The seasonal variation in hospitalizations due to chronic systolic heart failure correlates with blood sodium levels and cardiac function.

Background: Although seasonal variation in hospitalizations due to chronic heart failure is recognized, the possible contributors to such variability are less well documented.

Methods: Records from all admissions to 12 hospitals in Hubei province, China, over a 10-year period with diagnostic codes for chronic systolic heart failure (CSHF) were reviewed. A total of 16,145 patients with CSHF were analyzed.

Results: There was a marked seasonal variation in the number of hospitalizations due to CSHF, with two peaks in the monthly rate of hospitalization due to CSHF occurring in December and August compared with the spring and autumn months. Monthly hospitalizations due to CSHF for patients with New York Heart Association class III and IV ranged from a peak of 40.4% and 23.3% above average in December and August, respectively, to 18.6% below average in November, while hospitalizations due to CSHF for patients with New York Heart Association class I and II exhibited no obvious seasonal variation. Blood sodium level (95% CI 2.132 to 2.144; P=0.036) was an independent risk factor for hospitalizations due to CSHF in August.

Conclusion: The number of hospitalizations due to CSHF increased during the colder and warmer months in China. A low blood sodium level was associated with the peak in hospitalizations in August.