Ventricular Outflow Tract Obstruction in the Adult
The classic initial septal resection is begun by making a longitudinal incision at the nadir of the right coronary cusp and extending this in a counter-clockwise manner toward the mitral valve (Fig. 14.1). Importantly, muscular resection between the nadir of the right coronary cusp and the commissure between the left and the right cusps is anatomically the ventricular septum. Muscular resection (Fig. 14.2) of the commissure between the left and right cusps and the anterior leaflet of the mitral valve is carried out toward the posterolateral free wall of the left ventricle. Resection along the posterolateral free wall is determined by the thickness of the posterior wall, as noted on the echocardiogram. Figure 14.3 shows a transaortic view of the initial large segment excision of the basal septum. Figure 14.4 demonstrates a coronal view of the initial segmental resection of the hypertrophied septum. The myectomy is then extended in a more apical fashion toward the bases of the papillary muscles. It is essential that the muscular resection extend well below the area of mitral septal contact that is usually marked by a fibrous friction lesion (Fig. 14.5). The classic resection is extended in several ways, beginning with continued resection leftward toward the mitral valve annulus and apically to the bases of the papillary muscles (Fig. 14.6). Resection from the apical third of the right side of the septum is also performed, effectively making a much wider trough at the apex than at the base, as noted in the coronal view in Fig. 14.7.
For mid ventricular obstruction owing to hypertrophy, bulky papillary muscles, or additional muscle bundles, additional resection is made around the bases of the papillary muscles; in some situations, the sides of the papillary muscles are also shaved (Fig. 14.8). All areas of papillary muscle fusion to the ventricular septum or the ventricular free wall are divided, including anomalous chordal structures with fibrous attachments between the side of the mitral leaflet and the ventricular septum. This division allows full mobility of the papillary muscles so they can move out of the outflow tract during systole. The resected area is carefully deepened with a rongeur. The adequacy and distal extent of the resection are evaluated by direct inspection and digital palpation.
The most common reason for residual gradients is inadequate septectomy at the mid ventricular level. In general, the resection is complete when one can visualize the bases of the papillary muscles while looking through the aortic root after completion of the myectomy. The left ventricle is irrigated to remove any particular debris, and the aortic and mitral valves are inspected to ensure that there has been no injury. After the patient is weaned from cardiopulmonary bypass, pressures in the left ventricle and the aorta are measured again, and TEE evaluation is repeated. Transesophageal echocardiography can quantify and localize any residual gradient and exclude an iatrogenic ventricular septal defect (VSD). If successful myectomy has been performed, there is little or no residual gradient and little or no SAM of the anterior leaflet. If isoproterenol provocation was required before the myectomy, then it is repeated after the myectomy to ensure that the gradient is abolished. In general, we would resume bypass for further resection if the gradient is greater than 15–20 mmHg or if there is SAM of the anterior leaflet of the mitral valve. Transthoracic echocardiography is performed prior to hospital discharge.
14.1.2 Middle Ventricular Resection Via Apical Left Ventriculotomy
Exposure to mid ventricular obstruction (at the bases of the papillary muscles) almost always requires an apical ventriculotomy of the left ventricle. Standard aortic and right atrial cannulation is performed as described above. As with the transaortic approach, cold blood antegrade cardioplegia with aortic occlusion is used. After satisfactory asystolic arrest, the apex of the left ventricle is brought into the operative field by placing multiple sponges behind the heart (Fig. 14.9).
The ventriculotomy is performed by making an incision 1.5–2 cm parallel and lateral to the left anterior descending coronary artery. The apical ventricular incision is approximately 1.5–2 cm in length; two thirds of the incision is on the anterior wall of the left ventricle, and one third is on the posterior wall. Rake retractors are placed. The first step is to inspect the anatomy of the papillary muscles, which are often apically displaced and can be very close to the ventriculotomy. Figure 14.10 shows a coronal view of the left ventricle with a portion of the ventricle removed to characterize the internal left ventricular anatomical components. The septal bulge is noted, with its relationship to the hypertrophied papillary muscles.
A rigid suction catheter is placed through the left ventriculotomy, and the papillary muscles and anterior leaflet of the mitral valve are retracted leftward, away from the ventricular septum. Inspection demonstrates a typical friction lesion at the point of contact between the hypertrophied papillary musclesand the hypertrophied ventricular septum. This provides a useful landmark to guide the initial area of resection, as noted in Fig. 14.11. A hook retractor is placed into the hypertrophic septal muscle at the level of the friction lesion, and a substantial septal resection is performed to the surgeon’s side of the table (right side). The depth of the resection is determined by the overall thickness of the ventricular septum. The septum is typically quite thick at this juncture, so a generous muscle resection usually can be performed. After septal resection, the posterolateral and anterolateral free walls are inspected, including close evaluation of the thickened papillary muscles. The sides of the papillary muscles are carefully shaved, creating additional space in the mid ventricularcavity (Fig. 14.12). Areas of the anterolateral and posterolateral free walls of the left ventricle can also undergo muscle resection, depending on the degree of hypertrophy in these areas. The most essential part of the operation is ensuring that there is no iatrogenic injury to the mitral valve. It is important to perform very little myectomy at the edges of the ventriculotomy site, so that closure can be performed safely with an area of thickened muscle, to avoid formation of a potential aneurysm in the future. After the septal free wall and papillary muscle resections, the left ventricular cavity is irrigated with saline solution to remove any debris. The ventriculotomy is then closed with running “over-and-over” propylene suture in two layers over felt strips (Fig. 14.13). Air is evacuated through the aortic root, and the cross-clamp is released in the usual manner. Similar to thetransaortic approach, post-cardiopulmonary bypass TEE is performed to confirm the absence of a mid ventricular gradient, and direct pressure measurements with exploring needles in the left ventricular cavity and ascending aorta are repeated.
Occasionally, muscle resection from the apexalone can result in a residual shelf of muscle toward the base of the heart that is not easily reached from the apex. In this situation, systolic anterior motion of the mitral valve may be present after mid ventricular resection. This ledge can be resected typically via aortotomy after resuming cardiopulmonary bypass with a second period of aortic occlusion; in our experience, additional resection is usually not necessary, and it is best to use TEE to determine.
14.1.3 Success of Septal Myectomy Procedures for Left Ventricular Outflow Obstruction
Septal myectomy effectively and definitively relieves left ventricular outflow tract obstruction and cardiac symptoms in adults and children with obstructive hypertrophic cardiomyopathy. In experienced centers, early mortality for isolated myectomy is less than 1%, and overall results are excellent and continue to improve. Late recurrence of significant resting left ventricular outflow tract obstruction is very uncommon after successful myectomy and complete elimination of the gradient in the setting of obstructive hypertrophic cardiomyopathy. Causes of recurrent left ventricular outflow obstruction and symptoms include inadequate myectomy at the first operation, mid ventricular obstruction, and anomalies of the mitral valve and papillary muscles. Most often, inadequate myectomy at the initial operation is the result of failure to extend the myectomy far enough toward the mid ventricle and apex of the heart. The myectomy trough should be wider at the mid ventricular portion and should mirror the anterior leaflet, chordae, and papillary muscles. Despite excellent early and late results, lifelong medical surveillance is essential.
14.2 Aortic Valvotomy for Stenotic Bicuspid Valve
The most common form of congenital aortic valvar stenosisis the result of a fused bicuspid aortic valve. If the valve is not stenotic, patients can be observed for decades, but they often require aortic valve replacement in their fifth decade, owing to accelerated calcification. If the valvar stenosis is hemodynamically significant in infancy or childhood, the current standard of care in most centers calls for transcatheter balloon dilatation, which results in inaccurate valvar tearing that may be associated with neoaortic regurgitation. Because of the long-term results of stenosis or regurgitation, there is new interest in surgical intervention that can effect exact commissurotomy and resection of hypertrophied leaflet nodules. More long-term experience is necessary to resolve this issue. In any case, adult patients presenting with congenital aortic stenosis owing to a bicuspid valve generally have undergone at least one intervention such as balloon dilatation or palliative operations. Balloon dilatation often lessens the stenosis but can cause important aortic regurgitation. Previous operations include aortic valvotomy, Ross or Ross-Konno operations, and the many forms of left ventricular outflow tract relief, each one with its own set of potential complications that leave the patient with stenosis, regurgitation, or—in most cases—both.
It is rare for an adult patient who has undergone remote balloon dilatation without regurgitation to present for further treatment. For the patients who do need treatment, no therapeutic intervention is considered curative, so the surgeon and the patient must consider the best approach for the short term and long term. Surgical valvotomy in the adult, though rarely indicated, can be used for those patients whose aortic valve is well-formed and can be amenable to conservative techniques of valvotomy, valvar shaving, and repair of the balloon-induced tears likely to have been caused by transcatheter techniques. Figure 14.14 shows the operative approach for aortic valve commissurotomy. Aortobicaval cardiopulmonary bypass is established, with aortic cross-clamping and antegrade/retrograde cardioplegic arrest (not shown). The dotted line shows the area of the transverse aortotomy that allows optimal exposure. Figure 14.15 shows the bicuspid aortic valve and the coronary artery sinuses. Oftentimes, a forme fruste of a nonsupportive commissure is noted in the larger of the two sinuses of Valsalva. Figure 14.16 depicts accurate commissurotomy being performed with a sharp scalpel and forceps stabilization of the affected commissure. Once the commissurotomies are performed, the aorta can be closed (Fig. 14.17), air maneuvers accomplished, and the cross-clamp can be removed. The results of such an operation are dependent on the underlying anatomical valvar structure. Bicuspid valves are more amenable to this approach than unicuspid valves. In most long-term series, patients undergoing this operation have required subsequent operations, although it is durable for the most part. The adage that congenital aortic stenosis is a lifelong problem with therapeutic interventions that are largely palliative in nature is mostly accurate.
14.3 Repair of Aortic Regurgitation Associated with Juxta-Arterial or Doubly Committed Ventricular Septal Defect
Juxta-arterial and doubly committed VSDs, also known as subarterial, Type I, and supracristal defects, can be associated with important aortic regurgitation owing to prolapse of aortic leaflets into the VSD. The anatomy is highlighted by a shared annulus between the aorta and the pulmonary artery, with the right coronary cusp prolapsing into the VSD. The prolapse is caused by the accelerated left to right flow through the VSD, which results in a Venturi effect on the aortic leaflet that causes it to stretch, prolapse, and pull away from its coapting physioanatomic relationship with the other leaflets. This condition is progressive and results in increasing aortic regurgitation, hemodynamic aberrations, and endocarditis in some patients, so it is ideal to repair the VSD before aortic regurgitation occurs. When patients present with aortic regurgitation, a Trussler aortic leaflet reefing procedure can be accomplished with excellent and lasting results. The details of this operation are found in Chap. 6.
14.4 Aortic Leaflet Extension with Pericardial Patches for Aortic Regurgitation
Aortic leaflet extension to repair stenotic andregurgitant aortic valves has been performed with various leaflet extension materials, such as glutaraldehyde-treated autologous pericardium, thin-walled polytetrafluoroethylene (PTFE) membrane material, and biologic materials. These leaflets tend to fail over time, owing to calcification, fibrosis, retraction, and disintegration. The intent of the operation in most cases has been to repair the valve as a palliative procedure; future options that can be used when the patient is older and more mature include insertion of a bioprosthetic or mechanical valve or the Ross operation. Figure 14.18 shows the initial approach for leaflet extension using glutaraldehyde-treated autologous pericardium after aortobicaval cardiopulmonary bypass, aortic cross-clamping, left ventricular venting, and aortic exposure. The pericardium is trimmed in a crescent shape; the suture line for the extension is started at the center of the valve leaflet (Fig. 14.18) and extended toward the commissure (Fig. 14.19). The corresponding side is also attached to the remainder of the leaflet (Fig. 14.20). In a similar fashion, another pericardial patch is configured and used to extend the remaining aortic leaflet (Fig. 14.21). The neocommissures are then attached to the aortic wall using pledgeted sutures, as demonstrated in Fig. 14.22 and shown completed in Fig. 14.23. Pericardial patch aortic leaflet extension usually functions well in the immediate postoperative period and in most cases lasts 2–5 years, depending on the complexity of the initial repair and the patient’s reaction to the material used. (This operation may become more attractive in the future if more durable bioprosthetic material is developed.) It is most important that leaflet extension does not preclude an eventual Ross operation.