Dr. David P. Kao of the University of Colorado School of Medicine and colleagues analyzed nearly 1 million heart failure admissions over 14 years and identified peaks in admissions and mortality.
Seasonal, weekly and hourly variations had been observed in heart failure admissions but the reasons are unclear, Kao said.
Data from all hospitals in the state of New York from 1994-2007 were analyzed. A greater number of factors were included in the analysis than before so that the researchers could confirm or refute previous theories on the reasons behind variations in heart failure morbidity and mortality, Kao said.
The study found daily heart failure admissions increased significantly in January, Fridays and at night. Conversely, the odds were better on Mondays and being admitted in the morning.
"The fact that patients admitted right before the weekend and in the middle of the night do worse and are in the hospital longer suggests that staffing levels may contribute to the findings," Kao said in a statement.
The findings were presented at the Heart Failure Congress in Lisbon.