captured in the hospital registry. In other words, fewer recorded admissions may actually reflect missed or delayed presentations rather than fewer actual heart attacks occurring.
This research matters because heat waves are becoming more frequent due to climate change, and understanding how extreme heat affects heart health is important for public health planning. The finding that post-admission survival was similar on hot and non-hot days suggests that once patients do reach the hospital, their outcomes are not measurably worse — but the concern remains that some people may never make it to the hospital during heat events. The study highlights a key limitation of using hospital registries alone to understand the full health impact of extreme heat.
Bálint C, Al-Murshedi A, Jaber A, Pakai A, Verzár Z. (2026). Temperature-Defined Heat-Alert-Threshold Days and Acute Myocardial Infarction Admissions and Mortality: A Nationwide Hungarian Registry-Based Cohort Study.. International journal of environmental research and public health. https://doi.org/10.3390/ijerph23081010