Blood-incompatible infant heart transplants safe, may save more lives

ABO-incompatible heart transplantation (heart transplantation among non-compatible blood groups) can be safely performed in infants a year old or younger, researchers reported at the American Heart Association's Scientific Sessions 2007.

The analysis, based on national data reported to the United Network for Organ Sharing (UNOS), found that transplanting infant hearts across incompatible blood group is as safe as transplantation with compatible blood group types.

“There was no difference in outcome between incompatible and compatible transplantation in these infants,” said Luca A. Vricella, M.D., senior author of the study. “Survival between the two groups was similar at three years.” Nishant Patel, B.A., third-year medical student, presented the study findings at the association's annual conference.

“ABO-incompatible heart transplantation can be performed safely in infants with a low incidence of hyperacute rejection,” Patel said. “ABO-incompatible heart transplantation should be considered in infants to maximize donor organ utilization and reduce mortality among infants.”

Vricella said the impact of using incompatible donor hearts could significantly reduce the number of infants who die while on the waiting list to receive donor hearts.

“Mortality could be reduced by at least 20 percent by using incompatible donors,” said Vricella, chief of pediatric heart transplantation at Johns Hopkins Medical Institutions in Baltimore, Md. “There would be a huge impact on infants who otherwise have to rely on a very small donor pool.”

Up to 40 percent of infants die while waiting for a donor heart. The average wait on the list exceeds two months.

“The whole concept of transplanting infants across blood barriers comes from the necessity to reduce waiting time on the list,” Vricella said.

The study examined data on infant heart transplant recipients reported to UNOS from 1999 to 2007. Of the 591 infants who underwent transplantation, 35 infants (6 percent) received hearts from ABO-incompatible donors. Two ABO-compatible infants died from hyperacute rejection, while no ABO- incompatible infants died from hyperacute rejection.

ABO-incompatibility did not predict mortality. The statistical analysis was adjusted for the different size cohorts, assuring statistical significance.

Survival in both groups reached 75 percent at three years after transplantation. Infants with congenital heart disease (defects existing since birth) represent the predominant group requiring transplantation.

In the study, 71 percent of the incompatible recipients had some form of structural heart disease compared to 66 percent in the compatible group.

Cardiomyopathies, disorders of the heart muscle, represent a second condition requiring transplantation in infants.

Heart function deteriorates until the only option is transplantation. In the study, 11 percent of the incompatible recipients had cardiomyopathy versus 29 percent in the compatible group.

One key reason incompatible transplantation works in infants is the role of antibodies known as isohemagglutinins.

Until age 12 to 14 months, infants have immature immune systems with little or no production of these antibodies. That means they will not have pre-formed antibodies against the donor heart, lowering the risk of rejection.

Vricella said the most challenging transplants are in infants born with structural heart disease, congenital heart anomalies. “These infants are being transplanted as a re-operation, which involves conversion of their anatomy to normal so that they can accommodate the donor heart,” he said.

Vricella said that successful infant heart transplantation means an infant can go home and have a “great quality of life.”