Mitral valve repair and replacement
Heart valves are designed to control the direction of blood flow through the heart. The opening and closing of the heart valves produce the sound of the heartbeat. Mitral valve replacement surgery is used to replace a diseased mitral heart valve with a natural or artifical valve. Mitral valve replacement surgery is open-heart surgery that is done while the patient is under general anesthesia. An incision is made through the breast bone (sternum). Tubes are used to re-route the blood away from the
heart to a heart-lung bypass machine to keep the blood oxygenated and circulating while the heart is being operated on.
The heart's valves perform the important function of ensuring blood flow in the correct direction. The mitral valve directs the flow of blood from the left atrium into the left ventricle, and the aortic valve allows blood to pass from the left ventricle into the aorta. The tricuspid and pulmonary valves perform the equivalent task on the right side but are under considerably less pressure and, although they may suffer from similar disorders, are less likely to be so severely impaired as to require surgery. When the valve opening between the upper and lower chambers on the left side of the heart (mitral valve) becomes severely blocked (mitral stenosis), it usually requires surgery. Because the narrowing of the valve may cause blood to back up into the lungs, careful monitoring of symptoms such as shortness of breath is required, and surgery may be necessary to prevent serious heart failure. When the mitral valve closes improperly (mitral insufficiency or regurgitation), the desirability of surgery is usually determined by how severely the symptoms affect the patient's lifestyle and how well they can be controlled by medical treatment.
Mitral valve problems are rarely caused by a birth defect, otherwise known as a congenital condition. More often, simple "wear and tear" may cause part of the valve mechanism to fail. This is called "degenerative disease". This may be related to advancing age, although many young people will have this condition as well. Rheumatic fever may damage the mitral valve causing stenosis or regurgitation. Occasionally the mitral valve is damaged by infection or bacterial endocarditis. Ischemic heart disease (coronary artery disease) can also cause the mitral valve to leak.
Many mitral valves can be repaired, especially if they leak due to degenerative disease. A separate discussion of mitral valve repair will be available through this site. In many cases, however, the valve is too damaged to permit repair and the valve must be replaced with a prosthetic (artificial) valve. Valves damaged by rheumatic disease often must be replaced.
In general terms, there are two types of artificial valves available - mechanical valves made entirely from metal and pyrolytic carbon - or biological valves - made from animal tissues. Each has advantages and disadvantages with respect to durability (how long they will last) and risk of blood clots forming on the valve
There are a number of excellent mechanical prostheses available today. All perform equally well. The principle advantage of mechanical valves is their excellent durability. The valves available today simply do not wear out! Their main disadvantage is that blood has a tendency to clot on all mechanical valves. If this happens the valve will not function normally. Therefore, patients with these valves must take anticoagulants (blood thinners) for life. There is also a small but definite risk of blood clots causing stroke, even when taking anticoagulants.
There are a variety of biological alternatives for mitral valve replacement. Most are made from pig aortic valves. Their key advantage is that they have a reduced risk of blood clots forming on the valve itself causing valve dysfunction or stroke. The key disadvantage of biological or tissue valves is that they have more limited durability as compared with mechanical valves. They will wear out given enough time. The rate at which they wear out, however, depends on the patient's age. A young boy might wear out such a valve in only a few years, while the same valve might last 10 years in a middle aged person, and even longer in a patient over the age of 70. Of course, as we grow older we expect that we will not need the valve for as many years as our life expectancy is less. The general consensus is that a tissue valve will not need to be replaced if used in a patient over the age of 70 years.
Often the mitral valve is so damaged that it must be replaced (refer to Mitral Valve Replacement). Occasionally, however, the valve can be repaired rather than replaced. One type of repair is a procedure called mitral commisurotomy. Mitral commisurotomy can be performed for some valves that are narrow or "stenotic" either from birth or from damage by rheumatic fever. Most often today, rheumatic mitral stenosis is treated by balloon valvuloplasty, a procedure performed in the cardiac catheterization laboratory by interventional cardiologists. Using a catheter with a balloon on the end, the balloon is expanded inside the valve "stretching" it open.
More often mitral valve repair is performed to correct a leaking or regurgitant valve. Congenital mitral regurgitation may be due to a cleft mitral valve (a valve with a separation or cleft down the middle) associated with an atrial septal defect, a type of hole in the heart between the low pressure chambers or atria. Such valves can sometimes be repaired simply by closing the cleft with sutures. Valves regurgitant due to bacterial endocarditis can occasionally be repaired, however the majority of mitral valve repairs are performed for degenerative disease. Degenerative mitral valve disease may be due to an elongation or rupture of the chordal apparatus, the "heart-strings" that support the valve normally, or due to a more generalized weakness of the valve itself such as the "floppy valve" syndrome in which all of the components of the valve are enlarged and elongated.
Not all mitral valves can be repaired. A preoperative echocardiogram may help your surgeon predict the likelihood of repair, but cannot guarantee it. Mitral valves that are regurgitant due to rheumatic fever are often both stenotic and regurgitant, and are often beyond repair.