Morphological aspects of Ebstein's anomaly in adults

The essence of the Ebstein's malformation is that the tricuspid valve leafl ets do not attach normally to the valve annulus, and the effective orifice is displaced downward into the right ventricular cavity at the junction of the inlet and trabecular components of the right ventricle. Only the septal and posterior leaflets are displaced and divide the right ventricle into t wo portions. The inlet portion is usually integrated functionally with the right atrium ("atrialized portion"), while the other,, including the trabec ular and outlet portions, constitutes the functional right ventricle. The p roximal atrialized right ventricle often has a wall thinner than the distal functional right ventricle, due to partial congenital absence of myocardiu m. An atrial septal defect is present in more than one-third of hearts, and the majority of the remainder has a patent foramen ovale resulting in a ri ght-to-left shunt. The downward displacement of the septal tricuspid valve leaflet is associated with discontinuity of the central fibrous body and se ptal atrioventricular ring, thus creating a potential substrate for accesso ry atrioventricular connections and ventricular pre-excitation malting the patient at risk of sudden death. Angiography has demonstrated that a signif icant number of patients with Ebstein's anomaly also have morphofunctional abnormalities of the left ventricle, which may be explained by increased fi brosis in the left ventricular wall and ventricular septum as demonstrated by histological studies. Regarding embryology, the leaflets and tensile app aratus of the tricuspid valve are believed to be formed mostly by a process of delamination of the inner layers of the inlet zone of the right ventric le. The downward displacement of the leaflets in Ebstein's anomaly suggests that delamination from the inlet portion failed to occur.