Tricuspid Valve Repair for Ebstein's Anomaly

Abstract

E bstein's anomaly is a malformation of the tricuspid valve and right ventricle that is characterized by a spectrum of several features which include: 1) adherence of the tricuspid leaflets to the underlying myocardium (failure of delamination); 2) downward (apical) displacement of the functional annulus (septal > posterior > anterior); 3) dilation of the portion of the right ventricle with variable degrees of hypertrophy and thinning of the wall; 4) redundancy, fenestrations, and tethering of the anterior leaflet; and 5) dilation of the right atrioventricular junction (true tricuspid annulus). 1 With increasing degrees of anatomic severity of malformation, the fibrous transformation of leaflets from their muscular precursors remains incomplete, with the septal leaflet being the most severely involved and the anterior leaflet being the least severely involved. This results in a downward displacement of the hinge point of the posterior and septal leaflets in a spiral fashion below the true annulus. The tricuspid leaflets are usually bizarre and dysplastic, and are tethered by short chordae and papillary muscles or attached to the underlying myocardium directly by muscular bands. Chordae may be few to absent, and leaflet fenestrations are common. The spectrum of severity is variable, and no two hearts with the malformation are exactly alike. In the most severe cases, the septal leaflet is only a ridge of fibrous tissue that originates below the membranous septum and is directed toward the apex. There are varying degrees of delamination of all three leaflets. While the anterior leaflet is the most likely to have some degree of delamination, it may also be severely deformed so that the only mobile leaflet tissue is displaced into the right ventricular outflow tract. The malformed tricuspid valve is usually incompetent, but it may occasionally be stenotic or, rarely, imperforate. In less severe cases, the anterior leaflet may form a large sail-like intracavitary curtain; this structure forms the basis of tricuspid valve repairs. A littlementioned characteristic of the anterior leaflet that is critical to most tricuspid valve repairs is the presence of a free leading edge. The leading edge of the anterior leaflet can be free and mobile (no attachments to underlying endocardium), have hyphenated attachments (focal, segmental direct attachments to the underlying endocardium), or linear direct attachment (entire leading edge is attached to the endocardium). 2 In each case, there can be partial or complete delamination of the remaining portion of the leaflet. In the absence of a free leading edge, suboptimal repairs have been achieved. The atrialized ventricle is characteristically thinned and dilated, but careful observation shows that the entire wall of the right ventricle, both proximal and distal to the abnormal insertion of the tricuspid leaflets, including the infundibulum, is also dilated. Dilation of the right ventricular wall is associated not only with thinning of the wall, but also with an absolute decrease in the number of myocardial fibers. 3 The atrioventricular node is located at the apex of the triangle of Koch, and the conduction system is in its normal position. Atrial septal defect and other associated anomalies are common. A biventricular repair is usually possible. Adjunctive use of atrial fenestration or a bidirectional cavopulmomary shunt is controversial; neither is used routinely in our practice. We occasionally use bidirectional cavopulmonary shunt selectively when the right ventricle is severely dilated and functioning poorly. Since concomitant left ventricular dysfunction may be present when the right ventricle fails, it is important to document by direct pressure measurements that the pulmonary arterial and left atrial pressures are low; otherwise, the bidirectional cavopulmonary shunt will not be feasible. In some circumstances when significant left ventricular dysfunction has occurred, cardiac transplantation may be the best option.