Scientists have created a heart valve replacement that can be expanded over time as the organ grows.

They say it is a big step towards a major goal in heart valve prosthetics.

In a new study the artificial valve safely worked in growing young lambs for a period of up to 10 weeks.

Researchers say that although studies with longer follow-up times are needed to further validate the design, the device could offer a superior alternative to traditional, fixed-diameter heart valve prostheses.

The nature of this means that children with congenital heart disease require repeated open-heart surgeries during childhood to replace the valve with a larger version.

However, scientists say the new device created at Boston Children’s Hospital could allow children to keep the same prosthetic valve until adulthood.

Published in Science Transitional Medicine, they suggest it could also benefit adults with heart valve defects.

More than 1.35 million children worldwide are born with a congenital heart disorder each year, resulting in an annual expense of around six billion US dollars.

Of these disorders, most that involve heart valves are treated with prosthetic replacements.

To provide a more permanent solution that reduces surgical burden, Sophie Hofferberth and colleagues created a heart valve that draws inspiration from valves in human veins, which can expand and contract to handle large changes in blood flow volume.

It is composed of two synthetic leaflets attached to a stent and can be manually expanded with a balloon catheter to accommodate larger volumes of blood moving through the heart.

When implanted into four lambs and four adult sheep, the prosthetic valves showed good performance without impeding blood flow.

A separate test in seven other lambs found the valves remained functional for 10 weeks without causing injury or major inflammation.

The scientists caution that longer-term animal studies should assess the valve’s durability and effects on the heart, as well as the structural integrity of the expandable leaflet design.

Dr Pedro del Nido, chairman of cardiovascular surgery at Boston Children’s Hospital and senior author on the paper, said: “We hope to bring this new device into clinical testing fairly rapidly.

“If our pre-clinical results hold up in human testing, this could transform the field.”

Dr Hofferberth said: “A shortcoming of many existing devices is the presence of flow disruptions that lead to blood clot formation and early valve deterioration.

“Our design achieves a favourable flow profile that seems to facilitate effective valve washout and minimise flow stagnation, which is likely to be an important determinant of long-term device durability.”

The team believes their data support initiation of a clinical study within one to two years.