What are Artificial Heart Valves ?
Artificial Heart Valves
Who needs artificial heart valves?
The 4 heart valves work continuously to keep blood flowing to the lungs and to the body. Sometimes, disease may damage the heart valves so that they function poorly or stop working completely. This may cause reduced ability to exercise or work, heart failure, or death. When damaged valves can no longer be repaired, artificial valves are used to prolong and greatly improve the quality of life.
What is required of an artificial heart valve?
The requirements for an artificial heart valve are staggering. The valve must be easy to insert. It must last a long time. It must be able to open and close 35 million times a year for 20 to 50 years. It must allow high blood flow with minimal turbulence and must not leak. The valve also should not cause blood clots.
What kinds of artificial heart valves have been developed?
Today’s artificial heart valves fall into 3 categories: caged-ball valves, single-leaflet (tilting disk) valves, and bileaflet valves. Today, most surgeons use leaflet valves for replacement. All 3 require the long-term use of blood-thinning drugs (anticoagulants) to reduce the risk of blood clots.
Caged-ball valves were among the first to be used. They are made of a stainless steel cage that traps an enclosed, floating ball. The hollow ball is made from titanium or pyrolytic carbon, both of which are lightweight. The whole valve is big, and blood flow through it is turbulent. The struts of the cage may cause small blood clots to form that can cause trouble if carried into the bloodstream.
Single-leaflet (tilting disk) valves are those in which a thin plastic wafer pivots into open and closed positions. The blood flow patterns for these valves are better than the caged-ball type, but the valves still cause blood clots.
The bileaflet valve consists of 2 hinged leaflets made of very light pyrolytic carbon, and has a very low failure rate. The flow characteristics of bileaflet valves are excellent and blood clotting seems to be slightly less of a problem than with caged-ball and disc valves.
Three other types of valves are available. These are not strictly artificial: one comes from a pig (porcine valve), one from human organ donor hearts, and one is made from organ donor pericardium. (The pericardium is a strong tissue sac inside which the living heart beats.) All types must be specially treated to avoid rejection by the recipient’s body. An advantage of the pig valve is that it is available in several sizes and is plentiful. All valves have the advantage of not requiring the long-term use of blood thinners. All have the disadvantage of being less durable than mechanical valves after 10 years of use. They probably work best in elderly patients.
No artificial valve is perfect. However, they offer a second chance for many people with diseased heart valves.