Seasonal variations in hospitalizations of heart failure patients: a United States nationwide analysis

BACKGROUND: Heart failure (HF) remains a leading cause of hospitalization globally, exerting significant strain on healthcare systems and impacting patients' quality of life. Seasonal changes in climate and temperature are known to affect HF-related outcomes. This study investigates the seasonal variations in hospitalization outcomes among HF patients in the United States. METHODS: We conducted a retrospective analysis of the National Inpatient Sample (NIS) database, focusing on patients aged over 18 years with a primary diagnosis of HF from 2018 to 2020, using the ICD-10-CM codes. Our primary outcomes of interest included trends in clinical characteristics, inpatient mortality rates, and length of hospital stay (LOS). In addition, inflation-adjusted healthcare costs for each patient were also analyzed. Statistical analyses included weighted logistic and linear regression, adjusting for patient-level factors (age, sex, race, comorbidities, insurance type, and median household income) and hospital-level factors (bed size, region, and teaching status). Inpatient mortality, length of stay, and inflation-adjusted hospital costs were analyzed. Mortality risk factors were assessed using multivariate models, with costs converted to 2019 dollars using standardized inflation adjustments. RESULTS: We identified 3,820,865 weighted HF hospitalizations, with peak admissions in winter (32.20%), followed by spring (29.73%), autumn (28.68%), and summer (9.39%). The mean patient age was highest in winter (69.5±0.06 years) and lowest in summer (68.7±0.07 years), P<0.001. Comorbidities showed seasonal variations, with hypertension, diabetes, and obesity more prevalent in summer, while acute myocardial infarction was more frequent in winter. White, Hispanic, and Asian/Pacific Islander patients experienced higher winter hospitalizations, whereas Black patients had increased admissions in autumn. Hospitalizations were most common among patients in the lowest income quartile (33.23%). The overall in-hospital mortality rate was 2.28%, highest in winter (2.40%) and lowest in summer (2.11%), P<0.001. The average length of stay (LOS) was 5.24 days (95% CI: 5.20-5.28), increasing from 5.19 days (95% CI: 5.12-5.25) in 2018 to 5.31 days (95% CI: 5.25-5.38) in 2020. Inflation-adjusted costs rose from $57,166 in 2018 to $65,961 in 2020, with significant seasonal differences. CONCLUSIONS: Seasonal variations markedly influence HF-related hospitalizations and outcomes, with winter showing the highest hospitalization and mortality rates, especially among White, Hispanic, and Asian/Pacific Islander patients.