For some children born with congenital heart disease, prosthetic valves that maintain a healthy flow of blood are a harsh reality of their young lives. This not only requires open heart surgery to implant the device initially, but repeated high-risk procedures to replace them every few years as their body grows. Researchers at Boston Children’s Hospital have been working towards more of a one-size-fits all solution, and have come up with a design they say works at a variety of diameters, and can be adjusted as needed without the need for invasive surgeries down the track.
Around nine in 1,000 babies are born with congenital heart defects, according to the American Heart Association, making them the most common form of birth defect. This can mean abnormalities in the walls of the heart, the neighboring arteries and veins, or the valves that regulate the flow of blood in and out of the organ.
When a child is born with a heart valve defect, surgeons can implant prosthetic heart valves to restore the organ to healthy function, but these have a fixed diameter, which means they need replacing at regular intervals. According to Boston Children's Hospital, those who receive prosthetic valves before age two will require at least five open-heart surgeries to replace them before they reach adulthood.
The prosthetic valves used today feature a set of three flaps that work together to control blood flow in either direction. In search of a better way forward, the researchers looked to the valves found in the deep veins of our legs, which feature just two flaps and are able to maintain flow even as the veins expand in response to heavier volumes of blood.
"Veins carry approximately 70 percent of our blood volume," says Sophie C. Hofferberth, who led the research. "The vein dimensions can change dramatically depending on body position, yet the valves must remain functional. We mimicked the geometric profile of the human venous valve to design a bileaflet valve of programmed dimensions that is adaptable to growth without loss of one-way flow control."
The team evaluated this valve in lab tests and on animal models, where it proved fully functional when expanded to a wide range of dimensions, successfully accommodating different pressures and flow rates. In a human patient, the scientists believe the prosthetic could be expanded as needed with a balloon catheter approach, which they describe as minimally invasive.
In addition to a constant, healthy flow, the experiments also demonstrated that the prosthetic valve could minimize the risk of blood clots. Tested in a growing sheep model, the team observed no signs of blood clotting over a 10-week period, without the use of blood thinning drugs usually given to recipients of traditional prosthetic valves.
"A shortcoming of many existing devices is the presence of flow disruptions that lead to blood clot formation and early valve deterioration," says Hofferberth. "Our design achieves a favorable flow profile that seems to facilitate effective valve washout and minimize flow stagnation, which is likely to be an important determinant of long-term device durability."
With these exciting early results, the team is now setting its sights on human trials, which could begin within one or two years.
"We hope to bring this new device into clinical testing fairly rapidly," says Pedro J. del Nido, MD, Chairman of Cardiovascular Surgery at Boston Children's Hospital. "If our preclinical results hold up in human testing, this could transform the field."
The research was published in the journal Science Translational Medicine.
Source: Boston Children's Hospital via EurekAlert
