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A small aortic root is a challenging problem in congenital heart surgery, commonly seen in children with tri-leaflet, and occasionally bileaflet, aortic valve stenosis. Mixed aortic stenosis and regurgitation may be present, especially in patients who have previously undergone surgical or interventional procedures to relieve aortic stenosis. When long standing aortic regurgitation is present, however, a larger aortic annulus is more likely.
Prosthetic valves smaller than 17 mm in diameter are rarely manufactured since the effective orifice area of these valves would leave a substantial gradient. Because of the mathematical relationship (A = πr2), even a small decrease in the radius of the valve leads to a substantial decrease in the cross-sectional area. Furthermore, the use of small prosthetic valves may produce prosthesis-patient mismatch, resulting in complications such as persisting left ventricular dysfunction or hypertrophy, hemolysis, and thrombosis.
Choosing a marginally sized prothesis has particularly far reaching consequences in children, who may have the potential for substantial further growth.
Management of the small aortic annulus initially involved bypassing the obstructive outflow tract using a conduit from the apex of the left ventricle to the descending aorta. This approach was supplanted by the three currently accepted alternative solutions: (1) Use of stentless tissue prosthesis, (2) enlargement of the aortic annulus, and (3) implantation of an adequate sized prosthesis in a tilted supra-annular position. In children, tissue valves are a poor choice because of their limited lifespan. Placement of a prosthesis in the tilted supra-annular position is likely to result in use of only a single size larger prosthesis than might be expected utilizing standard annular positioning. This is often inadequate when growth considerations are taken into account. Formal annular enlargement is, therefore, often the procedure of choice in young patients. The relatively recent introduction of the use of the pulmonary autograft to reconstruct the left ventricular outflow tract in children has had a major impact on the decision making process in young patients with aortic stenosis and small aortic root, and the autograft implantation may be combined with any of the various techniques of root enlargement. There are times, however, when the autograft is either contraindicated, or not preferred for a variety of reasons. In these cases, aortic root enlargement is combined with placement of a mechanical prosthesis.
Historically, posterior annular enlargement was the first of these techniques reported by Nicks and colleagues
in 1970. They proposed patch enlargement of the aortic annulus by extending the incision through the mid-portion of the noncoronary sinus through the aortic annulus. Subsequently, an alternative procedure was described whereby posterior annular enlargement is achieved by extending an oblique incision toward the commissure of the left coronary and noncoronary cusps, mitral annulus, and anterior mitral leaflet (AML) at it's midpoint, followed by reconstruction of this defect using a diamond shaped patch.
most have come to recognize the procedure as the “Maouguian.” At about the same time, Konno and colleagues described anterior annular enlargement by longitudinal incision of the aortic root along the commissure of the right and left coronary cusp with an extension onto the septum and the outflow tract of the right ventricle.
With the Nicks procedure, the incision can not be easily directed to the center of the AML and, hence, can not be extended across the mitral annulus, lest it cause leaflet distortion and resultant mitral regurgitation. In contrast, by means of the Manouguian procedure, not only the mitral leaflet, but also the left atrial attachment at the base of the aorta can be divided. Therefore, while with the Nick's procedure one is generally limited to a one-size larger prosthesis, with the Manouguian incision one can insert a two-size larger prosthetic valve.
Often the small root presents in the context of multiple obstructive lesions involving the left side of the heart. Our preference for management of a small aortic root in a child with tunnel obstruction of the left ventricular outflow tract is the Konno procedure, since this would allow an opportunity to address not only the small root but also the accompanying subvalvar stenosis. Similarly, a Konno procedure is preferred when it is expected that the prosthesis to be used is greater than two sizes larger than the native aortic root, even in the absence of tunnel subaortic stenosis. Aside from these circumstances, it is not uncommon for the small root to be present in an isolated context. A typical example, illustrated in this article, is an adolescent boy with congenital aortic stenosis who has undergone a few attempts at balloon valuvuloplasty as a neonate and infant, who continues with persistent gradient at the valvar level. Often, there is accompanying aortic insufficiency. Indeed, aortic insufficiency would be more pronounced in these children than those with subvalvar obstruction because of limitation of backward flow by the subvalvar element.
Other indications for the use of a posterior root enlarging procedures include the need for replacement of the mitral valve simultaneous with the aortic valve
Furthermore, in an infant with combined mitral and aortic stenosis, enlargement of the mitral and aortic annuli could be accomplished simultaneously.
If simultaneous aortic and mitral replacement is performed, careful inspection of the left ventricular outflow tract is mandated. The ring of a large mitral prosthesis may protrude into this space, defeating the original goal of the operation.
Furthermore, the placement of a rigid mitral prosthesis can reduce the effective available space for the placement of the aortic prosthesis. Therefore, the aortic annulus should be resized after placement of the mitral valve prosthesis before commencement of aortic valve replacement. Alternatively, the aortic valve prosthesis may be seated before mitral valve replacement, although this could make the placement of the sutures through the anterior annulus of the mitral valve somewhat cumbersome. Sankar and coworkers have reported that in patients undergoing double valve replacement, enlargement of the aortic-mitral curtain by more than 30 mm leads to protrusion of the mitral prosthesis under the aortic prosthesis.
Surprisingly, the mitral regurgitation is not simply associated with the extent of the incision, but rather with the use of synthetic patch material, since the pathology has not been reported in patients in whom autologous pericardium has been used. With this particular problem on echocardiography the basal portion of the AML appears highly echogenic and with poor mobility. Therefore, the marginal portion of the anterior leaflet appears to have relative prolapse compared with the basal portion, with a “hinge” joint in the midportion of the AML. The resultant regurgitant flow is directed toward the posterior wall of the left atrium.
Other reported complications include left atrial to aorta fistula,
and prosthetic valve related complications such as perivalvular leakage and endocarditis. If the AML is incised to any degree more than just minimal, then it is prudent to re-enforce the attachment of the patch to the leaflet tissue and to ensure absence of any tension on those suture lines as demonstrated by the reported complication of acute mitral regurgitation postoperatively because of separation of the patch material from the AML.
Most studies have demonstrated the superiority of the annular enlarging procedures to placement of small valve prostheses. Unfortunately however, none of these studies have focused on the pediatric population solely and are rather a compilation of both adults and children. Nevrtheless, the posterior annular enlarging procedure emains a useful adjunct to the armamentarium of the longenital heart surgeon.