Prosthetic Heart Valve Prevents Coagulation

A prosthetic valve enables blood to swirl naturally as it flows, reducing stress on blood vessels.

by Jeff O'Heir
April 10, 2017

Prosthetic heart valves can prolong a person’s life by dozens of years. Follow-up treatment, though, usually involves a lifelong regimen of potentially dangerous anticoagulants. Alexander Gorodkov is hoping to fix that with a newly designed valve that allows blood to flow on its natural course.

Researchers have known for more than 20 years that blood flows through the left ventricle—the chamber of the heart that pumps blood to the body—in a swirling, tornado-like fashion. The motion helps to maintain healthy blood vessels by preventing unnecessary strain on their lining.

The majority of prosthetic valves, though, create an obstacle in the inner wall, or lumen, of the aorta, that causes blood to flow quickly in a linear fashion. This occurs because the faster blood flow increases mechanical stress on the lumen of the valve. That in turn triggers biochemical changes that activate blood coagulation.

Anticoagulation drugs can prevent this, but they can create another set of complications.

“As a result of such therapy, there are elevated risks of bleeding due to trauma, spontaneous intra-organ hemorrhages, bleeding of the gastrointestinal tract, and hemorrhagic stroke,” said Gorodkov, a specialist in fluid dynamics and chief of the experimental department at the Bakulev Research Center for Cardiovascular Surgery in Moscow. “The risk of these complications increases with prolonged use of drugs.”

´╗┐Mimicking the Heart Valve

As described in a paper published by ASME, in designing their new prosthesis, Gorodkov and his team set out to eliminate the need for anticoagulants by mimicking the natural valve’s ability to create tornado-like flow.

Although the researchers began designing the device 15 years ago, it took them until last year to find a manufacturer in Russia that could provide the precision machining needed to create the complex curved surfaces on the small parts of the valve, which is made from pyrolytic carbon, a long-lasting material used to make many of today’s prosthetic valves.

“This allows us to continue the preclinical trials and start clinical trials,” Gorodkov said.

When designing its valve, which they dubbed the “tornado-compatible valve,” the team made sure that its inner walls were free from any kind of obstacle that could disrupt the natural swirling flow. Three cusps, or leaflets, are attached to the outer ring with rotary joints. When the cusps are open, the inside of the valve remains circular.

But when the cusps are partially closed, they enable the blood to swirl like a tornado as it flows. That’s because the reverse side of each cusp is curved to mimic the aortic sinus, the widening of the ascending aorta located just above the cusp of the natural valve. 

Learning from Clinical Trials

The team implanted its prosthetic valve in a pig for 10 months. Anticoagulant drugs were used for the first month but no drugs were used for the remaining nine. The pig tripled its weight, however, and developed aortic stenosis, in which the aortic valve becomes too tight and doesn’t open properly, which in humans can lead to chest pain, breathlessness, and reduced activity level.

The researchers determined that the device did not fit the pig, and the Bakulev Center’s ethical committee determined that it was safe enough to try experimentally in humans. The researchers implanted it in a 48-year-old man with aortic stenosis, who returned to his job after three months and is doing fine a year later, though he remains on anticoagulant therapy.

Gorodkov is now working on ways to reduce the cost of the valves. The researchers have to complete a roughly two-year cycle of preclinical and clinical trials and obtain regulatory approval in Russia to commercialize the product there. They eventually plan to release it to the European and U.S. markets.

 

Jeff O’Heir is a science and technology writer based in Huntington, New York.