Abstract 4365394: Impact of Temperature on the Incidence of Pulmonary Embolism: A Nationwide 10-Year Registry Study in Japan.

Background: Previous studies from Western countries have reported associations between environmental temperature and pulmonary embolism (PE), with increased risk in colder seasons. However, large-scale studies have not yet been conducted in East Asia. Research Questions: We hypothesized a U-shaped association between temperature and PE incidence, with temperature sensitivity varying across clinical subgroups, assuming that cold temperatures might also increase PE risk in Japan. Methods: We analyzed data from the Japanese Registry Of All cardiac and vascular Diseases (JROAD)-DPC inpatient database (2012–2021), covering nearly all acute-care hospitalizations in Japan (~6 million/year). A total of 63,354 emergency admissions for acute PE were identified. Mean age was 69 ± 16 years; 42% male, 17% with cancer, 13% with diabetes, 16% with dyslipidemia, and 30% with hypertension. Weather data (mean/max/min temperature, humidity, pressure, sunshine, wind) were obtained from the Japan Meteorological Agency and linked to admission dates by region. Univariable and multivariable logistic regression were used to evaluate associations between PE risk and meteorological factors. Subgroup analyses were conducted for season, temperature shocks (≥5°C change in 24h), extreme days (≥30°C or ≤0°C), and cancer or shock status. PE incidence per 10 million population was calculated using prefectural population data, and cubic spline models were used to visualize the temperature–PE relationship. Results: Lower mean temperature (OR 1.02 per 1°C decrease; 95% CI 1.01–1.03), cold shock (OR 1.05; 95% CI 1.02–1.08), and hot shock (OR 1.04; 95% CI 1.01–1.07) were associated with increased PE risk. In winter, lower temperatures increased PE risk (min temp OR 1.009; p<0.001); in spring, higher temperatures were linked to increased risk (min temp OR 1.025; p<0.001). Hot days (OR 1.13; 95% CI 1.05–1.22) and cold days (OR 0.87; 95% CI 0.81–0.94) were also significantly associated with PE. Spline analysis confirmed a U-shaped association, with lowest risk at ~20°C. Patients without cancer or shock were more temperature-sensitive, while those with cancer or shock had persistently high PE incidence year-round. Conclusion: This nationwide study in Japan identified a U-shaped association between temperature and PE incidence. Patients without cancer or shock showed clear weather sensitivity, whereas those with cancer had elevated year-round risk.