The Partial Heart Transplant Because Kids Grow, Valves Don’t

When pediatric cardiac surgeons evaluate options for their smallest patients with the most severe cardiac birth defects, they don’t have a lot of good choices.

For conditions such as truncus arteriosus and severe aortic stenosis without good function, infants not only need new heart valves and arteries to survive, but the new tissue also needs to grow with the baby.

With traditional valve replacements, “kids grow but the valves don’t,” said Taufiek Rajab, MD, a pediatric heart surgeon at the Arkansas Children’s Hospital in Little Rock, Arkansas, who first conceived of the idea of a partial heart transplant. The mortality rate associated with valve replacement is “worse than the mortality of heart transplant.”

That’s why Douglas Overbey, MD, MPH, from the Duke University Medical Center in Durham, North Carolina, has been pioneering a new procedure, called a partial heart transplant, that allows the transplantation of living valves and heart muscle into infants with severe congenital heart conditions. The living tissue grows with the child, eliminating the need for countless repeat operations.

Since 2022, when Overbey performed the first-ever partial heart transplant, 30 surgeries have been performed globally. The procedure is innovative on its own, but both Overbey and Rajab agree that the approach opens doors for children who need new heart valves. Many times, diseased hearts that are removed during transplantation still have functional, intact valves that can be transplanted into others, creating a domino effect of life-saving procedures. For this to happen, however, organ procurement organizations, such as the United Network for Organ Sharing, must develop strategies and regulations so that these surgeries can be performed more regularly.

“There are a lot of different options” for the use of partial hearts, “including the valves and the other tissues of the heart,” Overbey said. “The big issue is logistics.”

The Engineering Marvel of the Heart’s Four Valves

The heart’s four valves are engineering marvels, allowing blood into the heart through the mitral and tricuspid valves and then out again through the pulmonary and aortic valves. Over a lifetime, heart valves open and shut billions of times.

Although heart valve problems are more common with age — an estimated 12.4% of Americans older than 75 years have aortic stenosis — structural heart problems can also occur during embryonic development. One in 100 babies is born with congenital heart disease, according to the Centers for Disease Control and Prevention. The survival of these vulnerable infants has improved dramatically in recent years, but replacing heart valves in young children remains a problem.

Adults have a suite of options available, including mechanical valves and bioprosthetic valves, some of which don’t even require open-heart surgery. For babies and young children, however, these options are not ideal because any artificial valve would require frequent replacement during growth. Surgeons have turned to heart valves from cadavers, but there are also issues with those.

Most transplanted heart valves are decellularized and cryopreserved, stripped of much of the living tissue. This process preserves the valves and prevents immune system rejection, but it also means that the size of the valve is static.

Heart transplantation is an option, but waiting lists are up to 6 months long, especially for neonates. Left ventricular assist devices often don’t work well for children with valve issues, meaning that many do not survive long enough to receive a new heart.

During his training as a pediatric cardiothoracic surgeon at the University of Colorado, Boulder, Colorado, Rajab became painfully aware of these shortfalls. Individual heart valves were always more available than complete hearts. But if an intact heart valve could be transplanted into a child, he hypothesized, it had the potential to grow as the child did, eliminating the need for numerous repeat procedures.

Will An Intact Heart Valve Grow?

Rajab mentioned this idea to Joseph Turek, MD, PhD, a pediatric heart surgeon at Duke Children’s Hospital and Health Center in Durham, North Carolina, when the pair met at a professional conference. Turek was enthusiastic and found Overbey equally optimistic.

“If the valve and conduits are living, then those cells can perform self-repair and we see greater valve durability over time,” Overbey said.

The team began testing the procedure in piglets, a close anatomical match for human children. The actual surgery itself was fairly straightforward, Rajab said.

“There was no technological breakthrough that happened that suddenly made it possible. Once people started transplanting hearts and replacing valves in babies,” partial heart transplant became possible, he explained.

It was a far bigger challenge to coordinate a team of surgeons, cardiologists, anesthesiologists, critical care providers, and veterinarians to help perform the procedure and care for the animal. After several successful attempts, the team was ready to try a partial heart transplant in a human.

The First Procedure

The first procedure was performed in April 2022 on a 17-day-old infant named Owen who had the rare congenital heart defect truncus arteriosus as well as a leaky valve. Owen was too sick to wait for a full heart transplant, so a surgical team — which included Rajab, Overbey, and Turek — transplanted aortic and pulmonary heart valves, along with the surrounding tissue. After 1 year, Owen’s valves were growing with him and he was happy and healthy, the team reported last year in JAMA.

Last month, Duke announced that Overbey and his colleagues had performed the first living mitral valve replacement, a type of partial heart transplant. An 11-year-old girl whose heart was removed for a full transplant donated her old heart’s healthy valves to two girls in North Carolina, one of whom received the functional mitral valve. All three children are doing well, Overbey said.

Partial heart transplants are a medical breakthrough in and of themselves, but also because they provide a range of new, lifesaving options for children with complex congenital heart conditions.

“There’s always going to be a greater supply of valves than hearts,” Overbey explained. “We’ve been trying to do partial transplants for more indications because these do all grow, and we want to see fewer redo heart surgeries.”

Reusing functional valves from children who undergo heart transplantation dramatically increases the availability of living donor valves. As well, transplanting only part of the heart decreases the chance of later organ rejection. It’s a cascade of benefits that Overbey said he sees getting bigger with time.