New valves for babies that can grow with them

by Tom Ulrich on October 4, 2012

In children with severe mitral valve defects, sometimes valve replacement is the only option. Expandable mitral valves that can be enlarged as a child grows could make caring for such children less complex and invasive.

The human heart is kind of like a busy factory with two powerful pumps—the ventricles—and two “unloading docks,” called the atria. Together, these chambers maintain a delicate balance, ensuring that oxygen-rich blood moves out into the body and that oxygen-poor blood gets pushed back to the heart and lungs.

Just like any factory, however, the heart’s essential functions can be seriously disrupted if just one piece of machinery isn’t working properly.

The mitral valve is a key part of that mechanical balance. This one-way valve helps move blood from the left atrium into the left ventricle, which then pushes the blood out to the body. A failure of the valve can be life-threatening, but fixing or replacing it in children is incredibly complex—and often requires many repeat operations over time.

But two cardiac surgeons at Boston Children’s Hospital, Sitaram Emani, MD, and Pedro del Nido, MD, may have made the repair a little easier by developing a replacement mitral valve that can expand as a child grows.

If the mitral valve is too narrow—a condition called mitral valve stenosis—blood backs up in the left atrium, with several upstream effects:

  • Added pressure in the left atrium can cause it to enlarge
  • Because the lungs feed freshly oxygenated blood into the left atrium, the pressure can push blood back into the vessels of the lungs
  • Because it has to work harder, the heart can weaken over time

If a grownup has mitral valve stenosis, surgeons typically replace their defective valve with a prosthetic one—a (hopefully) one-time repair that gets their heart working properly again.

With children, and especially newborns and infants, it gets more complicated.

“In some ways, repair of the mitral valve is still more of an art than a science,” says Emani, a pediatric cardiac surgeon at Boston Children’s who specializes in cardiovascular surgery for newborns and children with complex congenital heart disease. “You have to be able to respond to each child’s unique anatomy, and the mitral valve is structurally more challenging from a surgical standpoint than the other valves in the heart. There are a lot of critical structures very close to it that restrict what you can do.”

“In some ways, repair of the mitral valve is still more of an art than a science.”

While surgeons like Emani prefer to fix a child’s existing valve if they can, sometimes it’s just beyond repair. The next step is replacement, which comes with its own set of obstacles.

“Children often outgrow a fixed diameter prosthetic valve within months to years after implantation, requiring multiple replacements over time,” Emani explains. And multiple replacements means multiple surgeries, a huge expense and a huge strain on a child’s growing body. “What we need is a solution that would allow us to expand a valve as a child grows and avoid taking them back into the operating room.”

That’s when he and his colleagues noticed something about the Melody valve, an expandable prosthetic valve currently used in children who need a new pulmonary valve.

While the Melody is meant to be used at its full size, the pair noted that it still functions even when only partially expanded, opening the door to using it in infants and babies. By trimming the length of the replacement valve and cinching it down to its smallest size, Emani has been able to implant it into five children to date ranging from two months to six months old. He reported his team’s experiences with two of them in a recent paper in the Annals of Thoracic Surgery; their work marks the first time the Melody has been used for mitral valve replacement.

As the child grows, the modified valve can be expanded by threading a thin balloon catheter into the heart, and carefully inflating it. “It’s much less invasive than open heart surgery, requires less recovery time,” says Emani. “By going this route, we could potentially leave the modified valve in place until a patient reaches adulthood, reducing the number of operations and the risk of lung swelling related to suboptimal valve function.

Sitaram Emani, MD, and Pedro del Nido, MD

“It opens up the opportunity to carry out mitral valve replacement in more children and at an earlier time point than has historically been possible,” he adds.

While the team doesn’t yet have long-term experience with the procedure, the initial outcomes look promising. “Two of our patients have already undergone their first growth-related valve dilations, and in both, the procedure went better than expected,” Emani says. “The others have gone almost a year without the need for additional surgeries, which is remarkable given the level of surgical care small children with mitral valve disease usually need.”

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