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.