Sometimes a natural heart valve that is not working properly needs to be replaced surgically with a prosthetic valve. A prosthetic valve is a synthetic or tissue substitute for the natural valve. It is designed to mimic the natural valve's normal opening and closing motions. A prosthetic valve can replace any of the three heart valves – aortic, pulmonary or tricuspid. Prosthetic heart valves are divided into two basic categories: synthetic mechanical valves and biological valves made of human or animal tissue.
Several different forms of mechanical valves have been approved by the U.S. Food and Drug Administration (FDA) for use in hospitals in the United States. The different types vary in the mechanisms they use to open and close the valves.
In general, mechanical valves tend to last longer than biological valves, but they also carry a greater long-term risk of thromboembolism, which is a floating blood clot that can travel through the circulation, causing stroke and other problems. To help prevent thromboembolism, people who receive mechanical heart valves must take anticoagulant medications (anticlotting drugs) for the rest of their lives. However, this long-term use of anticoagulants also increases the risk of bleeding problems.
Although mechanical valves generally are used in younger patients because of their durability, the need for anticoagulant medication can complicate a pregnancy in young women.
Biological valves can be made of either human or animal tissue. Options include:
Autograft valves – In this case, the replacement valve is made from another valve within the patient's own heart. For example, the patient's pulmonary valve may be removed and used to fix the aortic valve. The missing pulmonary valve is then replaced by one of the other options.
Homograft valves – This replacement valve is taken from a deceased human donor.
Heterograft valves – In this case, the replacement valve comes from an animal donor, either a pig or a cow.
In general, biological valves are less durable than mechanical valves. They are more likely to wear out and need to be replaced. Because they are more likely to wear out, biological valves are used more often in people aged 65 to 70 or older because their expected lifespan is shorter. Since the long-term risk of thromboembolism is lower for biological valves than for mechanical valves, the patient doesn't normally need to take anticoagulants for more than three months after surgery. Therefore, many younger patients who have active lifestyles and do not want to take anticoagulants choose to use biological valves.
Currently, 71,000 to 79,000 heart valve replacements are done each year in the United States.