MONDAY, April 28 (HealthDay News) -- Pneumonia, irregular heart beat, and obstructed blood flow to the heart are the most common reasons for hospitalization for heart failure in the United States, researchers say.

A team at the University of California, Los Angeles analyzed data from a heart failure patient registry called the Organized Program to Initiate Lifesaving Treatment in Hospitalized Patients with Heart Failure (OPTIMIZE-HF). Between March 2003 and December 2004, the registry enrolled almost 49,000 patients from 259 hospitals across the United States.

The factors that most often led to hospital admission for heart failure patients were: pneumonia or respiratory ailments (15.3 percent); obstructed blood flow to the heart (14.7 percent); irregular heart beat or arrhythmia (13.5 percent); uncontrolled hypertension (10.7 percent); not taking medications (8.9 percent); worsening kidney function (6.8 percent); and not adhering to a special diet (5.2 percent).

"Over 60 percent of hospitalized heart failure patients had at least one of these precipitating factors at hospital admission," study first author Dr. Gregg C. Fonarow, UCLA's Eliot Corday Chair in Cardiovascular Medicine and Science and director of the Ahmanson-UCLA Cardiomyopathy Center, said in a prepared statement.

Fonarow and colleagues also found that patients with none of these factors had lower in-hospital death rates than those with one or more of the factors. Pneumonia, obstructed blood flow to the heart (ischemia), and worsening kidney function were associated with higher in-hospital death rates and longer hospital stays.

"Understanding the factors that can exacerbate heart failure and lead to hospitalizations -- especially the ones that are avoidable -- are invaluable to help us improve management of heart failure," Fonarow said.

He said this study "offers important insight and points to where we can intervene early, such as making sure patients with heart failure are immunized against flu and pneumonia."

The study was published in the April 28 issue of the journal Archives of Internal Medicine.

"In future studies, we plan to target how specific interventions based on these precipitating factors, such as flu vaccinations, may help this high-risk heart failure population," Fonarow said.