Mitral valve replacement
Mitral valve replacement is a surgical procedure in which the diseased mitral valve of the heart is replaced by a mechanical or biological tissue valve.
The mitral valve can become diseased, preventing it from adequately controlling the direction of the flow of blood between the left atrium and left ventricle. It also can become insufficient (regurgitant) and allow blood to flow backwards into the left atrium from the left ventricle during ventricular contraction (systole). In addition, the mitral valve can become stenotic (narrowed), preventing the flow of blood from the left atrium into the left ventricle during ventricular filling (diastole). In mitral valve prolapse, one or more of the mitral valve's cusps protrude back into the left atrium during ventricular contraction. Mitral valve replacement is performed to remove the diseased valve and provide a new mechanical valve or biological tissue valve that correctly controls the direction of blood flow.
Approximately 65,000 valve repairs and replacements are performed in the United States each year.
Twice as many women as men are affected by mitral valve stenosis. About 60% of patients with mitral valve stenosis have had rheumatic fever. After rheumatic fever there is usually a latency period of 10–20 years before symptoms of mitral valve stenosis appear. The prevalence of mitral valve stenosis has declined in the United States because there has been a decline in the number of cases of rheumatic fever. Mitral valve stenosis may be present at birth (congenital); however, it rarely occurs alone but rather in conjunction with other heart defects.
Mitral valve prolapse is the most common condition of the heart valves, and is present in about 2% of the general population. Recent studies indicate that similar numbers of men and women have mitral valve prolapse. Having this condition does not guarantee that mitral insufficiency will develop. Patients with a history of rheumatic fever, coronary artery disease, infective endocarditis, or collagen vascular disease also may develop mitral insufficiency.
Cardiac monitoring is instituted and general anesthesia is provided. The surgeon uses a sternotomy to access the heart and great blood vessels. Anticoagulation is given as cannulae are inserted into the large vessels of the heart, femoral vessels, or a combination. Cardiopulmonary bypass is instituted. The heart is arrested as the cross clamp is applied to the ascending aorta to stop blood flow through the organ. The surgeon opens the heart to visualize the mitral valve. He/she may expose the mitral valve by opening the right atrium and then opening the atrial septum. Another approach requires a large left atrium that can be opened directly, making the mitral valve visible.
Next, the surgeon cuts the diseased valve away from the valve annulus (outer ring). The annulus is sized so that the proper size of valve can be selected for the patient's anatomy. Sutures are applied around the valve annulus, the valve is sutured into place, and tied into position. The atrial septum is closed with suture or left to heal naturally, and the heart is closed with sutures.
Deairing of the heart is performed prior to removal of the cross clamp. When the cross clamp is removed, deairing continues to ensure that no air is delivered to the systemic circulation. At this time a transesophageal echocardiogram (TEE) may be used to test that the valve is functioning correctly and that the heart is free of air. Once the surgeon is satisfied that the valve is working correctly, cardiopulmonary bypass is terminated, anticoagulation is reversed, and the cannulae are removed from the vessels. The sternotomy is closed. Permanent stainless steel wires are used to hold the sternum bone together. The skin incision is closed with sutures, and sterile bandages are applied to the wound.
A heart valve is a structure within the heart that prevents the backflow of blood by opening and closing with each heartbeat. Replacement heart valves are either mechanical or biological tissue valves. For patients under the age of 65, the mechanical valve offers superior longevity, but the use of this type of valve requires that the patient take an anticoagulation drug for the rest of his/her life. The biological tissue valve does not require anticoagulation therapy, but this type of valve is prone to deterioration leading to reoperation , particularly in those under the age of 50. Women who may want to have children after a valve replacement should usually receive a biological tissue valve, because the anticoagulant (Coumadin/warfarin) most often prescribed for patients with mechanical valves is associated with fetal birth defects. Aspirin can be substituted for warfarin in certain circumstances.
Mitral valve stenosis is diagnosed by history, physical examination , listening to the sounds of the heart (cardiac auscultation), chest x ray , and ECG. Patients may have no symptoms of a valve disorder or may have shortness of breath (dyspnea), fatigue, or frank pulmonary edema. Other patients present with atrial fibrillation (a cardiac arrhythmia) or an embolic event. Doppler echocardiography is the preferred diagnostic tool for evaluation of mitral valve stenosis, and it can be performed in conjunction with non-invasive exercise testing by treadmill or bicycle. Cardiac catheterization is reserved for patients who demonstrate discrepancies in Doppler testing. Both left- and right-heart catheterization should be performed in the presence of elevated pulmonary artery pressures.
A diagnosis of mitral insufficiency requires a detailed patient history. Listening to the heart (auscultation) reveals the presence of a third heart sound. Chest x ray and ECG provide additional information. Again, Doppler echocardiography provides valuable information. Exercise testing with Doppler echocardiography can show the true severity of the disease.
After initial findings, patients may be followed with repeat visits and testing to monitor disease progress. If the patient has reached NYHA Class III or IV, replacement is considered. Severe pulmonary hypertension with pulmonary artery systolic pressures greater than 60 mm Hg is considered an indication for surgery. Left ventricular ejection fraction (a measure of output) less than 60% also is an indication for surgery.
The patient receives continued cardiac monitoring in the intensive care unit and usually remains in intensive care for 24–48 hours after surgery. Ventilation support is discontinued when the patient is able to breathe on his/her own. If mechanical circulatory support and inotropic agents (a substance that influences the force of muscle contractions, e.g. digitalis) were needed during the surgical procedure, they are discontinued as cardiac function recovers. Tubes draining blood from the chest cavity are removed as bleeding from the surgical procedure decreases. Prophylactic antibiotics are given to prevent infective endocarditis and the recurrence of rheumatic carditis.
Both mechanical and biological tissue valves require anticoagulation therapy after surgery, and while patients are hospitalized their anticoagulant status is monitored and dosages are adjusted accordingly. Patients with biological tissue valves can discontinue anticoagulation therapy within three months of implantation, but those with mechanical valves must take an anticoagulant (aspirin, warfarin, or a combination of the two) for the rest of their lives. These patients are regularly monitored for INR values, which are maintained between 2.0 and 4.5.
If the patient recovers normally, discharge from the hospital occurs within a week of surgery. At discharge, the patient is given specific instructions about wound care and infection recognition, as well as contact information for the physician and guidelines about when a visit to the emergency room is indicated. Within three or four weeks after discharge, the patient is seen for follow-up office visit with the physician, at which time physical status will have improved for evaluation. Thereafter, asymptomatic, uncomplicated patients are seen at yearly intervals. Few limitations are placed on patient activity once recovery is complete.
There are always risks associated with general anesthesia and cardiopulmonary bypass. Risks specifically associated with mitral valve replacement include embolism, bleeding, and operative valvular endocarditis. Hemolysis (the breakdown of red blood cells) is associated with certain types of mechanical valves, but is not a contraindication for implantation.
Patients treated by mitral valve replacement for mitral insufficiency can expect relief of symptoms. Improvement in myocardial function is not likely, but the current status is preserved. For patients who received mechanical valves, anticoagulation therapy is continued lifelong to elevate the INR to between 2.0 and 4.5, depending on the type of mechanical valve implanted. Since thromboembolic complications are associated with initial implant of biological tissue valves, patients who received this type of valve take an anticoagulant for three months after surgery to maintain an INR of 2.0–3.0. If non-cardiac surgery or dental care is needed, the anticoagulation therapy is adjusted to prevent bleeding complications.
Patients who undergo mitral valve replacement for mitral stenosis can expect excellent improvement of symptoms. Those patients with symptoms consistent with NYHA class IV before surgery have better outcome after mitral valve replacement compared to no treatment.
Morbidity and mortality rates
Mitral valve replacement carries a less than 5% risk of death in young, healthy patients. With increased age, additional medical problems, or pulmonary hypertension the risk of death increases to 10–20%. Post-replacement the five year survival is 80%. Patients over the age of 75 have poorer outcomes when mitral valve replacement is used to treat mitral insufficiency.
The asymptomatic patient with a history of rheumatic fever can be treated with prophylactic antibiotics and followed until symptoms are appear. If atrial fibrillation develops, antiarrhythmic medications can be used for treatment. Atrial defibrillation may relieve atrial fibrillation. Anticoagulants may be prescribed to prevent the occurrence of systemic embolization. The patient with symptoms may benefit from percutaneous mitral balloon valvotomy. Surgery to perform a commissurotomy may be used instead of valve replacement.
Mitral valve insufficiency or prolapse that develops atrial fibrillation should be treated with drugs to regulate the heart rhythm or atrial defibrillation. Anticoagulation therapy is employed to avoid systemic emboli during periods of atrial fibrillation. Mitral valve repair maybe beneficial instead of mitral valve replacement.
Hensley, Frederick A., Donald E. Martin, and Glenn P. Gravlee, eds. A Practical Approach to Cardiac Anesthesia. 3rd ed. Philadelphia: Lippincott Williams & Wilkins, 2003.
Topol, Eric J., ed. Textbook of Interventional Cardiology. Philadelphia: W. B. Saunders, 2002.
Bonow, R., et al. "ACC/AHA Guidelines for the Management of Patients with Valvular Heart Disease." Journal of the American Collge of Cardiology 32 (November 1998): 1486–1582.
Brown, Katherine Kay. "Minimally Invasive Valve Surgery." Critical Care Nursing Quarterly 20 (February 1998): 40–52.
Sadovsky, Richard. "Using Warfarin After Heart Valve Replacement." American Family Physician 61 (April 1, 2000): 2219.
Allison Joan Spiwak, MSBME
WHO PERFORMS THE PROCEDURE AND WHERE IS IT PERFORMED?
Cardiothoracic and cardiovascular surgeons provide surgical treatment. Surgeons are trained during the residency to perform these procedures. Medical centers that perform cardiac surgery are able to provide mitral valve replacement.
QUESTIONS TO ASK THE DOCTOR
- Is mitral valve replacement the best treatment option for my condition?
- How many of these procedures has the surgeon performed in the last year? in the last five years?
- What is the surgeon's morbidity and mortality rate with mitral valve replacement?
- What type of replacement valve, biological tissue or mechanical, is best for me?
- What are the pros and cons of each valve type?
- What type of follow-up care is required during the first year after valve implant and for the rest of my life?
- What types of complications are associated with this surgery?