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Mitral Stenosis

(Mitral Valve Stenosis)

By Guy P. Armstrong, MD

Mitral stenosis is a narrowing of the mitral valve opening that blocks (obstructs) blood flow from the left atrium to the left ventricle.

  • Mitral stenosis usually results from rheumatic fever, but infants can be born with the condition.

  • Mitral stenosis does not cause symptoms unless it is severe.

  • Doctors make the diagnosis after hearing a characteristic heart murmur through a stethoscope placed over the heart, and they use echocardiography to make a more detailed diagnosis.

  • Treatment begins with use of diuretics and beta-blockers or calcium channel blockers.

  • The valve can be stretched open with a catheter, but occasionally the valve needs to be replaced, requiring open-heart surgery.

The mitral valve is in the opening between the left atrium and the left ventricle. The mitral valve opens to allow blood from the left atrium to fill the left ventricle and closes as the left ventricle contracts to pump blood into the aorta. If a disorder causes the valve flaps to become thick and stiff, the valve opening is narrowed. Sometimes the stiffened valve also fails to close completely, and mitral regurgitation develops.

In mitral stenosis, blood flow through the narrowed valve opening is reduced. As a result, the volume and pressure of blood in the left atrium increases, and the left atrium enlarges. The enlarged left atrium often beats rapidly in an irregular pattern (a disorder called atrial fibrillation). As a result, the heart's pumping efficiency is reduced because the fibrillating atrium is quivering rather than pumping. Consequently, blood does not flow through the atrium briskly, and blood clots may form inside the chamber. If a clot breaks loose (becoming an embolus), it is pumped out of the heart and may block an artery, possibly causing a stroke or other damage.

If mitral stenosis is severe, pressure increases in the blood vessels of the lungs, resulting in heart failure with fluid accumulation in the lungs and a low level of oxygen in the blood. If a woman with severe mitral stenosis becomes pregnant, heart failure may develop rapidly.

Causes

Mitral stenosis almost always results from rheumatic fever, a childhood illness that occurs after some cases of untreated strep throat or scarlet fever. Rheumatic fever is now rare in North America and Western Europe because antibiotics are widely used to treat infection. Thus, in these regions, mitral stenosis occurs mostly in older people who had rheumatic fever and who did not have the benefit of antibiotics during their youth or in people who have moved from regions where antibiotics are not widely used. In such regions, rheumatic fever is common, and it leads to mitral stenosis in adults, teenagers, and sometimes even children. Typically, when rheumatic fever is the cause of mitral stenosis, the mitral valve cusps are partially fused together.

Less often, in some older people, the valve instead degenerates and accumulates calcium deposits. In these people, mitral stenosis tends to be less severe.

Mitral stenosis can rarely be present at birth (congenital). Infants born with the disorder rarely live beyond age 2, unless they have surgery.

Symptoms

Mild mitral stenosis does not usually cause symptoms. Eventually the disorder progresses and people develop symptoms such as shortness of breath and becoming easily tired. People with atrial fibrillation may feel palpitations (awareness of heartbeats).

Once symptoms start, people become severely disabled in about 7 to 9 years. Shortness of breath may occur even during rest. Some people can breathe comfortably only when they are propped up with pillows or sitting upright. Those people with a low level of oxygen in the blood and high blood pressure in the lungs may have a plum-colored flush in the cheeks (called mitral facies).

People may cough up blood (hemoptysis) if the high pressure causes a vein or capillaries in the lungs to burst. The resulting bleeding into the lungs is usually slight, but if hemoptysis occurs, the person should be evaluated by a doctor promptly because hemoptysis indicates severe mitral stenosis or another serious problem.

Diagnosis

  • Physical examination

  • Echocardiography

With a stethoscope, doctors may hear the characteristic heart murmur as blood tries to pass through the narrowed valve opening from the left atrium into the left ventricle. Unlike a normal valve, which opens silently, the abnormal valve often makes a snapping sound as it opens to allow blood into the left ventricle. The diagnosis is usually confirmed by echocardiography, which uses ultrasound waves to produce an image of the narrowed valve and the blood passing through it. Electrocardiography (ECG) and chest x-rays also provide useful information.

Treatment

  • Sometimes valve repair or replacement

Mitral stenosis will not occur if rheumatic fever is prevented by promptly treating strep throat with antibiotics.

People who have no symptoms do not need treatment.

Treatment, when needed, includes use of diuretics and beta-blockers or calcium channel blockers. Diuretics, which increase urine production, can reduce blood pressure in the lungs by reducing blood volume. Beta-blockers, digoxin, and calcium channel blockers help slow the abnormal heart rate that can occur with atrial fibrillation. Anticoagulants are needed to prevent blood clot formation in people with atrial fibrillation.

If drug therapy does not reduce the symptoms satisfactorily, the valve may be repaired or replaced.

Often the valve can be stretched open using a procedure called balloon valvotomy. In this procedure, a catheter with a balloon on the tip is threaded through a vein and eventually into the heart (see Cardiac catheterization). Once across the valve, the balloon is inflated, separating the valve cusps. Alternatively, heart surgery may be done to separate the fused cusps. If the valve is too badly damaged, it may be surgically replaced with an artificial valve.

If the valve has been replaced, people are given antibiotics before a surgical, dental, or medical procedure (see Table: Which Procedures Require Preventive Antibiotics*?) to reduce the small risk of developing a heart valve infection (infective endocarditis).

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