Coronary research: Study may yield better heart valves

By Jim Barlow

Heart-valve surgery is a medical miracle that extends life, but mechanical valves require anticoagulants to prevent life-threatening blood clots, and tissue valves have shorter life spans. Enter the pig, which may boost the work of both heart researchers and valve manufacturers.

Scientists at the UI College of Veterinary Medicine began inserting prosthetic heart valves into young Yorkshire-cross pigs in late October in projects funded by industry and the National Institutes of Health.

Their goal is threefold:

• To prove that a pig's human-like heart and blood system can provide accurate information about the interaction among valves, blood and hearts without putting humans at risk;
  
  
• To reduce or eliminate the need for anticoagulants through design changes;
  
  
• To help manufacturers produce more durable valves. Mechanical valves last 15 to 20 years; tissue, or bioprosethetic valves, usually made with heart tissue from pigs, last seven to 10 years.

"Pigs are almost ideally suited for the work we do, because their cardiovascular systems and their blood are very similar to that of humans," said David Gross, director of the new UI Cardiovascular Research Laboratory and head of the department of veterinary biosciences. "Heart valves are normally tested in sheep or in calves, which are ruminants with very different coagulation schemes than in humans and in pigs. The results can be very misleading."

Gross argues the case for the use of pigs -- which, like humans, develop atherosclerosis in response to a high-fat diet -- as an animal model in cardiovascular research in an article accepted for publication in Europe's International Journal of Artificial Organs.

Gross and colleagues Mrinal K. Dewanjee and Shu Ming Wu initially are studying the onset of interaction of blood platelets and neutrophils, both of which are part of the body's defense response, with a valve. The platelets and neutrophils are labeled with radioisotope tags developed by Dewanjee, which allow the researchers to take nuclear images of the activity with a gamma camera.

"This technique will show us where the problem areas are -- where thrombi [blood clots] are formed," Gross said. "We'll be able to watch the thrombi over time to see how and why they form and where they go. We also want to identify the mechanisms involved in the degeneration and calcification that occurs in the tissue valves. This information will enable us to recommend design changes in the valves and in the sewing rings that are used to hold them in place."

The researchers will be inserting both mechanical and tissue valves into a total of 24 pigs by the end of January. For the more than 100,000 North Americans who receive replacement heart valves each year, the findings could lead to improved quality of life and greater longevity.

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