Around 1.35 million children worldwide are born with congenital heart disease each year. More than 24 percent of those children have heart valve defects. Although prosthetic heart valves can be fitted to replace the damaged ones, current devices are fixed in size and cannot expand without the loss of valve function.
As the child grows, this becomes a problem, and the valves have to be replaced every few years with larger versions via open-heart surgery. However, a new design created at Boston Children’s Hospital could curb the need for these highly invasive procedures.
The team led by Sophie Hofferberth, a surgical resident at Brigham and Women's Hospital, created an expandable valve that could allow children to keep the same one until adulthood. According to the study, published in Science Translational Medicine, only a minimally invasive balloon catheter procedure would be necessary to effectively expand the device, whilst allowing it to still retain its functionality.
Inspiration for the new design came from human venous valves located in the deep veins of the leg. Current prosthetic heart valves used for children have three leaflets (or flaps) that open and close to keep the blood flowing in the right direction, replicating our native outflow valves in the heart. However, venous valves only have two leaflets. In response to increased volumes of blood passing through the veins, this bileaflet geometry enables the valves to maintain a one-way flow even when the veins have expanded.
"Veins carry approximately 70 percent of our blood volume," Hofferberth explained in a statement. "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 prototype valve, made from two synthetic leaflets attached to a stainless steel stent, has undergone benchtop studies, computer simulations, and extensive testing in large animal models, namely sheep. Seven juvenile sheep were fitted with the valve, and at three points over a 10-week period successfully underwent balloon expansion to accommodate growth. The valves were also tested across a range of dimensions in various sized sheep and remained fully functional.
In the 10 week observations of the growing sheep, the researchers noticed another benefit of the valve compared to current designs. "A shortcoming of many existing devices is the presence of flow disruptions that lead to blood clot formation and early valve deterioration," said Hofferberth.
However, there was no evidence of blood clot formation in the sheep, even without them receiving blood-thinning medication, which recipients of prosthetic heart valves are currently given.
"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," Hofferberth concluded.
With such promising results, the team hope a clinical trial will be initiated within one to two years.
"If our preclinical results hold up in human testing, this could transform the field," Pedro J. del Nido, chairman of Cardiovascular Surgery at Boston Children's Hospital, whose lab was used for the study.