**2.1 Ebstein's anomaly is an anomaly with both myocardial and valvular defects**

The chief distinguishing feature of an Ebstein's malformation is the positioning of the hinge point of the tricuspid valve into the right ventricular cavity with an apical and anterior rotated appearance toward the right ventricular outflow tract rather than at its normal location at the atrioventricular junction or annulus, and this is due to failure of the septal and inferior leaflets to delaminate from the underlying myocardium. In addition, Ebstein's malformation is often accompanied by valvar dysplasia, anomalies of the tension apparatus, and myocardial anomalies, and in severe cases, the dilated thin-walled, atrialized inlet component is divided from the apical tubercular and outlet components by a muscular shelf. Furthermore, an Ebstein's anomaly may be associated with an atrial septal defect, pulmonary atresia, or congenitally corrected transposition of the great arteries (ccTGA) and less commonly with pulmonary stenosis, a ventricular septal defect, or an atrioventricular septal defect [1, 8].

A normal morphologic right ventricle (**Figure 1a** and **b**) is divided into inlet, apical trabecular, and outlet components and has a tricuspid valve with its orifice pointing toward the ventricular apex. The tricuspid valve consists of three leaflets designated anterior-superior, inferior, and septal, and its hinge point is located at the annulus. In addition, the tension apparatus of the septal leaflet is attached to the coarsely

#### **Figure 1.**

*Morphology of the right side of a normal heart. (a) Septal surfaces of the right atrium, inlet, and apical components of the ventricle and tricuspid valve. (b) Right ventricular outlet and pulmonary valve and pulmonary trunk.*

## *Ebstein's Anomaly DOI: http://dx.doi.org/10.5772/intechopen.104670*

trabeculated septal surface, and the pulmonary valve is supported by a complete muscular sleeve separating it from the tricuspid valve.

With an Ebstein's anomaly, the extent of the area of failed delamination, and the appearance of atrioventricular valve rotation may vary from mild to severe, and the functional orifice of the tricuspid valve opens toward the ventricular outflow tract. In addition, there is variability in the condition of the tricuspid valve leaflets. The delaminated anterior-superior leaflet may be small or severely deformed with fenestrations, and its tendinous cords can be short and thickened, and in other cases, the leaflet tissue may be redundant and located within the right ventricular outflow tract possibly resulting in an element of obstruction. Moreover, the inferior and septal leaflet tissue can be hypoplastic and dysplastic. However, in some cases, the inferior leaflet may be large and curtain-like with fenestrations, some of which may have a fan-like appearance. **Figure 2** shows the un-delaminated areas of the septal and inferior leaflets. The functional orifice of the tricuspid valve shows the appearance of slight rotation away from the apical component and toward the outlet component. Both the septal and inferior leaflets are dysplastic at the level of their hinge points. The anterior-superior leaflet is dysplastic with thickened tendonous cords. The right ventricular inlet component shows slight atrialization.

**Figure 3a** shows the severe form of Ebstein's anomaly with the hinge point located well within the right ventricular chamber and located on a muscular shelf that separates the inlet and apical trabecular components. Proximal to this muscular shelf, the heart shows marked atrialization and dilatation and the septal surface is smooth with loss of trabeculations. The atrialization in hearts with Ebstein's anomaly can vary from almost non-existent to severe. In severe cases, the atrialized right ventricle can be greatly dilated and affect the shape and function of the left ventricle (**Figure 3b**) [8–10].

#### **Figure 2.**

*Right side of a heart with a moderate Ebstein's anomaly showing the septal and inferior leaflets of the tricuspid valve failure to delaminate from the ventricular wall and a rotational appearing displacement of their hinge points, slight atrialization of the inlet to the right ventricle and a small atrial septal defect at the site of the oval fossa.*

#### **Figure 3.**

*Heart specimens with severe Ebstein's anomaly. (a) Right side showing severe dilatation and marked atrialization of the inlet of the right ventricle with failed delamination of the septal leaflet showing a smooth septal surface and the muscular shelf. The inferior leaflet is curtain-like with short chords attaching it to the muscular shelf. The functional orifice is bifoliate and faces the pulmonary outlet. The dash line shows the solitary zone of apposition, and the arrow heads show the second outlet from the right ventricle. (b) Shows the left ventricle with the septum bulging into the left ventricular cavity because of a severe Ebstein's anomaly of the right side of the heart.*

#### **Figure 4.**

*The outlet components of two hearts with severe Ebstein's anomaly. (a) Shows the bifoliate functional orifice of the tricuspid valve along with multiple tendinous cords attached to the ventricular wall at the junction between the atralized inlet and the functional parts of the right ventricle, the apical trabecular and outlet components. (b) A view of the outlet component from the arterial side showing the functional bifoliate orifice, the only outlet from the inlet and apical components of the right ventricle, directed toward the pulmonary valve. The dash line shows the solitary zone of apposition.*

This heart illustrated in **Figure 3a** shows two exits from the right ventricle. One outlet from the inlet component is through a functional orifice that faces the pulmonary outlet, and this orifice is a bifoliate opening that functionally closes along a solitary zone of apposition. This bifoliate orifice is created by a tongue of valvar tissue joining the anterior-superior to the inferior leaflets. A second exit from the right ventricle is through the proximal outlet component and between tendinous cords.

In some cases of Ebstein's anomaly, the functional bifoliate outlet orifice leaflet can show multiple tendinous cord attachments to the ventricular wall at the junction between the atralized inlet and the apical trabecular and outlet components (**Figure 4a**), or the bifoliate functional orifice may be the only outlet from the right ventricle (**Figure 4b**).

Besides atrial septal defects, Ebstein's malformations have an association with pulmonary atresia. **Figure 5a** shows the right side of a heart with Ebstein's anomaly, which is markedly dilated, shows severe atrialization of the inlet and a very dysplastic atrioventricular valvar leaflet tissue. **Figure 5b** shows the outlet from this right ventricle illustrating the pulmonary atresia and redundant dysplastic atrioventricular valve leaflet tissue.
