Clinical Impact of Seasonal and Environmental Factors in Patients with Acute Heart Failure

BACKGROUND: Seasonal factors, particularly during winter, have been associated with worsened heart failure (HF). However, seasonal differences in clinical characteristics, clinical outcomes and environmental mechanisms remain unclear. METHODS: We analyzed 2,857 patients hospitalized for HF. Patients were classified into four groups by season of admission: spring (March to May, n=788, 27.6%), summer (June to August, n= 699, 24.5%), fall (September to November, n=645, 22.6%) and winter (December to February, n =725, 25.4%). Baseline characteristics, clinical outcomes and environmental factors corresponding to the admission month-such as temperature, atmospheric pressure, relative humidity, sunshine duration, influenza activity and PM2.5 concentration-were compared among the groups. RESULTS: The winter group was older and more frequently had hypertension, diabetes, chronic kidney disease and thyroid disease. No seasonal differences were observed in sex, body mass index, HF etiology, other comorbidities, B-type natriuretic peptide levels, or left ventricular ejection fraction. Compared with the fall group, the winter group was associated with higher risk of in-hospital cardiac and all-cause mortality, 90-day cardiac and all-cause mortality (odds ratio 2.13, 1.85, 1.69, 2.01, 1.80, respectively, p<0.05). With respect to environmental factors, (1) lower temperature was associated with 90-day cardiac and all-cause mortality; (2) shorter sunshine duration was associated with 90-day all-cause mortality; and (3) higher PM2.5 concentrations were associated with in-hospital cardiac mortality. In contrast, atmospheric pressure, relative humidity, and influenza activity were not associated with clinical outcomes. CONCLUSIONS: Winter admission for HF was associated with older age, more comorbidities and higher in-hospital and short-term mortality, which may be partly explained by lower temperatures and shorter sunlight.