"Using this tissue-engineered valve overcomes many of the problems with mechanical or donor valves because it is a living structure from the patient's own tissue, and so it does not cause an immunological reaction," said Pascal M. Dohmen, M.D., head of tissue engineering research and staff surgeon of the department of cardiovascular surgery at Charité Hospital in Berlin, Germany.
Dohmen and colleagues presented data on the first 23 patients to receive tissue-engineered pulmonary valves in the heart.
The patients, whose average age was 44, had aortic valve disease. The aortic valve connects the heart's left ventricle with the aorta, the main artery that distributes blood throughout the body. A diseased valve may either open or close improperly, and pressure can build in the ventricle, injuring the heart.
Doctors can treat the condition with drugs or by surgically replacing the patient's aortic valve with a donor valve, a mechanical valve or the patient's pulmonary valve. The pulmonary valve is between the right ventricle and the pulmonary artery. In a surgical "swap" called the Ross procedure, the abnormal aortic valve is replaced with the pulmonary valve, and the pulmonary valve is replaced with a donor valve.
Dohmen and colleagues engineered a new pulmonary valve from the patients' own cells. They implanted the patients' healthy pulmonary valve into the aortic position. Then they implanted the tissue-engineered valve in the right ventricular outflow tract, where the pulmonary valve originally was.
With up to three years of follow-up, the engineered valve's performance was "excellent," Dohmen reported. Echocardiography showed that the valves were functioning normally; the valve leaflets or flaps appeared smooth and pliable and showed no signs of calcification.
The patients were discharged from the hospital earlier, and were in better condition than other patients. They had no post-operative fever, which is often found in patients receiving donor heart valves, Dohmen said. Furthermore, the recovery time was shorter.
To engineer the new valve leaflets, the investigators extracted a small portion of vein from the patients' leg or arm. Then they grew endothelial cells from the vein on a donor valve scaffold in the laboratory. The scaffold had been stripped of cells, leaving only an elastin and collagen matrix for binding the patients' cells.
"In animal studies, we have seen that this matrix or scaffold will be absorbed by the body," Dohmen said. "In the mean time, the patient's cells will form a new scaffold. After about a year, the matrix is of the patients' own material.
"The problem until now was to reconstruct the right ventricular outflow tract," he said. "You cannot do this with regular animal (pig) or human donor valves because they will calcify early or degenerate soon after implantation, especially in patients under the age of 60."
Dohmen limits the use of the tissue-engineered valves to adults up to 60 years of age, but plans to explore the growth potential of the valves, with the hope of using them in children with congenital heart disease.
The heart valve scaffold technique is still considered experimental, he said.
Co-authors are Simon Dushe, Alexander Lembcke, Dietmar Kivelitz, Holger Hotz and Wolfgang F. Konertz.