Mitral Stenosis

Essentials of Diagnosis

  • Dyspnea, orthopnea, and paroxysmal nocturnal dyspnea.
  • Symptoms often precipitated by onset of Atrial fibrillation or pregnancy.
  • Prominent mitral first sound, opening snap (usually), and apical diastolic crescendo rumble.
  • ECG shows left atrial abnormality and, commonly, atrial fibrillation. Echo-Doppler confirms diagnosis and quantitates severity.

General Considerations
Nearly all patients with mitral stenosis have underlying rheumatic Heart disease, though a history of rheumatic fever is often absent.

Clinical Findings
A. Symptoms and Signs
A characteristic finding of mitral stenosis is a localized middiastolic murmur low in pitch whose duration varies with the severity of the stenosis and the heart rate (Table 10-1). Because it is thickened, the valve opens in early diastole with an opening snap. The sound is sharp, is widely distributed over the chest, and occurs early after A2 in severe and later in milder varieties of mitral stenosis. In severe mitral stenosis with low flow across the mitral valve, the murmur may be soft and difficult to find, but the opening snap can usually be heard. If the patient has both mitral stenosis and mitral regurgitation, the dominant features may be the systolic murmur of mitral regurgitation with or without a short diastolic murmur and a delayed opening snap.

When the valve has narrowed to less than 1.5 cm2 (normal, 4-6 cm2), the left atrial pressure must rise to maintain normal flow across the valve and a normal cardiac output. This results in a pressure difference between the left atrium and left ventricle during diastole. The pressure gradient and the length of the diastolic murmur reflect the severity of mitral stenosis; they persist throughout diastole when the lesion is severe or when the ventricular rate is rapid.

In mild cases, left atrial pressure and cardiac output may be essentially normal and the patient asymptomatic, but in moderate stenosis (valve area < 1.5 cm2) - especially with tachycardia, which shortens diastole and increases mitral flow rate - dyspnea and fatigue appear as the left atrial pressure rises. With severe stenosis, the left atrial pressure is high enough to produce pulmonary venous congestion at rest and reduce cardiac output, with resulting dyspnea, fatigue, and right heart failure. Recumbency at night further increases the pulmonary blood volume, causing orthopnea and paroxysmal nocturnal dyspnea. Severe pulmonary congestion may also be initiated by any acute respiratory infection, excessive salt and fluid intake, endocarditis, or recurrence of rheumatic carditis. As a result of long-standing pulmonary venous hypertension, anastomoses develop between the pulmonary and bronchial veins in the form of bronchial submucosal varices. These often rupture, producing mild or severe hemoptysis. In a few patients, the pulmonary arterioles become narrowed; this greatly increases the pulmonary artery pressure and accelerates the development of right ventricular hypertrophy and failure. These patients have relatively little dyspnea but experience fatigue on exertion.

Fifty to 80 percent of patients develop paroxysmal or chronic atrial fibrillation that, until the ventricular rate is controlled, may precipitate dyspnea or pulmonary edema.

B. Diagnostic Studies
Echocardiography is the most valuable technique for assessing mitral stenosis. The valve is thickened, opens poorly, and closes slowly. The anterior and posterior leaflets are fixed and move together, rather than in opposite directions. Left atrial size can be determined by echocardiography: increased size denotes an increased likelihood of atrial fibrillation or systemic emboli. The mitral valve area can be measured, and the gradient and pulmonary artery pressure can be estimated by Doppler techniques. Echocardiography also detects atrial myxoma, which sometimes presents clinically in a fashion resembling mitral stenosis.

Because echocardiography and careful symptom evaluation provide most of the needed information, cardiac catheterization is employed primarily to detect associated valve, coronary, or myocardial disease - usually after the decision to intervene has been made.

Treatment & Prognosis
Mitral stenosis may be present for a lifetime with few or no symptoms, or it may become severe in a few years. In most cases, there is a long asymptomatic phase, followed by subtle limitation of activity. Pregnancy and its associated increase in cardiac output and the transmitral pressure gradient often precipitate symptoms. The onset of atrial fibrillation often precipitates more severe symptoms, which usually improve with control of the ventricular rate or restoration of sinus rhythm. Conversion to and subsequent maintenance of sinus rhythm is most commonly successful when the duration of atrial fibrillation is brief (< 6-12 months) and the left atrium is not severely dilated (diameter < 4.5 cm). Once atrial fibrillation occurs, the patient should receive warfarin anticoagulation therapy even if sinus rhythm is restored, since atrial fibrillation often recurs even with antiarrhythmic therapy and 20-30% of these patients will have systemic embolization if untreated. Systemic embolization in the presence of only mild to moderate disease is not an indication for surgery but should be treated with warfarin anticoagulation.

Indications for relieving the stenosis include the following: (1) uncontrollable pulmonary edema, (2) limiting dyspnea and intermittent pulmonary edema, (3) evidence of pulmonary hypertension with right ventricular hypertrophy or hemoptysis, (4) limitation of activity despite ventricular rate control and medical therapy, and (5) recurrent systemic emboli despite anticoagulation with moderate or severe stenosis.

Open mitral commissurotomy may be effective in patients without substantial mitral regurgitation. Replacement of the valve is indicated when combined stenosis and insufficiency are present or when the mitral valve is so distorted and calcified that a satisfactory valvulotomy is not possible. Operative mortality rates are low: 1-3% in most institutions. Balloon valvuloplasty is effective in patients without accompanying regurgitation. Initial success rates are high, especially if valve calcification is not excessive. The rate of restenosis is lower than that with aortic stenosis. As a result, this option appears to be a suitable alternative to surgery for many patients in experienced centers.

Problems associated with prosthetic valves are thrombosis (especially at the mitral position), paravalvular leak, endocarditis, and degenerative changes in tissue valves. Warfarin anticoagulant therapy is mandatory with mechanical prostheses and is usually employed for at least the initial 3 months with bioprostheses, especially if the patient has significant left atrial enlargement. If atrial fibrillation persists postoperatively, ongoing anticoagulation is required.

Rahimtoola SH: Current evaluation and management of patients with mitral stenosis. Circulation 2002;106;1183.
Vahanian A: Balloon valvuloplasty. Heart 2001;85:223.

Provided by ArmMed Media
Revision date: July 8, 2011
Last revised: by Andrew G. Epstein, M.D.