Growth-accommodating implants could repair heart valve defects

A novel implant under development holds promise to provide a better way to repair leaking heart valves in children. Designed by a team of researchers at Boston Children’s Hospital, Boston, Massachusetts, the implant incorporates a critical function that until now has not been featured in implants for children-accommodating growth.

“The implant is designed to correct anatomic deformities at the time of surgical implantation, but then gradually elongate to accommodate a child’s native growth,” says Eric N Feins, MD, one of 2 lead authors (along with Yuhan Lee) of the report on the implantable device for pediatric applications,¹ and currently a fellow in cardiothoracic surgery at Massachusetts General Hospital, Boston.

The implant is intended to be used as a growing annuloplasty ring. “A critical part of heart valve repair is to support the ring or annulus of the valve to prevent dilation, which often is a major cause of valve leak,” says Pedro J del Nido, MD, William E Ladd Professor and chairman, Department of Cardiac Surgery, Boston Children’s Hospital, one of 2 senior authors of the study (along with Jeffrey M Karp).

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In adults, inserting an annuloplasty ring made of polyester (a nongrowing prosthetic material) is done routinely to repair a heart valve. Implanting such nongrowing rings in children is not optimal because it would require additional operations as the child grows to implant larger rings, according to del Nido.

To date, no annuloplasty rings are available that accommodate the growth in children, and therefore the success rate of valve repair in children remains far lower than adults. “This is one of the first devices for the heart that is not only designed for children but also designed to accommodate the growth of the child, thus potentially improving the success rate of the valve repair procedure, and reduce the need for reoperations,” del Nido says.

How does it work?

The implant is mainly comprised of 2 parts, an outer braided sleeve and an inner biodegradable core. “The inner core defines the diameter of the outer sleeve, such that change in core diameter effects change in sleeve diameter and length,” says Feins. “As a result, core degradation is coupled to overall device length.”

Following surgical implantation, the core begins to degrade and allows the outer braided sleeve to elongate in response to the forces of the growing tissue on which it has been implanted, Feins explains. “The novelty of our device concept is that it employs a permanent braided sleeve that can provide ongoing structural support of the tissue, but it also has the ability to elongate as the degradable component goes away,” he says.

Testing the implants in ex vivo experiments using harvested swine hearts and in vivo experiments with both small and large animal studies, the researchers found no evidence of device fatigue. Importantly, the tests demonstrated an association between device core degradation and growth accommodation by showing normal heart valve growth in the presence of polymer core degradation, whereas the absence of core degradation was linked to significant growth restriction.¹

Given these promising results in animal studies, the researchers are now working with a biomedical device company to begin testing the technology for use in humans by further developing the implant for use in pediatric heart valve repair.

Other uses

Although the original design concept of the implant was conceived to address heart valve repair in children, Feins emphasizes that the design concept has important potential applications in other clinical areas such as orthopedics, where it could be applied to repair long-bone deformities and scoliosis in children.

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To date, surgical implants to repair these anatomic deformities in children are limited given their fixed size, which often results in additional operations to revise or remove the implants as the child grows.

REFERENCE

1. Feins EN, Lee Y, O’Cearbhaill ED, et al. A growth-accommodating implant for paediatric applications. Nat Biomed Eng. 2017;1:818-825.