Function of the Mitral Valve
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The mitral valve lies between the left atrium and the left ventricle. Blood enriched with oxygen flows from the lungs into the atrium and through the mitral valve into the left ventricle. From there it flows on into the body. The mitral valve prevents blood from flowing back into the atrium in this phase.
The mitral valve consists of a front (anterior) and back (posterior) leaflet. The leaflets are attached to a ring of connective tissue, which belongs to the scaffold of the heart. When the blood flows from the atrium into the ventricle, the leaflets close off the blood flow like gates. They cannot prolapse into the atrium since they are attached to the ventricle wall with sinewy threads (the chordae tendineae) that are just long enough for the leaflets to remain in position at the closure level.
Diseases of the Mitral Valve
Mitral Valve Stenosis
When the mitral valve leaflets no longer open sufficiently for the blood to flow from the atrium into the ventricle, the valve is stenosed. Today this condition is only rarely seen in the industrialized countries, since the main cause, rheumatic fever, has been almost completely eradicated. When mitral valve stenosis occurs, repair is usually not possible – the valve has to be replaced.
Mitral Valve Insufficiency
Mitral valve insufficiency is the most frequent disease of the mitral valve. It is present when the mitral valve leaflets no longer lie close to each other during the ejection phase of the heart. This means that some of the blood that should be pumped from the left ventricle into the body’s circulation flows back into the atrium, which puts a strain on the heart. Mitral valve insufficiency can be caused by degeneration of the valve and the chordae tendineae (primary mitral valve insufficiency) or by a change in the dimensions of the left ventricle, caused for example by a myocardial infarction (secondary mitral valve insufficiency).
Primary mitral valve insufficiency is the most common form. It mostly arises when the sinewy threads attached to the valve become stretched, so that a leaflet prolapses into the atrium. With secondary mitral valve insufficiency the valve leaks due to an increase in the size of the ventricle. This causes the threads to exercise too strong a force on the valve. The valve can then no longer close properly.
The most frequent symptom of mitral valve insufficiency is shortness of breath. This may not occur until the disease is very advanced. Often the problem is discovered by chance during routine examinations, for example through the presence of a typical heart sound during the heart’s blood ejection phase.
Diagnosis
The most important method of diagnosing a heart valve disease is echocardiography, or sonographic examination of the heart. Further methods are ECG, a heart X-ray and possibly also a computed tomography (CT) examination to plan the necessary procedure. Before the operation a heart catheterization is performed to rule out disease of the coronary arteries (primary insufficiency) and to establish whether heart muscle tissue can be saved (secondary insufficiency).
Treatment
Surgery on the Mitral Valve
A severely leaking mitral valve must be operated upon. In over 90 percent of cases the surgeons can reconstruct the valve and restore its natural function. To stabilize the valve a ring is sewn on to the mitral valve annulus to reduce its diameter. This brings the leaflets closer together so that the valve can close again. If the mitral valve is too severely degenerated it must be replaced with a biological or mechanical prosthesis. Both types of prostheses have advantages and disadvantages (see Aortic Valve Surgery), which the surgeon will discuss with the patient before the operation.
At the German Heart Center Berlin the standard procedure is for the mitral valve to be operated upon by minimally invasive access, through a small incision on the right side of the chest, via the left atrium. Only when an additional procedure such as a bypass operation is necessary must the breastbone be severed – the conventional access route to the heart.
Special cameras and monitors give the surgeon a three-dimensional view of the operation site. During the operation the heart must be stopped and its function is taken on by the heart-lung machine. After the operation the patient’s own circulation is started again. An ultrasound probe introduced through the esophagus is then used to check that the operation has been successful.
Treatment by Heart Catheterization
For patients for whom an operation with the heart-lung machine represents a high risk the procedure can be performed with a heart catheter. The catheter is advanced through an incision in the groin to the heart. It carries a so-called MitraClip, which is used to create a “bridge” at the point of leakage. However, it is often not possible to completely resolve the leakage. The valve can also become insufficient again more quickly than with an operation.