Cardiovascular Procedures - Tissue Versus Metal Valves: Weighing The Factors

Author:

College of Physicians and Surgeons, Columbia University

Medically Reviewed On: September 22, 2004

Bioprosthetic Valves
Bioprosthetic valves are made from biological tissues, mostly from valves of pigs. After preserving the valve in a special preservative called glutaraldehyde, the tissue strength is increased and the chance of the patient's immune system rejecting this foreign material is diminished. These processed biological valves are then mounted on a stent (splint left inside body to help healing process) for implantation. There are other tissue valves as well and we will discuss them later on.

The benefits
Tissue valves have low risk of clot formation. The incidence of clot formation associated with tissue valves is no different from patients with mechanical valves taking adequate blood thinning medication. Therefore, most patients with tissue valves do not need to be on blood thinners. This is the major advantage of tissue valves. Blood thinner-related bleeding complications are much less frequent in patients with tissue valves than patients with mechanical valves.

The drawbacks
On the other hand, tissue valves have limited life spans. They don't last forever and if you have a tissue valve, you will need another operation in the future, especially if you are young. The main cause of valve tissue degeneration is calcium deposition with resultant hardening of the tissue known as calcification. This degenerative process increases with time. The failure rate at 3 years after implantation is miniscule, but increases to 5 to 10 percent at 6 to 7 years and reaching 30 percent by 10 years. In children and adults under 35 years of age, tissue degeneration is even faster. The reason for this marked increase in failure rate is not entirely clear. Nevertheless, the failure rate of tissue valves implanted in patients under 35 years old is about 45 percent at 10 years after the initial operation. The process of tissue degeneration tends to be gradual, which allows for early detection and monitoring, as well as re-operation for valve replacement when it becomes necessary.

Other tissue valves available
There are other tissue valves available today. Of course, the best valve is your own valve. Valve repair, rather than valve replacement, should be done whenever possible. One of the most popular tissue valves today is made from bovine pericardium - the lining of the sac around the heart of a cow. These bovine pericardial heart valves seem to last longer than porcine (pig) artificial heart valves. A human heart valve is also available. It is called a cryopreserved human heart valve and does not require blood thinner and has a long life span.