Scientists 'grow' replacement heart valves.

Using a patient's own heart muscle cells as seeds for new tissue, researchers are testing a novel technique to "grow" replacement heart valves for persons with cardiac disease.

Christopher K. Breuer, a physician at Children's Hospital in Boston, says the new method for engineering heart valve tissue could offer an alternative to animal-derived or mechanical devices.

"Tissue-engineered heart valves do not have many of the problems associated with today's replacement valves and may some day offer an improvement over today's state-of-the-art therapy," Breuer said last week at a meeting of the American Chemical Society in Anaheim, Calif.

In the United States, physicians replace approximately 60,000 heart valves each year, mostly with plastic prostheses or valves fashioned from the vascular tissue of pigs. Such valves cannot develop, grow, or repair themselves, and both kinds sometimes trigger immune responses leading to blood clots, infections, or rejection, Breuer says.

Artificial valves last only 10 to 20 years, creating problems not only for children who have heart operations, but also for adults who need new heart valves at age 40 and may have to face a second operation at age 50 or 60.

"These are difficult operations and you don't want to put someone through one more than once," Breuer says. In theory, the new living valve should integrate fully into the patient's heart tissue, growing and developing along with the person receiving it.

To engineer the valve, a physician removes a small piece of tissue from a patient's heart, then cultures the cells in a laboratory, separating them into the three cell types found in valves: smooth muscle, endothelial, and fibroblast.

Those cells are then implanted into a biodegradable material, polyglycolic acid, which surgeons already use in dissolvable sutures, Breuer says. The material serves as a scaffold, enabling the cells to form living valve tissue. After 6 weeks, the foreign material dissolves completely, leaving in its place a biological valve that resembles natural heart tissue.

Breuer says that he and his colleagues are "evaluating the biomechanical properties of these structures and comparing them to native heart valve tissue."

The research team estimates that many of the 2,300 patients who receive heart transplants every year could potentially benefit from this research, as could the 40,000 patients who need, but cannot get, replacement hearts, owing to a limited supply of donor organs.

So far, the researchers have tested the procedure in lambs, with good results, Breuer reports. However, the valves will require more research and development before any testing can begin in humans.