Cardiac Valve Surgery
Cardiac valve surgery
Cardiac valve surgery is the repair or replacement of any of the four heart valves.
The heart consists of two upper chambers (right and left atria), two lower chambers (right and left ventricles), and four valves (tricuspid, pulmonary, mitral, and aortic) that keep blood flowing in only one direction. Blood coming from the body enters the right atrium and then passes through the tricuspid valve into the right ventricle. The right ventricle pumps the blood through the pulmonary valve into the pulmonary artery, which carries it to the lungs. In the lungs, the blood releases carbon dioxide (a waste produce of cellular metabolism) and picks up oxygen. The pulmonary vein returns the oxygen-rich blood to the left atrium of the heart. The blood passes through the mitral valve into the left ventricle. The left ventricle is the largest and most muscular chamber of the heart. When the left ventricle contracts, blood is forcefully pumped through the aortic valve and into the aorta. The aorta is the largest artery. It distributes this oxygen-rich blood to the rest of the body.
Heart valves are made up of two or three tissue flaps called leaflets. These leaflets open and close with the contraction and relaxation of the heart. The lubdub sound that the heart makes is the sound of the valves opening and closing. Abnormal heart sounds (heart murmurs) are often an early sign of valve problems.
Heart valves can fail in two ways. They can become narrowed (a condition called stenosis) so that not enough blood flows through the valve. This forces the heart to work harder. Stenosis occurs because of congenital (present at birth) heart defects, loss of flexibility and scarring of the leaflets, or valve damage caused by disease, most often rheumatic fever. Damaged valves can also fail to close completely, so that blood flows back into the chamber that has just been emptied. This condition is called regurgitation, and it also forces the heart to work harder. People with defective heart valves can develop chest pain (angina ), shortness of breath, dizziness , fainting , or heart arrhythmias , and congestive heart failure .
The purpose of cardiac valve surgery is to repair, when possible, any damaged to the valve so that blood flows smoothly in only one direction. When repair is impossible, as it often is, surgery is done to replace the entire valve and restore the patient to health.
Pregnant women who need cardiac valve surgery present special problems. For them, replacement of a defective valve with a tissue valve is often preferred to replacement with a mechanical valve. The only alternatives to cardiac valve repair or replacement are watchful waiting and medications to help relieve symptoms; often this approach is inadequate. Without repair or replacement surgery, the chance of sudden death in the short term increases substantially. The operating team will take into consideration the patient's general health, effectiveness of medications, and age when recommending cardiac valve surgery and explain the risks and benefits to the patient.
Cardiac valve repair and replacement often requires open-heart surgery. Sometimes, especially with repair procedures, minimally invasive surgery can be performed in which a smaller opening in the chest is made and the breastbone (sternum) is not broken. This reduces blood loss and the chance of infection and speeds recovery. Aside from these benefits, a minimally invasive valve repair/replacement is not radically different from an open-heart procedure. About 95% of valve surgeries are performed on either the mitral or aortic valves.
The patient receives general anesthesia . The cardiothoracic surgeon makes a cut in the chest along the sternum and then breaks the sternum to have access to the chest cavity. The patient is connected to a heart-lung machine. This piece of equipment provides cardiopulmonary bypass and mechanically provides circulation and respiration so that the heart can be stopped and repair/replacement surgery can occur.
Once the patient is stable on the heart-lung machine, the surgeon makes an incision in the heart to reveal the defective valve. The surgeon then decides if the valve can be repaired or if it must be replaced. Common repairs include separating fused leaflets to widen the opening of the valve (a commissurotomy), removing calcium deposits from the valve to improve flexibility (decalcification), removing a defective or floppy section of a leaflet, then sewing the remaining valve leaflets back together (resection), repairing holes or tears in valve leaflets, and sewing synthetic material into the stem of the valve to provide additional support.
When the valve cannot be repaired, the entire valve is replaced. Replacement valves can be either mechanical or biological. Mechanical valves are made of metal and treated carbon. They have the advantage of longevity and rarely need replacement during the patient's lifetime. Their main disadvantage is that patients must take anticoagulant (blood-thinning) drugs such as warfarin (Coumadin) for the rest of their lives to prevent blood clots from forming in the valve. Anticoagulant drugs can have serious side effects and must be kept within a tightly regulated range. Mechanical valves also make a clicking sound as they close that some patients can hear and find annoying.
Biologic or tissue valves come from pigs (porcine valves), cows (bovine valves), or human cadaver donors (homografts or allografts). Human valves are in very short supply. All tissue valves are treated chemically so that the patient's immune system will not reject them. The main advantage of tissue valves is that the patient only needs to take anticoagulation drugs for a few months after the surgery. The main disadvantage is that tissue valves tend to wear out and often need replacement in 7–12 years. The age and health of the patient usually determine the type of valve used.
The valve is sewn into place, the breastbone is pulled together with wire twists, a drain is inserted in the chest, and the chest opening is closed. The patient is removed from the heart-lung machine when breathing and heart function are stable. The patient will be closely monitored in an intensive care unit (ICU) for several days.
Before cardiac valve surgery, the patient will undergo a series of diagnostic cardiac tests to give the surgeon as much information as possible about the valve defect. These tests include:
- electrocardiogram. This noninvasive test records the electrical activity of the heart and is useful is assessing general heart health. It may indicate that the heart wall is thickened.
- chest x-ray. A chest x-ray may show an enlarged heart or calcium deposits in the valve leaflets.
- electrocardiogram. This noninvasive test uses ultrasound waves to visualize soft tissue structures in the chest. Special Doppler electrocardiograms can track the flow of blood through the heart and show whether valves are leaking. A transesophageal echocardiogram, in which a tiny device that emits the sound waves is threaded down the throat while the patient is sedated, may be necessary to obtain a clear picture of certain valves.
- cardiac catheterization. An invasive test done under anesthesia in which a catheter (tiny tube) is inserted in a blood vessel at some distance from the heart (often in the elbow or groin) and threaded through the circulatory system into the heart where it measures blood flow and blood pressure on either side of the valve. Often during cardiac catheterization, a dye is injected into the bloodstream so that the cardiologist can assess the health of the coronary arteries (arteries that supply blood to the heart).
QUESTIONS TO ASK YOUR DOCTOR
- In your opinion, can my defective valve be repaired or must it be replaced?
- Am I a candidate for a minimally invasive procedure?
- If my valve needs replacing, what type of valve will I receive and why do you think that type is best for me?
- How many valve surgeries have you done in the past three years?
- How many valve surgeries are done at this hospital annually?
- Can you tell me about the type of cardiac rehabilitation I will need after surgery?
- Can you refer me to social services that may help me and my care givers during my recovery?
In addition to these tests, the patient will undergo standard pre-operative blood and urine screening and will meet with the anesthesiologist to discuss medications taken, allergies , and past experiences with anesthesia.
Cardiac valve repair or replacement often requires a 2–3 day postoperative stay in an ICU, a 2–3 week stay in the hospital, and several months of cardiac rehabilitation therapy. These times may be shortened if minimally invasive procedures have been performed.
Recovery from cardiac valve surgery is a slow process that can stretch to six months or more depending on the age and health of the patient. Initially, care givers will need to be continuously available, with the need for assistance in routine self-care decreasing as the patient becomes stronger. Frequent check-ups are required following cardiac valve surgery, with the time between doctor visits lengthening as the patient heals.
Patients who have valve repair or who receive a tissue valve replacement must take blood-thinning medications for several months. Those who receive a mechanical valve replacement must take blood-thinning medications for the remainder of their lives. Patients who receive either type of valve must take antibiotics before having dental work, surgery, or certain invasive tests. This is to reduce the chance of heart infection (endocarditis).
Arrhythmia —An abnormal heart rhythm.
Congestive heart failure —A condition in which the heart is weakened and cannot pump all the blood that is returned to it from the body. As a result, fluid builds up in tissues and in the lungs.
Cardiac rehabilitation —A structured program of education and activity offered by hospitals and other organizations.
Doppler echocardiography —A testing technique that uses Doppler ultrasound technology to evaluate the pattern and direction of blood flow in the heart.
Echocardiogram —A non-invasive imaging procedure used to create a picture of the heart's movement, valves, and chambers.
Endocarditis —Infection of the heart endocardium tissue, the inner most tissue and structures of the heart.
Transesophageal echocardiography —A diagnostic test using an ultrasound device that is passed into the esophagus of the patient to create a clear image of the heart muscle and other parts of the heart.
The risks of cardiac valve surgery include death, stroke , heart attack , heart arrhythmias, kidney failure, excessive bleeding, and infection. Long-term risks following successful surgery include and the development of blood clots that can cause stroke or heart attack and endocarditis. The presence of a mechanical valve may prevent the patient from having certain routine tests such as a chest MRI (an MRI makes the metal in the valve heat up). Rarely a metal valve may set off an airport or similar metal detector.
The death rate during or shortly after surgery is between 2 and 3% and varies with the valve replaced and the age and health of the individual. Most people who have cardiac valve surgery see both an improvement in the quality and length of their life. For example, the nine-year survival rate for people having mitral valve replacement is about 65%. About 90% of people who have valve repair need no additional surgeries. The exception is those patients whose defects in valve function are caused by disease. In these people, even after repair, the valve may continue to degenerate and need replacement.
Cardiac valve surgery is performed by a cardiothoracic surgeon who often specializes only in valve surgery. The surgeon is assisted by additional physicians such as an anesthesiologist and by specially trained cardiac nurses. The heart-lung machine is operated by a highly trained technician.
“Heart Valve Surgery.” Cleveland Clinic. November 2007 [cited February 28, 2008]. http://www.clevelandclinic.org/heartcenter/pub/guide/disease/valve/valvetreatment.htm.
“Heart Valve Surgery.” Medline Plus. February 20, 2008 [cited February 28, 2008]. http://www.nlm.nih.gov/medlineplus/ency/article/002954.htm.
“Valve Replacement. Valve Repair Surgery.” Society of Thoracic Surgeons. [cited February]. http://www.sts.org/sections/patientinformation/valvesurgery.
American Heart Association, 7272 Greenville Avenue, Dallas, TX, 75231, (800) 242-8721, http://www.americanheart.org.
National Heart Lung and Blood Institute Health Information Center, P.O. Box 30105, Bethesda, MD, 20824-0105, 301) 592 8573; TTY: (240) 629-3255, (240) 629-3246, [email protected], http://www.nhlbi.nih.gov.
Tish Davidson A. M.