Figure 15.3 shows a lateral coronal v iew of supravalvar mitral stenosis. The plane between the supravalvar ring and the mitral orifice has been exaggerated to highlight the anatomic relationship. Generally, these patients have longstanding mitral stenosis and a large left atrium; this makes the approach through the interatrial groove preferable. The key to proper exposure is to employ a large left atrial incision with traction annular sutures to bring the annulus into the operative field for the membrane excision (Fig. 15.4). A Beaver blade (Fig. 15.5) is employed to find the dissection plane between the fibrous ring and the annulus using endarterectomy techniques. The dissection plane can be developed much like removal (i.e., enucleation) of a subvalvar aortic ridge. Careful and deliberate dissection effectively removes the fibrous ring without injury to the underlying mitral annulus. With complete excision of the ring, the restricted motion of the leaflets is alleviated, resulting in a much larger mitral orifice (Fig. 15.6). The mitral valve can then be tested for competence with a cold saline injection into the left ventricle. The atrium is closed with proper deairing of the left side of the heart, and the cross clamp is removed. After separation from cardiopulmonary bypass, transesophageal echocardiography is used for valve analysis. Occasionally, the mitral valve ring is situated within the body of the mitral valve, as shown in Fig. 15.7. Under these circumstances, the valve is approached and exposed in the same manner as for supravalvar stenosis. The dissection plane is developed using endarterectomy techniques, and the fibrous ring is carefully dissected from the surrounding valvar tissue with special care taken not to injure the underlying valve. In the event that unwanted mitral leaflet perforation complicates the excision, a piece of bovine pericardium can be used to repair the leaflet perforation. Ordinarily, the orifice of the mitral valve can be enlarged significantly. When the subvalvar papillary muscle structure is also stenotic, carefully calculated papillary muscle incisions between the chordae can be accomplished to allow further mobility of the leaflets and to maximize inflow to the body of the left ventricle (Fig. 15.7).

Double orifice mitral valve is an anatomic abnormality in which there are two reasonably formed inlets into the left ventricle. Figure 15.8 shows a left atrial superior view of the double orifice mitral valve. Figure 15.9 shows the same atrioventricular valve in a coronal view. Typically, the smaller of the two orifices is rightward, while the larger orifice is leftward as seen by the surgeon across from the left atrium. The degree of stenosis is variable, and effective orifice enlarging operations have not been reported. The most important tenet when approaching this valve is not to cut the isthmus between the two orifices. This results in severe regurgitation that cannot be repaired because of a lack of subtended supporting chordae tendineae in the middle of the valve. The best approach to a stenotic double orifice valve is to look for and treat any secondary causes of stenosis such as papillary muscle obstructive lesions. Sometimes a cleft is present in the anterior leaflet of the larger orifice. Experience and judgment determine whether the cleft should be closed, depending on the amount of resultant stenosis if the cleft is closed or the amount of regurgitation if the cleft is left unrepaired.

When mitral valve stenosis and annular hypoplasia are associated with an inadequately sized left ventricle, the patient is generally treated along the single ventricle pathway en route to a Fontan circulation. A hypoplastic valve and annulus can occasionally be associated with a functionally adequately sized left ventricle, especially if a ventricular septal defect is present. The hypoplastic valve may appear to be quite similar to a normal mitral valve in so far as there are two leaflets with corresponding chordae tendineae that appear appropriate. The leaflets are generally mobile with nonfused commissures. Alternatively, the leaflets are thickened, and the commissures are fused. These valves can be associated with thickened, short, and inadequate chordae tendineae with poorly developed interchordal spaces. If the chordae are shortened, a funnel-like appearance may be seen. Most often these characteristics match up very well with what most anatomists call an arcade mitral valve. The anterior and posterior groups of papillary muscles join together and fuse with the entire leading edge of the leaflet without the presence of well-formed chordae. Only one papillary muscle may participate in the arcade in some cases. The arcade mitral configuration can produce mitral stenosis or regurgitation or a mixed lesion. It may also be associated with a parachute valve. In general, therapy is aimed at incising the elongated and narrowed papillary muscle that is responsible for the central obstructing orifice and making fenestrations in the existing valve leaflets. Figure 15.10 shows a coronal atrioventricular view, and Figs. 15.11 and 15.12 show atrial views of a stenotic parachute valve that has similar anatomic characteristics to an Arcade/Hammock mitral valve and is discussed below in the section on Parachute Mitral Valve. Once the appropriate incisions and fenestrations are performed, the valve orifice can be measured with dilators. The predictive adequacy of the valvuloplasty can be evaluated by comparing it with standard measurements of normal mitral valves for somatic size. The mitral valve competence can be assessed with a saline-filled bulb syringe. The most important advice and technical pearls one surgeon can give to another is to “establish excellent exposure with retraction sutures in the annulus, measure ten times, and cut once.” Incision into the papillary muscle must be made accurately, deliberately, and centrally to avoid papillary muscle avulsion and to maintain chordal attachments.