Heart transplant patients are as much as 25% more likely to survive if the sex of the donor is the same as the patient’s, researchers said Wednesday.

The results surprised experts because, for most types of transplants, sex differences are irrelevant as long as a good immunocompatability is achieved.

The worst results were in men who received hearts from smaller women, suggesting that the pumping capacity of the organ is crucial to the success of the procedure, according to the study, presented at a New Orleans meeting of the American Heart Assn.

But women were also somewhat more likely to reject transplants from males, perhaps because of lingering immune stimulation from earlier pregnancies, experts said.


The findings may not make much difference to transplant procedures, however, because the relatively small number of hearts that become available grossly limits the surgeon’s ability to pick and choose.

“Organs are scarce . . . so we must take the next organ that is available,” said Dr. Jon Kobashigawa, director of the heart transplant program at the Ronald Reagan UCLA Medical Center. And a heart can only be kept out of the body for no more than six hours.

There are many factors that could improve survival, he said, if surgeons had more time to make a match.

About 2,200 heart transplants are performed each year, but an additional 2,700 patients are on waiting lists, according to the United Network for Organ Sharing, or UNOS, which manages the lists. Three-quarters of all heart transplants are given to men, so by necessity many must receive female organs.


Dr. Eric Weiss of Johns Hopkins University in Baltimore studied UNOS records for 18,240 heart transplants that took place between 1998 and 2007. Some patients were followed for as long as 10 years, with the average being 3.4 years.

Overall, 71% of the patients -- 77% of males and 51% of females -- in the federally funded study received a heart from a donor of the same sex.

About a quarter of the transplant patients died during the study.

When the sexes of the donor and recipient matched, the researchers observed:


* A 13% lower risk of graft rejection in the first year.

* A 14% lower risk of rejection over the entire length of the study.

* A 25% drop in death during the first 30 days after transplant.

* A 20% lower rate of death in the first year.


“We hypothesized that we would see a big difference in the short-term survival -- which we did, most likely because of heart-size issues -- but what was interesting was the substantial difference in the long term, as well,” Weiss said.

The results were similar to data on 8,000 patients from an international study compiled by the International Society for Heart & Lung Transplantation, Kobashigawa said. In that study, however, all the patients were followed for at least 10 years.

The primary difference between the two studies was that among the international patients, women who received organs from women also did not do as well in the long term.

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thomas.maugh@latimes.com