heart valve replacement
Heart Valve Replacement
Heart valve replacement is a surgical procedure during which surgeons remove a damaged valve from the heart and substitute a healthy one.
Four valves direct blood to and from the body through the heart: the aortic valve, the pulmonic valve, the tricuspid valve, and the mitral valve. Any of these valves may malfunction because of a birth defect, infection, disease, or trauma. When the mal-function is so severe that it interferes with blood flow, an individual will have heart palpitations, fainting spells, and/or difficulty breathing. These symptoms will progressively worsen and cause death unless the damaged valve is replaced surgically.
Abnormal tricuspid valves usually are not replaced because they do not cause serious symptoms. Mildly or even moderately diseased mitral valves may not need to be replaced because their symptoms are tolerable or they can be treated with such drugs as beta blockers or calcium antagonists, which slow the heart rate. However, a severely diseased mitral valve should be repaired or replaced unless the person is too ill to tolerate the operation because of another condition or illness.
After cutting through and separating the breast-bone and ribs, surgeons place the patient on a cardiopulmonary bypass machine, which will perform the functions of the heart and lungs during the operation. They then open the heart and locate the faulty valve. Slicing around the edges of the valve, they loosen it from the tendons that connect it to the rest of the heart and withdraw it. The new valve is inserted and sutured into place. The patient is then taken off the bypass machine and the chest is closed. The surgery takes three to five hours and is covered by most insurance plans.
There are three types of replacement valves. One class is made from animal tissue, usually a pig's aortic valve. Another is mechanical and is made of metal and plastic. The third, includes human valves that have been removed from an organ donor or that, rarely, are the patient's own pulmonic valve.
There is no single ideal replacement valve. The choice between an animal valve or a mechanical valve depends largely on the age of the patient. Because valves obtained from animals have a life expectancy of 7-15 years, they usually are given to older patients. Mechanical valves are used in younger patients because they are more durable. Because mechanical valves are made of foreign material, however, blood clots can form on their surface. Therefore, patients who receive these valves must take anticoagulants the rest of their lives.
Donor or pulmonic valves are given only to those patients who will deteriorate rapidly because of a narrowing of the passageway between the aorta and the left ventrical (aortic stenosis). These valves are limited in their use because of the small supply available from donors and the strain that could be caused by removing and transferring a patient's own pulmonic valve.
Before patients undergo heart valve replacement, they must be evaluated carefully for any signs that they may not tolerate the surgery.
Preoperative tests include:
- electrocardiography, which assesses the electrical activity of the heart
- echocardiography, which uses sound waves to show the extent of the obstruction of blood flow through the heart and determine the degree of loss of heart function due to the malfunctioning valve
- chest x ray, which provides an overall view of the anatomy of the heart and the lungs
Cardiac catheterization may also be performed to further asses the valve and to determine if coronary bypass surgery should also be done.
A patient usually spends one to three days in the hospital intensive care unit (ICU) after heart valve replacement so that the working of his or her heart and circulation can be monitored closely. When first brought to the ICU after surgery, the patient undergoes a neurological examination to be sure he or she has not suffered a stroke. The patient continues to breathe by means of a tube inserted in the trachea at the time of surgery. This mechanical ventilation is not withdrawn until the patient is fully awake from anesthesia, shows signs that he or she can breathe satisfactorily without mechanical support, and has steadfast circulation.
Once stablilized, the patient is transferred to a standard medical/surgical unit where he or she receives drugs that will prevent excess fluid from building up around the heart. As soon as possible, the patient begins walking and exercising to regain strength. He or she is also placed on a diet that is low in salt and cholesterol.
After being released from the hospital, the patient continues a daily exercise program that includes vigorous walking, and he or she may also join a recommended cardiac rehabilitation program. He or she usually can return to work or other normal activities within two months of the surgery.
Complications following heart valve replacement are not common, but can be serious. All valves made from animal tissue will develop calcium deposits over time. If these deposits hamper the function of the valve, it must be replaced. Valves may become dislodged. Blood clots may form on the surface of the substitute valve, break off into the general circulation, and become wedged in an artery supplying blood to the brain, kidneys, or legs. These blood clots may cause fainting spells, stroke, kidney failure, or loss of circulation to the legs. These blood clots can be treated with drugs or surgery.
Infection of heart muscle affects up to 2% of patients who have heart valve replacement. Such an infection is treated with intravenous antibiotics. If the infection persists, the new valve may have to be replaced.
Anticoagulants — Drugs that prevent blood clots from forming.
Aortic valve — A fold in the channel leading from the aorta to the left ventricle of the heart. The aortic valve directs blood flow that has received oxygen from the lungs to the aorta which transmits blood to the rest of the body.
Cardiac catheterization — A thin tube called a catheter is inserted into an artery or vein in the leg, groin or arm. The catheter tube is carefully threaded into the area of the heart needing surgical repair. A local anaesthesia is used at the insertion sites.
Cardiopulmonary bypass machine — A mechanical instrument that takes over the circulation of the body while heart surgery is taking place.
Echocardiography — A diagnostic instrument that assesses the structure of the heart using sound waves.
Electrocardiography — A diagnostic instrument that evaluates the function of the heart by measuring the electrical activity generated by the beating of the heart.
Mitral valve — A fold in between the left atrium and the left ventricle of the heart that directs blood that has received oxygen from the lungs to the aortic valve and the aorta.
Pulmonic valve — A fold in the pulmonary artery that directs blood to the lungs. It may be transferred to replace a severely diseased aortic valve during heart valve replacement surgery for aortic stenosis.
Tricuspid valve — A fold in between the right atrium and the right ventricle of the heart that directs blood that needs oxygen to the lungs.
Few patients die as a result of the surgery. Approximately 3% of all patients die during or immediately after heart valve replacement, and less than 1% of patients below the age of 65 die because of the operation. The vast majority of patients who have heart valve replacement return to normal activity after the surgery. Depending on the type of valve they receive, these patients will have no symptoms of valve abnormality for at least seven years. Also, their quality of life will improve because they may no longer have difficulty breathing, fainting spells, or palpitations.
American Heart Association. American HeartAssociation's Your Heart: An Owner's Manual. Englewood Cliffs, NJ: Prentice Hall, 1991.
The American College of Cardiology. 9111 Old Georgetown Road, Bethesda, MD 20814. (800) 253-4636. http://www.acc.org.
American College of Surgeons. 55 E. Erie St., Chicago, IL 60611. (312) 202-5000. http://www.facs.org.
American Heart Association. 7320 Greenville Ave. Dallas, TX 75231. (214) 373-6300. http://www.americanheart.org.
Gale Encyclopedia of Medicine. Copyright 2008 The Gale Group, Inc. All rights reserved.
heart valve replacementA method of treating the effects of a leaking or narrowed heart valve by removing it and substituting a donated human valve, a pig heart valve or a mechanical prosthesis.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005