Mitral valve repair

AORN Journal,  Jan, 2007  by Margo Winters,  Pam Obriot

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The chordae tendineae are attached to the inferior surface of the leaflets. These white, cord-like tendons act only as guides to assist in the coaptation of the two leaflets. The chordae tendineae also prevent the leaflets from billowing or everting up into the atrium. If a primary chordae ruptures, the leaflet everts into the atrium and is called a "flail" leaflet. The chordae are attached to the papillary muscles at the base of the left ventricle.

Oxygenated blood originating from the lungs flows through the pulmonary veins and collects in the left atrium. When pressure in the left atrium is greater than the pressure in the left ventricle, the mitral valve opens allowing blood to flow into the left ventricle. As the intraventricular pressure rises, the mitral valve closes (ie, the leaflets coapt) preventing the backwards flow (ie, regurgitation) of blood into the left atrium. The chordae tendineae guide the leaflets into position; the chordae do not pull the leaflets together. This forms a tight closure (Figure 2), preventing mitral regurgitation and allowing the forward flow of blood through the left ventricular outflow tract, through the aortic valve, and out into the aorta. The function of the mitral valve is regulated by interaction of the components of the mitral apparatus (ie, leaflets, chordae tendineae, papillary muscles, ventricular wall). The mitral apparatus contributes to the normal geometry and function of the left ventricle.

[FIGURE 2 OMITTED]

CAUSES OF MITRAL ABNORMALITIES

Numerous diseases affect the ability of the mitral valve to function properly. Some of these diseases include mitral regurgitation, mitral stenosis, rheumatic heart disease, and cardiomyopathy.

MITRAL REGURGITATION. Mitral regurgitation also is referred to as incompetence or insufficiency. Regurgitation is a result of the leaflets not coming together completely. An incompetent mitral valve allows backflow of blood into the left atrium. This backward flow in turn leads to increased atrial volume and eventually leads to backward flow of blood into the lungs. This backflow into the lungs leads to pulmonary edema. As a result of this blood flow back-up, many patients with mitral regurgitation present to their primary care physician with signs and symptoms of right heart failure. (2) The heart works harder to try to compensate for the lost forward blood flow; the ventricles may begin to hypertrophy (ie, thicken) because of the added workload. If there is an ischemic area in the left ventricle from a myocardial infarction, the tissue can weaken and become stretched, forming an aneurysm, and become dysfunctional.

MITRAL STENOSIS. Mitral stenosis refers to the calcification of the leaflet and annulus. A stenotic mitral valve also leads to heart failure in much the same way as mitral regurgitation, but instead of blood moving backwards through the mitral valve, mitral stenosis does not allow enough blood through the narrowed, fused, or calcified opening of the mitral valve leaflets. The process continues much the same as is seen in mitral regurgitation, resulting in right heart failure as blood volume builds up in the lungs. Stenotic valve repair is more complicated than repair of a dilated mitral annulus and requires more experience on the part of the surgeon (5) The surgeon must make decisions about excising calcified valvular tissue and possibly replacing chordae or advancing leaflets. Each patient's valve is different regarding the degree of stenosis and involvement of the chordae tendineae and papillary muscles.