County-level modeled extreme heat risk and premature all-cause mortality related to cardio-kidney-metabolic syndrome in the United States: A cross-sectional analysis

Background: The aim of this study was to evaluate the association between extreme heat waves and age adjusted cardio-kidney-metabolic (CKM) all-cause mortality rate in the US. Methods: In this cross-sectional study, the county level age adjusted CKM premature (age 65 years) all-cause mortality rate (CKM aaMR) was collected from the Center for Diseases Control (CDC) WONDER (Wide-ranging Online Data for Epidemiologic Research) (2010-2019). The primary exposure was the 2023 US Federal Emergency Management Agency heat wave risk index (HWRI), a marker of extreme heat event frequency. Counties were grouped by the quartile (Q) of their HWRI. Generalized linear models with a Poisson rate regression were fitted to evaluate the association between CKM aaMR and HWRI quartiles adjusting for county-level median age, percentage of ethnic minorities, prevalence of hypertension, diabetes, obesity, coronary artery disease, and stroke; results were reported as incident rate ratios (IRR) and 95 % confidence intervals. Results: Out of 3243, we included data from 2834 (90 %) counties. The median (25th - 75th percentile) CKM aaMR was 64 (47 -85) 15 deaths per 100 000 residents. The county-level median HWRI was 56.4 (32.0, 78.1). Nationwide, compared to counties in HWRI Q1, those in Q2 [IRR 1.03(0.99, 1.06); p 0.1], Q3 [IRR 1.05 (1.01, 1.08); p 0.01], and Q4 [(IRR 1.09 1.05, 1.12); p 0.001] were associated with higher for CKM aaMR. Conclusions and Relevance: In the US, counties at more risk to experience extreme heat events were noted to have higher rates of age adjusted cardio-kidney-metabolic syndrome all-cause mortality rates.