They analyzed data for two of the most severe congenital heart defects: transposition of the great arteries (TGA), in which the major blood vessels leading between the heart and lungs are switched, and hypoplastic left heart syndrome (HLHS), in which the left side of the heart does not develop properly.
Both defects are lethal if not treated within a few weeks of birth, with operations called the arterial switch operation for TGA and the Norwood procedure for HLHS. Infants may need additional operations later in life, but these initial open-heart procedures are critical for their survival.
The study shows that an infant’s risk of dying in the hospital during or after their operation varied greatly depending on the number of each procedure performed that year at the hospital where they were treated. Mortality rates ranged from more than 10 percent to less than 1 percent for the arterial switch operation, and from more than 35 percent to around 10 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,” says Hirsch, a Lecturer in the Section of Cardiac Surgery at the U-M Medical School who performs operations at the U-M C.S. Mott Children’s Hospital. “For the Norwood, the trend to decreased mortality did not level off.”
The researchers chose the two conditions for their study not because the operations themselves vary in difficulty — both require skilled surgeons and operating room teams — but because of differences in the difficulty of pre- and post-surgical care. TGA care is considered somewhat less tricky than HLHS care. Even after the Norwood operation, babies with HLHS will still need at least two more operations in their first years of life to palliate their defect.
“All of the surgeons who operate on congenital heart defects are incredibly well trained,” says Hirsch, noting that pediatric cardiac surgeons must complete more than 10 years of surgical training after four years of college and four years of medical school to operate on the tiny hearts of infants and children. “It’s a matter of exposure to these complex cases not just for the surgeon, but also for the anesthesiologist, the surgical nurses and perfusionists, the intensive care unit staff, and the social workers and floor nurses who help prepare parents to take care of these children at home.”
The new results suggest that for these most rare and complex of cases, infants have the best outcomes when treated at hospitals whose teams are accustomed to caring for TGA and HLHS babies. The Michigan Congenital Heart Center, for example, handles more than 60 Norwood cases and 20 arterial switch cases each year, along with hundreds of other children with lesser defects.
Selectively regionalizing the care of these more severely ill infants, the researchers conclude, may be warranted based on the difference in mortality seen in the new study. But making sure that babies get to the most experienced centers in time for their operation will require commitments of resources and logistics, and a commitment by smaller congenital heart programs to refer the most complex patients early.
More research is also needed on the factors that influence a baby’s likelihood of dying after being discharged from the hospital following a Norwood procedure, but before he or she has the second- or third-stage operations for HLHS. Currently, this inter-stage mortality is estimated at 15 percent. The U-M has launched a new effort — the Michigan Congenital Heart Outcomes Research & Discovery program — that will allow researchers to collect and analyze much more detailed data about U-M congenital heart patients than ever before, to help answer these questions and more.
The newly published study differs in several major ways from previous studies that examined the relationship between in-hospital mortality and hospital volume for congenital heart patients. Other United States studies, performed in the 1990s when congenital heart operations and post-surgical care were still evolving at a rapid pace, used data for all heart conditions in one or two states.
Although these studies found a relationship between the number of infants treated and their risk of dying, the major thresholds were seen at the 100- to 200-patient level. Hirsch and her colleagues note that these studies included data from patients with much less severe heart defects, who had operations that carry a much lower risk of death during and after surgery.
“For the more routine congenital heart surgery, outcomes are excellent everywhere,” says Hirsch. “But when it comes to a child with a complex defect, it’s important to send him or her to a center of excellence. And the parents of these children are often so overwhelmed by their sudden situation, it will be important to develop the systems and support that will help them get to the right place.”
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In addition to Hirsch, the paper’s authors are pediatric heart surgeon Richard G. Ohye, M.D., and James Gurney, Ph.D. and Janet Donohue, MPH of the U-M Child Health Evaluation and Research Unit. More information on the Michigan Congenital Heart Center is at www.med.umich.edu/cvc/mchc. |
