Most notable are a loud S|; an opening snap early in diastole, followed by a diastolic murmur which is mostly decrescendo. By phonocardiogram, the murmur actually has two brief crescendo periods, the first just after the opening snap, and the second with atrial contraction. These periods of crescendo murmur correspond to the two periods of the greatest transvalular gradient in diastole.
Why is the first heart sound (S,) accentuated?
The explanation for this is uncertain. McCall and others have suggested that the mitral valve leaflets must be pliable for the S; to be accentuated. The accentuated Sj then is caused in part by the rapidity of the upstroke of the left ventricular pressure at the time of mitral valve closure. In addition, the wide excursion or displacement of the mitral valve leaflets prior to closure is felt to play a role in the accentuated S,. Marked calcification or thickening of the mitral valve reduces the amplitude of S,. Finally, the presystolic accentuation of mitral blood flow caused by atrial contraction blends into S[ and may contribute to the perceived accentuation.
What are the hemodynamic findings in mitral stenosis?
The most important finding is the presence of a pressure gradient across the mitral valve. That is, during diastole, the pressure in the left atrium is greater than the pressure in the left ventricle. This gradient is measured by recording the left ventricular diastolic pressure simultaneously with the pulmonary capillary wedge pressure (PAW). The PAW is used as a close approximation of the left atrial pressure. The mean gradient across the mitral valve can then be determined, and with the Gorlin formula, the valve area (in cm2) can be calculated:
Cardiac output/(heart rate x avg. diastolic period)
Describe the echocardiographic findings in mitral stenosis.
M-mode echocardiography. The most specific finding by M-mode echocardiography is the posterior mitral valve leaflet moving in an anterior direction with the anterior mitral valve leaflet in diastole. This demonstrates the tethering of the valve leaflets caused by fusion of the commissures (Fig. 1). Other, less specific findings include increased echoes from the mitral valve due to thickening and/or calcification, and decreased E-F slope due to low flow across the mitral valve (Fig. 1). Decreased E-F slope is a frequent finding in severe heart failure and could be confused with mitral stenosis in this setting.
Two-dimensional echocardiography. The findings of mitral stenosis include diastolic bowing (“hockey stick” formation) of the anterior mitral leaflet (Fig. 2), thickening and increased echogenicity of the mitral valve leaflets, annulus, and subvalvular apparatus, and narrowed orifice of the valve as measured by short axis. The actual valve area can be measured by 2-dimensional echocardiography in the short-axis view (Fig. 3).
Doppler echocardiography. Findings in mitral stenosis include an elevated velocity across the mitral valve (1.3 m/s or 130 cm/s), indicating an abnormally high transvalvular gradient, and prolonged pressure half-time.