Dec. 18 (HealthDay News) -- Babies with congenital heart defects are more likely to survive if they're treated at a hospital with the most experience in treating such cases, U.S. researchers conclude.

Researchers at the University of Michigan analyzed figures from the 2003 Kids' Inpatient Database, which is sponsored by the U.S. Agency for Healthcare Research and Quality and includes information on children hospitalized in 36 states.

The study authors focused on two of the most severe congenital heart defects: transposition of the great arteries (TGA), in which major blood vessels leading between the heart and lungs are reversed; and hypoplastic left heart syndrome (HLHS), in which the left side of the heart does not develop properly.

If heart surgery isn't done within a few weeks of birth, both conditions are fatal. An arterial switch operation is used for TGA and an operation called the Norwood procedure is used to correct HLHS.

Reporting in the online edition of Pediatric Cardiology, the team found that the risk of an infant dying in a hospital during or after one of these operations varied greatly depending on the number of these procedures performed at a hospital. Death rates ranged from less than 1 percent to more than 10 percent for the arterial switch operation, and from around 10 percent to more than 35 percent for the Norwood procedure.

"The relationship between hospital volume and risk of dying was significant across the spectrum for both defects, though in the case of arterial switch operations, the difference dwindled among hospitals that performed about 15 or more in a year," study author Dr. Jennifer Hirsch, a pediatric cardiac surgeon, said in a prepared statement.

SOURCE: University of Michigan Health System, news release, Dec. 17, 2007