Washington ? Connor Geddes was 13 days old when surgeons gave him a new heart that didn’t match his blood type – deliberately.

Connor, now 11 months old and thriving, is one of several dozen babies around the world to have received mismatched hearts, part of a slowly growing movement to increase these tiniest patients’ survival by taking advantage of a lag in their immune systems.

Now the nation’s transplant network is expanding that effort, saying youngsters may be candidates for an incompatible heart up to age 2.

It’s the first step in a new push by the United Network for Organ Sharing to decrease the number of children who die awaiting an organ transplant, a toll particularly high for infants and toddlers.

“It will not happen overnight,” cautioned Dr. Stuart Sweet of Washington University in St. Louis, chairman of the UNOS pediatric transplant committee. But the new heart guidelines “have the potential for significantly impacting the number of patients who die on the waiting list.”

If the policy sounds counterintuitive, well, it is: Implant a mismatched heart in an adult, and he or she will die rapidly. That happened in 2003, when surgeons in North Carolina accidentally gave a teenager the wrong-type heart and lungs.

But babies’ immune systems must learn to recognize and attack an organ of a different blood type, a process that’s turning out to be more gradual than scientists long thought.

Transplant a heart before the baby starts making antibodies that will attack a mismatched organ, and he or she survives as well as babies given matching hearts, said Dr. Lori West, the Canadian surgeon who pioneered incompatible transplants in Toronto in the late 1990s.

Those babies still need immune-suppressing drugs for life – blood type is just one form of organ rejection.

But given the scarcity of tiny hearts, the mismatch option was good news. In 2005, the last count available, 45 children under age 2 died while awaiting a new heart. As of last month, 74 youngsters under 2 were on the waiting list.

Worry fading

About one in 5,000 children are born with a heart defect so severe that they’ll need a transplant in the first year or two of life. Yet few babies die of conditions that allow their hearts to be donated.

Still, until recently, U.S. transplant centers were reluctant to try mismatched hearts. UNOS began allowing them as a last resort for infants, under age 1, in 2002; only 19 were performed through 2005. The concern: whether children really fare well years after getting a mismatched heart, or if rejection just sets in later.

But in the last year – with some of West’s initial patients now surviving a decade – that worry is fading. Now the question is who’s a good candidate for a mismatched heart, said Dr. Steve Webber, cardiology chief at Children’s Hospital of Pittsburgh.

Connor Geddes, 11 months, has adapted well after receiving a mismatched heart transplant last March. He's shown at home in Erie, Pa., with his mom, Carrie.

“We know we can’t do it in adults, but what’s the cutoff?” Webber asks. “Nobody knows for sure.”

Babies begin producing antibodies to different blood types between 5 months and 2 1/2 years of age – it varies widely from child to child, said West, now at the University of Alberta’s Stollery Children’s Hospital. Only a few of the 90 or so mismatched heart transplants performed worldwide have occurred past a child’s first birthday, the oldest in a 30-month-old in Britain.

Still, age is just a rough marker for antibody production, West stresses. Blood tests to check antibodies are the real key.

Hence the new U.S. policy, adopted last fall and to go into effect later this year. It expands use of mismatched hearts up to age 2, as long as antibody tests show the toddlers are candidates.

For now, many transplant centers are like Webber’s, trying their first mismatched transplants in babies before working up to toddlers.

‘A first step’

Last March, Connor Geddes of Erie, Pa., became Pittsburgh’s first of five such transplants. His heart’s left side was too small to pump. Doctors said Connor wouldn’t live long enough to await a heart that matched his Type A blood, but they had a heart from a Type B donor available.

“It still amazes me,” said Carrie Geddes. “When we talk to people, friends, and tell them, nobody really realizes that can happen.”

Eleven months later, Connor shows no sign of rejection and happily totters after his older brothers. His tracheotomy tube – from lungs weakened by heart-pumping machines while he awaited the transplant – is to be removed soon, and the scar on his chest is barely visible.

UNOS’ Sweet calls the heart policy “a first step in what we really think is a long process in improving wait-list mortality for all children.”

At a first-of-its-kind meeting in March, UNOS will take a hard look at hurdles to improving child organ donation, especially for babies and toddlers. One problem is that when grieving parents consent to a donation, organs aren’t always recovered, perhaps because the local transplant center didn’t immediately see a good recipient, Sweet said.

“It doesn’t mean there is no patient suitable for that organ in the whole United States,” he said. “There are organs out there that if we find the right recipient, they could be transplanted. Even if it’s one at a time, I’m willing to work on that.”