Valve-in-valve therapy – fracture mechanics of bioprosthetic heart valves

BALLOONS WILL BURST DEFECTIVE

ARTIFICIAL HEART VALVES

Replacing an artificial heart valve that no longer works will be safer for patients in the future. Researchers will gain knowledge about how to burst worn out implants to make room for new ones.

A defective valve is one of the most common heart diseases in the Western world. Every year, cardiac surgeons implant more than 300,000 artificial heart valves to recreate a normal blood flow pattern and thereby improve the pumping function of the heart in their patients.

Doctors can currently choose between a mechanical and a bioprosthetic implant. A mechanical heart valve is much more durable, but also has an increased risk of complications such as blood clots, and patients therefore need to take anti-coagulant drugs for the rest of their lives.

A bioprosthetic heart valve is made of animal tissue and therefore provides a more natural blood flow, where the risk of blood clots is minimal. The problem with these valves is that their durability is limited and they must therefore be replaced every fifteen to twenty-five years.

“Mechanical heart valves are typically offered to younger patients to avoid repeated surgical procedures. If it was possible to replace bioprosthetic heart valves without surgical intervention, however, it would provide doctors with more opportunities to use this type of implant,” says Associate Professor Peter Johansen.

In a new project collaboration between Aarhus University and Aarhus University Hospital, he will help establish evidence-based knowledge about how to replace defective heart valves safely and accurately.

Balloon technique may render surgical procedures unnecessary
For a number of years, Associate Professor Johansen has worked closely with clinical researchers at the Department of Cardiothoracic and Vascular Surgery, Aarhus University Hospital, where a gentle way to implant bioprosthetic heart valves via a catheter in the groin was originally invented and developed without the use of open heart surgery.

The same method is used in some cases as an alternative to repeating surgical procedures on patients with defective bioprosthetic heart valves, where the new valve is inserted in the old one. However, the space is sometimes so tight that it is first necessary to burst the existing and worn implant to make room for the new one.

“The doctors can insert a high-pressure balloon into the defective heart valve and pump it up to make a fracture line in the outer ring of the valve. This can make room for implanting a new valve via a catheter, thereby avoiding a new operation,” says Associate Professor Johansen.

The researchers will now use specially designed measuring equipment to very precisely determine how the doctors can burst the defective valve with a minimal risk of damaging the surrounding tissue.

Minimal risk of lesions of the aorta
This will take place in a considerable number of in vitro tests of different commercial heart valves that are systematically exposed to pressure in the laboratory. The combined measurements will contribute to clinical guidelines for how to burst different types of bioprosthetic heart valves in the most careful way.

“It’s relatively simple to burst a heart valve, but it requires meticulous studies if it’s to be done with precisely the pressure that’s required and no more. We’ll therefore – doctors and engineers together – gather new knowledge about carrying out this procedure so that patients are exposed to the least possible risk of lesions of the surrounding tissue,” says Associate Professor Johansen.

The researchers have designed an experimental set-up for this purpose, which consists of a manometer (pressure gauge), a high-speed camera and a CT scanner.

The camera can film up to 120,000 images per second and thereby photograph the movements in the heart valve structures when they burst. The CT scanner can look into the valves so to speak, which provides an opportunity to analyse the fracture in the ring surrounding the bioprosthetic valve.


PHOTO TOP: Specially designed measuring equipment very precisely determines how the doctors can burst a patient’s defective valve with a minimal risk of damaging the surrounding tissue. (Photo: Lars Kruse)