This finding surprised the researchers and may have significant implications for patient outcomes, medical costs and care.
People with secondary CHF those who were admitted to the hospital for another reason were more likely to die than were those diagnosed with primary CHF, incurred more medical costs and spent more time in the hospital.
The study included a year's worth of inpatient records from more than 2.5 million people admitted to 350 hospitals in the United States . More than half a million of these patients were diagnosed with CHF.
"We expected to see some patients with secondary congestive heart failure, but we didn't think that the vast majority of congestive heart-failure cases would fall into that category," said Joseph Dasta, a study co-author and a professor of pharmacy at Ohio State University .
Congestive heart failure is a serious condition in which the heart doesn't pump blood as efficiently as it should, leading to a buildup of fluids in body tissues.
Dasta and his colleagues presented their findings in May in Washington , D.C. , at the American Heart Association's Sixth Scientific Forum on Quality of Care and Outcomes Research in Cardiovascular Disease and Stroke.
The researchers used a healthcare database that contained information on patients admitted to 350 hospitals in the United States in 2003. They wanted to know what resources were used to treat people with CHF as well as the costs affiliated with treating those patients.
Of the 2.5 million people admitted to the hospitals that year, one in five (20 percent, or 498,713) had a CHF diagnosis. Of those, 73.7 percent (367,656) were diagnosed with secondary CHF.