Mitral stenosis is an obstruction to left ventricular inflow at the mitral valve level due to the structural abnormality of the mitral valve apparatus. Rheumatic fever is a main cause of mitral stenosis. Other uncommon etiologies include congenital mitral stenosis, such as parachute mitral valve; marked mitral annular calcification of the mitral valve; and infective endocarditis with large vegetations (often fungal). Sometimes, conditions such as left atrial myxoma can mimic mitral stenosis by obstructing outflow.
Since acute rheumatic fever is mild in nature, only fewer than half of patients with mitral stenosis give a clear history of being affected by it. As no specific tests are available, acute rheumatic fever is often underdiagnosed.
Stenosis of the mitral valve typically occurs decades after the episode of acute rheumatic fever. Pathologically, multiple inflammatory foci (Aschoff bodies, ie, perivascular mononuclear infiltrate) develop in the endocardium and myocardium after the initial insult. Sometimes, this might lead to the acute development of small vegetations along the border of the valves.
Over time, progression of the disease leads to reaction and adhesion of commissures, thickening and shortening of chordae tendineae, thickening of the valve leaflets, and ultimately deposition of calcium in the valve leaflets and/or the subvalvular apparatus. Slowly, the valve apparatus starts to retract and becomes contracted and stenotic. Whether the progression of valve damage is due to hemodynamic injury of the already affected valve apparatus or to the chronic inflammatory nature of the rheumatic process is unclear.
The normal mitral valve orifice area is approximately 4-6 cm2. As the orifice size decreases, pressure gradient across the mitral valve increases to maintain adequate flow (Bernoulli principle).
Patients will be asymptomatic until the valve area reaches 2 cm2. Although they may not have any symptoms at rest, moderate exercise or any factors that increase the heart rate will result in exertional dyspnea. This is due to increased transmitral gradient causing higher pulmonary wedge pressure.
Severe mitral stenosis occurs with a valve area less than 1 cm2. As the valve progressively narrows, the resting diastolic mitral valve gradient, and hence left atrial pressure, increases. This leads to transudation of fluid into the lung interstitium and decreased pulmonary compliance with dyspnea at rest or with minimal exertion. Hemoptysis may occur because of the rupture of bronchial veins. The elevated pressure in the left atrium provokes its dilatation and increases the risk of atrial fibrillation, with subsequent left atrial appendage thrombus formation and thromboembolism.
Pulmonary hypertension develops because of (1) retrograde transmission of left atrial pressure, (2) pulmonary arteriolar constriction, (3) interstitial edema, and (4) obliterative changes in the pulmonary vascular bed. These changes in the pulmonary vascular bed protect the pulmonary capillaries from the surge of blood passing into the capillaries during activity and thus from pulmonary congestion. As pulmonary hypertension increases, right ventricular dilation occurs, which leads to tricuspid regurgitation. Right ventricular failure leads to elevated jugular venous pressure, liver congestion, ascites, and pedal edema.
Left ventricular end-diastolic pressure and cardiac output are usually normal in persons with isolated mitral stenosis. However, associated significant mitral regurgitation, systemic hypertension, aortic stenosis, and myocardial infarction can affect left ventricular function and lead to decreased cardiac output. Approximately one third of patients with mitral stenosis have depressed left ventricular systolic function (ejection fraction 0.35-0.50) based on rheumatic heart disease (ie, no evidence of coronary artery disease).
The prevalence of rheumatic disease among persons in developed nations, such as the United States, is steadily declining. An estimated 1 in 100,000 people are affected.
The prevalence is higher in developing nations. In India, for example, the prevalence is approximately 100-150 cases per 100,000 people.
The 10-year survival rate for asymptomatic persons is approximately 80%.
The 10-year survival rate for patients with mild symptoms is approximately 60%.
The 10-year survival rate among patients who develop congestive heart failure is 15%. See Medscape’s Heart Failure Resource Center.
For reasons not clearly known, mitral stenosis is more common in females than in males. Nearly two thirds of patients with mitral stenosis are female.
The onset of symptoms usually occurs between the third and fourth decade of life.
Symptoms of mitral stenosis usually develop in the third or fourth decade of life. Nearly half of the patients do not recall a history of acute rheumatic fever.
The rate of disease progression is faster in patients in developing countries and slower in patients in Western countries.
The patient is generally asymptomatic in the early phase of the disease. However, factors that increase the heart rate precipitate dyspnea by increasing the gradient between the left atrium and the left ventricle. These factors include fever, severe anemia, thyrotoxicosis, sexual intercourse, exercise, excitement, pregnancy, paroxysmal tachycardia, and atrial fibrillation.
As the disease progresses, the patient develops dyspnea on exertion, orthopnea, paroxysmal nocturnal dyspnea, and atrial arrhythmia.
Nearly 15% of patients develop embolic episodes that are usually associated with atrial fibrillation. Rarely, embolic episodes have developed in patients with sinus rhythm.
Systemic embolization leads to stroke, renal failure, and myocardial infarction.
Hoarseness can develop from compression of the left recurrent laryngeal nerve against the pulmonary artery by an enlarged left atrium. Also, compression of bronchi by the enlarged left atrium can cause a persistent cough.
Hemoptysis may occur and is usually not fatal. It occurs because of the rupture of thin, dilated bronchial veins due to left atrial hypertension.
Pregnant women with mild mitral stenosis may become symptomatic during their second trimester because of the increase in blood volume and cardiac output.
Some patients present with chest pain, the reason for which is not clearly known. Most of the time, chest pain can be related to pulmonary hypertension, coronary embolization, or coronary atherosclerosis.
Patients may develop pinkish-purple patches (malar flush) on their cheeks, which usually correlates with severe mitral stenosis due to reduced cardiac output and vasoconstriction.
The jugular vein is distended. In patients with sinus rhythm, a prominent a wave is noted, which reflects increased right atrial pressure from pulmonary hypertension and right ventricular failure. A prominent v wave is noted in patients with significant tricuspid regurgitation.
The apical impulse may be laterally displaced or may not be felt, especially in cases of severe mitral stenosis. This can be explained by the decreased left ventricular filling. However, a right ventricular heave can be palpated because the enlarged left atrium displaces the right ventricle anteriorly. Rarely, a diastolic thrill can be felt at the apex with the patient in the left lateral recumbent position.
The auscultatory findings characteristic of mitral stenosis are a loud first heart sound, an opening snap, and a diastolic rumble.
The first heart sound is accentuated because of a wide closing excursion of the mitral leaflets. The degree of loudness of the first heart sound depends on the pliability of the mitral valve. The intensity of the first heart sound diminishes as the valve becomes more fibrotic, calcified, and thickened.
The second heart sound is normally split, and the pulmonic component is accentuated if pulmonary hypertension is present. The opening snap follows the second heart sound. The sudden tensing of the valve leaflets after they have completed their opening excursion causes an opening snap. In patients with elevated left atrial pressure and hence with severe mitral stenosis, the opening snap occurs closer to the second heart sound.
The diastolic murmur of mitral stenosis is of low pitch, rumbling in character, and best heard at the apex with the patient in the left lateral position. It commences after the opening snap and the duration of the murmur correlates with the severity of the stenosis. It is absent in persons with severe disease. The murmur is accentuated by exercise, cough, and amyl nitrate, whereas it decreases with rest and with Valsalva maneuver. In patients with sinus rhythm, the murmur increases intensity in late diastole (so called, presystolic accentuation) due to increased flow across the stenotic mitral valve as a result of left atrial contraction.
Diastolic murmurs secondary to pulmonary regurgitation and aortic regurgitation might be present.