Mending a broken heart valve

21 February 2020

HEARTVALVE.jpg

a diagram of heart and valve

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An expandable heart valve - that could spare millions from multiple hazardous heart surgeries - has been invented by US researchers...

The human heart contains four heart valves that control the flow of blood, ensuring blood flows only in one direction. Each year around the world, however, over a million children are born with heart diseases. An estimated 25% of these are related to heart valve defects.

These children are often treated using prosthetic valves. But, as the children grow, so does the heart, so the prosthetic valve needs to be replaced, necessitating multiple open heart surgeries. 

Children requiring their first surgery before they turn two years old, typically require four more surgeries before they reach adulthood.

Open heart surgery is not risk free: the mortality rate is between 2 and 30%, and the process also places stress and worry on the family and patient.

The new expandable heart valve avoids the need for repeat surgeries, requiring an operation only once: the first time the valve is inserted.

Sophie Hofferberth, who is based at Boston Children's Hospital and developed the valve, was inspired by the shapes of the valves in our veins. These change shape dramatically as our body moves but the valves maintain their function. So she and her team set out to copy this geometrical profile and design an artificial valve with the same two “leaflets”.

To make the biomimetic leaflets in the valve grow, they used a technique called “balloon expansion”. This involves inserting a wire through a small incision, typically near the top of the leg, and threading a wire through to the heart valve. The small balloon attached at the tip of the wire is temporarily inflated to stretch the valve to the right dimensions.

This new valve can also help many children who do not have access to any treatment when there is not a heart valve small enough for them, as the minimum size currently available is 15mm.

Once the mechanics of the valve expansion were tested in the lab, the valve was trialled in sheep and lambs.

Sheep are regarded as the gold standard for open heart models, as their heart anatomy is the most similar to humans. The mechanisms of valve failure in sheep is faster than in humans, which also makes it a good predictor for the success or failure of an artifical heart valve. 

The results in the sheep trial were very promising. Taking images of the sheep's blood vessels and sound waves of the sheep's hearts showed that 6/7 sheep took the prosthetic valve well, and only one of them had mild regurgitation issues.

The researchers will now conduct some longer term tests on animals, but also make sure the valve works in every condition by testing it through millions of cycles of valve shapes in the lab. But if everything goes right, the first human trials should be in 18 months time!

This is all the more likely as the team managed to develop a heart valve using off-the-shelf materials, which work across a range of sizes.

As Hofferberth points outs, children born in five years’ time with heart valve defects will soon be able to “grow up and have a more active and healthy life, and not so have so many open heart surgeries in their lifetime, because they will have replacement valve that can grow with them all the way to adulthood.”

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