Ebstein anomaly is a defect of the right ventricle that results in variable degrees of failure of delamination of the valve leaflets, leading to tricuspid valve regurgitation and right ventricular dysfunction. The classic pathology is apical (downward) displacement of the tricuspid valve leaflets (most frequently septal followed by posterior and anterior leaflets) with abnormal adherence of the leaflets to the underlying myocardium.

The major morphologic features are apical displacement of the septal leaflet ≥8 mm/m², dilatation of the “atrialized” portion of the right ventricle with variable degrees of thinning of the free wall of the right ventricle [1]. Dilatation of the right atrioventricular junction (true tricuspid annulus) is also seen [1]. See Fig. 12.1. Incompetence of the deformed tricuspid valve and the functional impairment of the right ventricle result in an impediment to forward flow of blood through the right side of the heart. Typically, there are other anatomic abnormalities including a large, redundant anterior leaflet with fenestration and varying degrees of tethering to the right ventricular wall. In most cases there is a patent foramen ovale or secundum atrial septal defect, resulting in a right-to-left shunt due to elevated right-sided pressures.

According to Carpentier’s classification, Ebstein anomaly can be categorized as follows: type A: adequate RV volume; type B: large atrialized segment of the RV and mobile anterior leaflet; type C: restricted movement of anterior leaflet which may cause infundibular obstruction; type D: near-complete atrialization of the RV (Uhl’s syndrome) [2].

Tricuspid atresia is the third most common form of cyanotic congenital heart disease, with a prevalence of 0.3–3.7 % [7]. Tricuspid atresia is characterized by the absence of a tricuspid valve. There is no direct connection between the right atrium and right ventricle, resulting in a small or absent right ventricle that cannot adequately pump blood to the lungs (Fig. 12.4). Depending on the relationship with the great vessels, there are three types of tricuspid atresia. In type I, the great arteries are related normally. With type II, the great arteries are d-transposed, and in type III, the great arteries are l-transposed. These types are further subclassified according to the presence or absence of ventricular septal defects and pulmonary valve pathology [8, 9].

Associated defects coexist in 15–20 % of patients, most frequently transposition of the great vessels and persistent left-sided superior vena cava [7]. Atrial septal defect is ­obligatory in those patients. Extracardiac associations may include a right-sided aortic arch and an absent spleen.

In patients with tricuspid atresia, venous blood returning to the right atrium can exit only through an interatrial communication. Because of the obligatory right-to-left shunt at the level of the atria, saturation of the left atrial blood is diminished. Additionally, intracardiac blood flow depends on coexisting pulmonary artery pathology. With coexistent pulmonary artery or pulmonary valve stenosis, pulmonary blood flow is reduced, resulting in worsening cyanosis. Pulmonary obstruction occurs most often in patients with tricuspid atresia and normal great artery anatomy. In the absence of pulmonary atresia or pulmonary stenosis, the volume of blood flowing to the lungs may be normal thus resulting in decreased cyanosis. Patients with d-transposed great arteries and tricuspid atresia typically have unobstructed pulmonary blood flow.

Tricuspid atresia patients ultimately develop left ventricular systolic dysfunction due to left ventricular volume overload related to the fact that venous blood must return to the left ventricle as well as to the presence of chronic hypoxemia. Left ventricular dysfunction may then lead to mitral annulus dilatation and mitral regurgitation, which further increases left ventricular volume overload.