Investigating the seasonal variation of heart failure hospitalizations and in-hospital mortality risks in Japan using a nationwide database

Abstract

Background: Studies have reported seasonal variations in heart failure (HF) hospitalizations and mortality that are observed to peak in the winter, although many of these studies are from Europe or the USA. However, some studies on non-US patients have reported contrasting results. We aimed to determine whether seasonal variation exists in hospitalizations due to HF, investigate the risk of death during hospitalization, and examine possible contributors to such variability in Japan.

Methods: This study was an exploratory analysis of our previous report, which included 269,636 hospitalizations due to HF between 2008 and 2018. The monthly hospitalization rate for HF was evaluated using a linear regression model with April as the reference month. The risk factors for in-hospital and monthly mortality were evaluated using the Cox proportional hazards model.

Results: The hospitalizations due to HF were significantly higher in the winter than in the summer. The peak admission rate occurred in January, and the lowest rate occurred in July. Based on April, changes in the number of hospitalizations per month were estimated using linear multiple regression analysis (adjusted R² = 0.911). The risk of death during hospitalization was lowest in April and gradually increased from August to October (hazard ratio, 1.18-1.21).

Conclusions: There was a significant seasonal variation in HF hospitalizations in Japan. Peak admission rates occurred in January. However, the risk of death during hospitalization was higher in August, September, and October than that in January.

Keywords: Heart failure; Hypertension; Low cardiac output syndrome; Seasonal variation; Winter predominance.