Friday, March 29, 2024

Congenital Mitral Stenosis

Background

The mitral valve is the inlet valve to the left ventricle (LV). The normal mitral valve is a complex apparatus composed of an annulus and 2 leaflets that are attached by chordae tendineae to 2 papillary muscles. The papillary muscles arise from the walls of the LV and secure the chordae and mitral leaflets, preventing prolapse of the valve during ventricular systole.

Proper function of the mitral valve requires an intact mitral valve apparatus and satisfactory LV function. Mitral stenosis (MS) results from any pathologic process that narrows the effective mitral valve orifice at the supravalvular, valvular, or subvalvular levels. MS can be congenital or acquired.

Congenital MS, a rare entity, takes several forms. These include hypoplasia of the mitral valve annulus, mitral valve commissural fusion, double orifice mitral valve, shortened or thickened chordae tendinae, and parachute mitral valve, in which all chordae attach to a single papillary muscle. The most common associated malformations are coarctation of the aorta, aortic valve stenosis, and subvalvular aortic stenosis. The association of multiple levels of left-sided inflow and outflow tract obstruction is termed the Shone complex.

Severe hypoplasia, or atresia, of the mitral valve results in a hypoplastic LV cavity size that is not capable of sustaining the systemic cardiac output. This situation is considered part of the spectrum of the hypoplastic left heart syndrome and is not considered further in this article. This article deals with MS that, although occasionally severe, allows enough blood flow into the LV to sustain the systemic cardiac output.

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