Mitral Stenosis

Introduction
Background

Mitral stenosis (MS) is characterized by obstruction to left ventricular inflow at the level of mitral valve due to structural abnormality of the mitral valve apparatus. The most common cause of mitral stenosis is rheumatic fever. Other less common etiologies include congenital mitral stenosis, malignant carcinoid disease, systemic lupus erythematosus, rheumatoid arthritis, mucopolysaccharidoses of the Hunter-Hurler phenotype, Fabry disease, Whipple disease, and methysergide therapy. The association of atrial septal defect with rheumatic mitral stenosis is called Lutembacher syndrome.

A number of conditions can simulate the physiology of mitral stenosis: severe nonrheumatic mitral annular calcification, infective endocarditis with large vegetation, left atrial myxoma, ball valve thrombus, or cor triatriatum.

Stenosis of the mitral valve typically occurs decades after the episode of acute rheumatic carditis. Acute insult leads to formation of multiple inflammatory foci (Aschoff bodies, perivascular mononuclear infiltrate) in the endocardium and myocardium. Small vegetations along the border of the valves may also be observed. With time, the valve apparatus becomes thickened, calcified, and contracted, and commissural adhesion occurs, ultimately resulting in stenosis.

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.

Pathophysiology

The normal mitral valve orifice area is approximately 4-6 cm2. As the orifice size decreases, the pressure gradient across the mitral valve increases to maintain adequate flow.

Patients will not experience valve-related symptoms until the valve area is 2-2.5 cm2 or less, at which point moderate exercise or tachycardia may result in exertional dyspnea from the increased transmitral gradient and left atrial pressure.

Severe mitral stenosis occurs with a valve area of 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 dyspnea at rest or with minimal exertion. Hemoptysis may occur if the bronchial veins rupture and left atrial dilatation increases the risk for atrial fibrillation and subsequent thromboembolism.

Pulmonary hypertension may develop as a result of (1) retrograde transmission of left atrial pressure, (2) pulmonary arteriolar constriction, (3) interstitial edema, or (4) obliterative changes in the pulmonary vascular bed (intimal hyperplasia and medial hypertrophy). As pulmonary arterial pressure increases, right ventricular dilation and tricuspid regurgitation may develop, leading to elevated jugular venous pressure, liver congestion, ascites, and pedal edema.
Left ventricular end-diastolic pressure and cardiac output are usually normal in the person with isolated mitral stenosis. As the severity of stenosis increases, the cardiac output becomes subnormal at rest and fails to increase during exercise. Approximately one third of patients with rheumatic mitral stenosis have depressed left ventricular systolic function as a result of chronic rheumatic myocarditis. The presence of concomitant mitral regurgitation, systemic hypertension, aortic stenosis, or myocardial infarction can also adversely affect left ventricular function and cardiac output.
Frequency
United States

The prevalence of rheumatic disease in developed nations is steadily declining with an estimated incidence of 1 in 100,000.
International

The prevalence of rheumatic disease is higher in developing nations than in the United States.1 In India, for example, the prevalence is approximately 100-150 cases per 100,000, and in Africa the prevalence is 35 cases per 100,000.
Mortality/Morbidity

Mitral stenosis is a progressive disease consisting of a slow, stable course in the early years followed by an accelerated course later in life. Typically, there is a latent period of 20-40 years from the occurrence of rheumatic fever to the onset of symptoms. Once symptoms develop, it is almost a decade before they become disabling. In some geographic areas, mitral stenosis progresses more rapidly, presumably due to either a more severe rheumatic insult or repeated episodes of rheumatic carditis due to new streptococcal infections, which results in severe symptomatic mitral stenosis in the late teens and early 20s.

In the asymptomatic or minimally symptomatic patient, survival is greater than 80% at 10 years. When limiting symptoms occur, 10-year survival is less than 15% in the patient with untreated mitral stenosis. When severe pulmonary hypertension develops, mean survival is less than 3 years. Most (60%) patients with severe untreated mitral stenosis die of progressive pulmonary or systemic congestion, but others may suffer systemic embolism (20-30%), pulmonary embolism (10%), or infection (1-5%).

Sex

Two thirds of all patients with rheumatic mitral stenosis are female.

Age

The onset of symptoms usually occurs between the third and fourth decade of life.
Clinical
History
Symptoms of mitral stenosis usually manifest during the third or fourth decade of life and nearly half of the patients do not recall a history of acute rheumatic fever.
Patients are generally asymptomatic at rest during the early stage of the disease. However, factors that increase heart rate such as fever, severe anemia, thyrotoxicosis, exercise, excitement, pregnancy, and atrial fibrillation may result in dyspnea.
Nearly 15% of patients develop embolic episodes that are usually associated with atrial fibrillation. Rarely, embolic episodes may occur even in the patient with sinus rhythm. Systemic embolization may lead to stroke, renal failure, or myocardial infarction.
Hoarseness can develop from compression of the left recurrent laryngeal nerve against the pulmonary artery by the enlarged left atrium. Also, compression of bronchi by the enlarged left atrium can cause persistent cough.
Hemoptysis may occur and is usually not fatal.
Pregnant women with mild mitral stenosis may become symptomatic during their second trimester because of the increase in blood volume and cardiac output.
Physical
Presence of mitral facies (pinkish-purple patches on the cheeks) indicate chronic severe mitral stenosis leading to reduced cardiac output and vasoconstriction.
Jugular vein distension may be seen. In the patient with sinus rhythm, a prominent a wave reflects increased right atrial pressure from pulmonary hypertension and right ventricular failure. A prominent v wave is seen with tricuspid regurgitation.
The apical impulse may be laterally displaced or not palpable, especially in cases of severe mitral stenosis. This can be explained by decreased left ventricular filling. Rarely, a diastolic thrill can be felt at the apex with the patient in the left lateral recumbent position.
Often a right ventricular lift is palpable in the left parasternal region in the patient with pulmonary hypertension. A P 2 may be palpable in the 2nd left intercostal space.
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 of the mitral valve, and the duration of the murmur correlates with the severity of the stenosis. The murmur is accentuated by exercise, whereas it decreases with rest and Valsalva maneuver. In patients with sinus rhythm, the murmur increases in intensity during late diastole (so called, presystolic accentuation) due to increased flow across the stenotic mitral valve caused by atrial contraction.
A high-pitched decrescendo diastolic murmur secondary to pulmonary regurgitation (Graham Steell murmur) may be audible at the upper sternal border.
A pansystolic murmur of TR and an S 3 originating from the right ventricle may be audible in the 4th left intercostal space in the patient with right ventricular dilatation.

http://emedicine.medscape.com/article/155724-overview