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Mitral stenosis (mitral valve stenosis) is a narrowing of the mitral valve opening that slows blood flow from the left atrium to the left ventricle.
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—see Abnormal Heart Rhythms: Atrial Fibrillation and Atrial Flutter). As a result, the heart's pumping efficiency is reduced. 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 (see Bacterial Infections in Infants and Children: Rheumatic Fever). Rheumatic fever is now rare in North America, Australasia, 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.
Mitral stenosis can rarely be present at birth (congenital). Infants born with the disorder rarely live beyond age 2, unless they have surgery.
Symptoms and Diagnosis
Mild mitral stenosis does not usually cause symptoms. Eventually the disorder progresses and people develop symptoms such as becoming easily tired and shortness of breath. 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.
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.
Prevention and Treatment
Mitral stenosis will not occur if rheumatic fever is prevented by promptly treating strep throat with antibiotics.
Treatment 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 may be 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.
Sometimes the valve can be stretched open using a procedure called balloon valvotomy. In this procedure, a balloon-tipped catheter is threaded through a vein and eventually into the heart (see Diagnosis of Heart and Blood Vessel Disorders: Cardiac catheterization). Once inside the valve, the balloon is inflated, separating the valve cusps. Alternatively, heart surgery may be performed 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 Which Procedures Require Preventive Antibiotics?* ) to reduce the small risk of developing a heart valve infection (infective endocarditis).
Last full review/revision March 2013 by Guy P. Armstrong
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