Chapter 31

Mitral Stenosis, Mitral Regurgitation, and Mitral Valve Prolapse

1. What is the usual cause of mitral stenosis (MS)?

Most cases of MS stem from previous episodes of rheumatic fever. Most cases of rheumatic heart disease are seen in patients who emigrate from areas of the world where rheumatic fever is still common, including the Middle East, Asia, and South Africa. Although the rate of rheumatic fever is similar in men and women, MS is three times more common in women than in men. However, as the population ages, mitral annular calcification is increasing as an etiology for MS.

2. What is the pathophysiology of MS?

MS inhibits the normal free flow of blood from left atrium (LA) to left ventricle (LV) in diastole. Normally, diastolic LA and LV pressures equalize shortly after mitral valve opening. In MS, the stenotic valve impedes LA emptying, inducing a diastolic gradient between LA and LV (Fig. 31-1). Elevated LA pressure is referred to the lungs, where it causes pulmonary congestion. Simultaneously, impaired LA emptying reduces LV filling, limiting cardiac output. Thus, the combination of increased LA pressure and decreased cardiac output produce the syndrome of heart failure. Because increased LA pressure increases pulmonary pressure, the right ventricle (RV) becomes pressure overloaded, eventually leading to RV failure.

Figure 31-1 Pressure gradient in a patient with mitral stenosis. The pressure in the left atrium (LA) exceeds the pressure in the left ventricle (LV) during diastole, producing a diastolic pressure gradient (shaded area). (Modified from Bashore TM: Invasive cardiology: principles and techniques, Philadelphia, 1990, BC Decker, p. 264.) ECG, Electrocardiogram.

3. What are the typical symptoms of MS?

Patients with mild disease are likely to be asymptomatic. As MS worsens, dyspnea appears, as does orthopnea and paroxysmal nocturnal dyspnea. If RV failure ensues, it may be accompanied by edema and ascites. During exercise, sudden increases in LA pressure and pulmonary venous pressure may cause rupture of anastomoses between pulmonary and systemic veins, leading to hemoptysis.

4. What are the signs of MS at physical examination?

The gradient across the mitral valve holds the valve open throughout diastole, so that when it closes, S1 may be quite loud. The murmur of MS is a soft diastolic rumble heard near the apex. The murmur is often preceded by an opening snap, caused by sudden opening of the stiffened mitral valve from higher than normal atrial pressure. If pulmonary hypertension has developed, P2 is increased in intensity. If RV failure has occurred, elevated neck veins, ascites, and edema are likely to be present.

5. How is the diagnosis of MS made?

The chest radiograph used to be at the forefront of diagnosis and still can be helpful today. It demonstrates an enlarged LA, seen as a double shadow along the right-sided heart border. Thickened lymphatics from high pulmonary venous pressure are seen as Kerley lines. The pulmonary artery (PA) is usually enlarged.

Today, however, the echocardiogram is key to the diagnosis because it images the mitral valve so well. The valve is thickened and there is impaired opening of the mitral leaflets (Fig. 31-2). The LA is almost always enlarged. Valve area can be determined from direct visualization and planimetry of the mitral orifice, from Doppler assessment of the transvalvular gradient, and from measuring the delay in LA emptying. Pulmonary pressure, LV function, and RV function are also evaluated. In general, the main criteria for severe MS follow below. The severity of MS is estimated using the criteria given in Table 31-1.

TABLE 31-1

ECHOCARDIOGRAPHIC CRITERIA FOR THE ASSESSMENT OF THE SEVERITY OF MITRAL STENOSIS

PA, Pulmonary artery.

Modified from Bonow RO, Carabello BA, Chatterjee K, et al: ACC/AHA 2006 guidelines for the management of patients with valvular heart disease. J Amer Coll Cardiol 48:e1-e148, 2006.