Effect of heatwaves on daily hospital admissions and premature mortality in Poland: A 10-year observational study (PL-PARTICLES Study)

Abstract Introduction Climate change has led to more frequent, intense, and prolonged heatwaves. Although the effects of high temperatures on cardiovascular diseases (CVD) and premature mortality have been widely researched, their comprehensive impacts remain insufficiently studied. Purpose To assess the relationship between heatwave days and acute hospital admissions due to CVD, as well as premature mortality, at the county level, considering different age groups. Methods Geospatial analysis was conducted on the EP-PARTICLES cohort, comprising residents of Eastern Poland (N=8,077,671), with over 5 million CVD hospital admission records and deaths from 2011 to 2020, obtained from the National Health Fund. Heatwave events were indexed using the Excess Heat Factor (EHF) at the level of 709 counties (LAU–2). Additional covariates included air pollution, humidity, atmospheric pressure (as smoothed functions), weekdays, months, public holidays, and indicator varables. Negative binomial regression models were used at the municipal level. Results Total recorded deaths were 831,246 (total mortality, TM; median age: 78 years, IQR: 65–86, 52.8% male), including 377,344 cardiovascular-specific deaths (CVD mortality; median age: 82 years, IQR: 72–88, 46.2% male). In the non-adjusted model, TM increased by 4.8% (95% CI: 3.5–6.1), with a stronger effect in younger individuals (<65 years: 9.3%, 95% CI: 6.7–12.0) compared to older (≥65 years: 3.3%, 95% CI: 1.8–4.8), yielding a ratio of IR of 2.82 (P < 0.001). CVD mortality increased by 3.6% (95% CI: 1.8–5.6), with a higher effect in younger individuals (8.0%, 95% CI: 2.9–13.3) compared to older (3.0%, 95% CI: 1.0–5.0), ratio of IR: 2.67 (P=0.003). NSTEMI admissions decreased by −12.3% (95% CI: −15.9 to −8.5), with the largest reduction observed in the elderly (−16.8%, 95% CI: −21.1 to −12.2). No significant impact of heatwaves on the number of hospital admissions for ischemic stroke was observed. AKI admissions increased substantially by 15.9% (95% CI: 10.5–21.5), with stronger effects in younger individuals (35.9%, 95% CI: 24.1–48.8, P < 0.001) compared to older (11.2%, 95% CI: 5.2–17.5), resulting in a ratio of IR of 3.20 (P <0.001). Models adjusted for NO2, O3, and PM2.5 showed consistent effect directions for most outcomes, with adjustments for O3 yielding the highest estimates, particularly for TM and CVD mortality. Conclusion Heatwaves are significantly associated with increased mortality and cases of acute kidney injury but are linked to reductions in hospitalizations for acute coronary syndromes. The observed decrease in hospitalizations for myocardial infarction and no effect in IS could be indicative of increased pre-hospital mortality during heatwave events, as individuals experiencing severe cardiac events may succumb before reaching medical facilities. These findings highlight the importance of targeted public health strategies to address the diverse impacts of heatwaves on cardiovascular outcomes.