Section 3. Heart and Blood Vessel Disorders

Chapter 28. Heart Valve Disorders

Topics: Introduction | Mitral Regurgitation | Mitral Valve Prolapse | Mitral Stenosis | Aortic Regurgitation | Aortic Stenosis | Tricuspid Regurgitation | Tricuspid Stenosis | Pulmonary Stenosis

Mitral Stenosis

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

See the animation Understanding Mitral Valve Stenosis.

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.

Mitral stenosis almost always results from rheumatic fever, a childhood illness that sometimes occurs after untreated strep throat or scarlet fever (see Section 23, Chapter 272). Rheumatic fever is now rare in North America, Australasia, and Western Europe because antibiotics are widely used to prevent 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 immigrants. In regions where antibiotics are not widely used, 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 also be present at birth (congenital). Infants born with the disorder rarely live beyond age 2, unless they have surgery.

Two conditions unrelated to mitral stenosis can produce the same effects as the stenosis. They include a myxoma (a noncancerous tumor in the left atrium) and a blood clot that reduces blood flow through the mitral valve.

Symptoms and Diagnosis

If mitral stenosis is severe, pressure increases in the left atrium and in the veins of the lungs, resulting in heart failure with fluid accumulation in the lungs. If a woman with severe mitral stenosis becomes pregnant, heart failure may develop rapidly. People with heart failure become easily fatigued and short of breath. Shortness of breath may occur only during physical activity at first, but later, it may occur even during rest. Some people can breathe comfortably only when they are propped up with pillows or sitting upright.

Severe mitral stenosis may result in high blood pressure in the lungs (pulmonary hypertension) and a low level of oxygen in the blood. This combination of problems produces a plum-colored flush in the cheeks (called mitral facies). People may cough up blood if the high pressure causes a vein or capillaries in the lungs to burst. The resulting bleeding into the lungs is usually slight and rarely massive.

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.

With a stethoscope, doctors can 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 electrocardiography (ECG), a chest x-ray showing an enlarged atrium, or echocardiography, which uses ultrasound waves to produce an image of blood passing through the narrowed valve opening. If surgery is being considered, cardiac catheterization (see Section 3, Chapter 21) is necessary to further define the extent and characteristics of the blockage.

Prevention and Treatment

Mitral stenosis can be prevented only by preventing rheumatic fever, which can be prevented by promptly treating strep throat or scarlet fever with antibiotics.

Treatment includes use of diuretics and digoxin. Diuretics, which increase urine formation, can reduce blood pressure in the lungs by reducing the volume of circulating blood. Digoxin is useful only in the treatment of atrial fibrillation, which may be present. Digoxin slows the heart rate in people with atrial fibrillation so that the blood has more time to flow through the narrowed valve opening. However, atrial fibrillation may require additional treatment (see Section 3, Chapter 27).

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 valvuloplasty. In this procedure, a balloon-tipped catheter is threaded through a vein and eventually into the heart (see Section 3, Chapter 21). Once inside the valve, the balloon is inflated, separating the valve leaflets. 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.

People with mitral stenosis are given antibiotics before a surgical, dental, or medical procedure (see Section 3, Chapter 29) to reduce the small risk of developing a heart valve infection (infective endocarditis).