What is a heart valve replacement?
Valve replacement surgery is a procedure used when a heart valve no longer functions properly. There are several reasons that a heart valve may fail. Sometimes, a major defect present at birth must be repaired immediately. Minor defects present at birth may go undetected for years. When and if these minor defects become worse as a result of aging, valve replacement surgery may be necessary. Another cause of heart valve damage is infection. Rheumatic fever can cause the scarring of a valve. These scars can become more of a problem with age, and surgery may eventually be necessary. Bacterial endocarditis is another type of infection that can damage the heart very quickly. Valve replacement surgery is often needed as a result of this type of infection.
When a heart valve is damaged, the result is usually stenosis or regurgitation. Stenosis occurs when the valve becomes thick and hard. As a result, normal blood flow through the valve is obstructed. A valve that becomes stretched or weak may not close properly, resulting in blood flowing backward through the valve; this is called regurgitation. When the blood flows through an abnormal valve, turbulence occurs and a sound is made. This sound, called a murmur, generally can be heard with a stethoscope.
When a heart valve fails to function properly, the ability of the heart to do work is impaired. In an attempt to maintain normal work levels, the heart begins to enlarge, or experience hypertrophy . When further hypertrophy is no longer possible, the heart fails. This condition will result in permanent damage to the heart muscle and eventually death. Some of the symptoms of valve problems include chest pain or tightness, shortness of breath, temporary blindness, slurred speech, weakness, numbness, lack of coordination, unusually rapid weight gain, fatigue, and loss of consciousness. These symptoms are typically the result of inadequate blood flow, particularly to the brain.
In some cases, surgery can be used to repair the valve. Many times, however, the damage is too extensive for this type of surgery, and the valve must be replaced. The replacement valve may come from a deceased person’s heart or from an animal’s heart (usually that of a pig), or it may be a mechanical (prosthetic) valve. Prosthetic valves are made from metal, plastic, or carbon ceramic.
During valve replacement surgery, the chest is opened to expose the heart. Blood flow through the heart is diverted through an oxygenator and a pump that maintains the flow of oxygenated blood throughout the body. The surgeon removes the damaged valve and sutures a replacement valve to the heart. Upon completion of the surgery, if the replaced valve functions effectively, normal blood flow is restored through the heart.
Heart valve replacement is a very reliable procedure. Although problems with the new valve are possible, the majority of these surgeries are quite effective. Nevertheless, there are two long-term concerns for the patient. Blood thinners or anticoagulants—drugs that slow the clotting process and may prevent blood clots—are usually required with prosthetic valves. These drugs help prevent blood from coagulating in and around the new valve. Some patients must also take antibiotics to prevent additional infections in the heart. Antibiotics are needed especially when patients visit the dentist, when bleeding is likely. If bleeding occurs, bacteria may enter the blood and become lodged in the replacement valve. The ensuing infection can cause further damage to the heart.
When one compares the use of tissue versus mechanical (prosthetic) valves for replacement, some differences emerge. In general, tissue valves work better. In addition, they are less likely to require drugs to increase blood-clotting time. On the other hand, they are harder to obtain. With more people acting as donors and with better preservation techniques becoming available, tissue replacements are preferred.
Mechanical valves were first used as replacements for damaged valves in the early 1960s. In 1962, the initial clinical use of tissue valves was described. Tissue valve replacements were conducted simultaneously by Donald Ross in England and Sir Brian Barratt-Boyes in New Zealand. The acceptance of tissue valve use was slow because the number of donors was small and the methods for preserving valves for later use were poor. The result was shorter survival times for the replacement valves used in the 1960s and early 1970s.
By the 1980s, better preservation techniques were developed, which allowed surgeons to use living human tissue. These replacements have been found to be superior to nonliving tissues and mechanical valves. In the future, both mechanical and tissue replacements will continue to be used, based on availability and the specific needs of the patient. Newer, less invasive surgical approaches are being investigated in clinical trials.
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