Critical temperature thresholds for identifying vulnerability to heat-related excess cardiovascular morbidity and mortality
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Background
Extreme heat is a known environmental hazard linked to increased cardiovascular disease (CVD) morbidity and mortality, yet most studies fail to evaluate both acute and long-term effects. We assessed heat-related CVD, and its subtypes: coronary heart disease (CHD), myocardial infarction (MI), and stroke, morbidity and mortality across multiple temporal scales, identifying critical temperature thresholds for short- and long-term exposure.
Methods
We analyzed neighborhood-level death and emergency department (ED) visit records for CVD in Chicago from 2011–2022, linked to sociodemographic characteristics and temperature and humidity estimates. Using generalized additive models with smooth splines, we estimated excess heat-related rates across daily, monthly, and annual temporal scales. We applied K-means clustering and principal component analysis to classify Chicago community areas by heat vulnerability.
Results
Higher temperatures were significantly associated with increased cardiovascular mortality across all temporal scales, but not morbidity. Daily maximum temperatures ≥101.3°F were linked to 0.098 excess CHD deaths per 100,000 (95% confidence interval [CI]: 0.092–0.104, p=0.037), while a 3-day average ≥100.4°F corresponded to 0.109 excess CVD deaths per 100,000 (95% CI: 0.084–0.139, p < 0.001), which may lead to ≈3 daily CVD deaths in Chicago are heat-related during days above 100°F. Monthly associations were also seen for CHD mortality (3.30 excess deaths per 100,000, [95% CI: 2.91–3.66], p=0.001). No significant associations were found for MI or stroke. Mortality clustering revealed four distinct vulnerability profiles, with variation linked to socioeconomic and racial/ethnic characteristics.
Conclusions
We identified critical temperature thresholds associated with cardiovascular mortality across temporal and spatial scales. Findings support targeted public health interventions, including heat warning systems and adaptive strategies, tailored to community vulnerability.
