A median sternotomy approach is used. Surgical valvotomy is performed on cardiopulmonary bypass. Cannulation is carried out with a standard aortic cannula and a single venous cannula in the right atrial appendage. Cardiopulmonary bypass is begun, and the ductus arteriosus is closed with a heavy tie or metal clip. The aorta is cross-clamped, and cardioplegic solution is administered (see Chapter 3). The aorta is incised transversely, the aortic valve is exposed, and its anatomy is studied closely. A no. 15 blade is used to incise the fused commissures to within 2 mm of the aortic annulus (Fig. 24-1).

A myotomy or a limited myectomy involving the bulging septum is recommended to prevent the possible persistence of a significant residual obstruction (Fig. 24-3C). This may also help to prevent recurrence of the membrane, the incidence of which is higher the younger the patient is when the initial surgery is performed.

A substantial segment of the abnormal fibromuscular tissue can be excised and removed from the septal area without producing a defect in the interventricular septum. If such a complication does occur, the defect must be identified and closed. Pledgeted sutures are essential to protect the friable muscular tissue.

Only the white fibrous tissue should be mobilized and removed from the area immediately below the rightward half of the right cusp and the commissure between the right and noncoronary cusps. Otherwise, the conduction tissue may be injured resulting in heart block (Fig. 24-3B).

Occasionally, the membranous tissue is adherent to the underside of the right coronary leaflet of the aortic valve. It must then be meticulously dissected free without damaging the aortic valve to avoid producing valvular insufficiency.

Occasionally, the lesion may extend and become adherent to the anterior leaflet of the mitral valve; in this case, it should be dissected free with the utmost care. Injury to the mitral valve near its annulus may result in an opening into the left atrium.

Most surgeons use a transaortic approach. Exposure is facilitated by extending the aortotomy obliquely down to the noncoronary annulus and placing plegeted sutures just above the valve commissures. By placing traction on these sutures, the hypertrophied septum can be visualized. After the initial wedge resection, a small rake retractor can be placed into the septum and pulled upwards toward the aortic annulus to allow visualization and resection of the apical portion of the septum.

When systolic anterior motion of the anterior leaflet of the mitral valve is a significant component of the
left ventricular outflow tract obstruction, an adequate septal myectomy usually resolves the abnormal motion of the anterior leaflet and any mitral regurgitation. However, some patients have associated abnormalities of the mitral subvalvular apparatus, which must be recognized and treated at the time of surgery. These include anomalous papillary muscle insertion directly into the anterior leaflet of the mitral valve and abnormal chordae tendineae attaching to the ventricular septum. If present, the abnormal chords are resected, and any areas of fusion of the papillary muscle(s) to the septum or free wall are divided. Occasionally, a valvuloplasty procedure to shift the coaptation level of the valve posteriorly may be required. This may involve anterior and/or posterior leaflet plication usually combined with an annuloplasty. A simple technique that may be effective is an Alfieri stitch placed 1 cm away from the free edges connecting the central portion of the anterior and posterior leaflets (see Chapter 6). Rarely, the mitral valve must be replaced with a low-profile prosthesis, resecting the entire anterior subvalvular apparatus. When combined with a myectomy, these techniques result in relief of the obstruction.

All anomalous chords attached to the free edge of the anterior leaflet must be preserved to prevent a flail leaflet.

During the process of excising the hypertrophied muscle, fragments may fall into the left ventricular cavity, resulting in a subsequent embolism. This can be prevented to some degree by pulling on the desired segment to be excised with a 4- 0 or 5-0 Prolene stitch (Fig. 24-4). A biopsy forceps may be used to resect muscle from the more apical portions of the septum. Care should be taken to remove all debris from within the left ventricular cavity.

Exposure may be inadequate through the retracted aortic leaflets. The obstructing muscle may then be removed through a left atriotomy working through the mitral valve.

Recently, a catheter technique that injects pure alcohol into a septal perforator artery has been used successfully to produce an infarction of the septum and lower the gradient across the left ventricular outflow tract. The role of this procedure needs to be further delineated.

Bicaval and aortic cannulations are made in the usual manner. On cardiopulmonary bypass with moderate cooling, the aorta is cross-clamped and cardioplegic arrest of the heart is achieved by the usual techniques (see Chapter 3). The aorta is incised anteriorly in a longitudinal direction. The incision is then extended downward under direct vision into the root of the aorta.