At autopsy in 1866, Wilhelm Ebstein described an enlarged and fenestrated anterior leaflet of the tricuspid valve. The posterior and septal leaflets were hypoplastic, thickened and adherent to the right ventricle [6]. Indeed, the leaflets of the tricuspid valve are often thickened and dysplastic in the setting of Ebstein anomaly [7]. Fenestrations, particularly of the anterior leaflet, are often present. In addition, tethering of the anterior leaflet is often seen and is caused by chordal attachments to the ventricular free wall and/or displaced papillary muscles. The anterior leaflet is generally elongated and, if redundant, may obstruct the right ventricular outflow tract [5]. The malformed tricuspid valve leaflets often result in stenosis or regurgitation; however, the latter is far more common. The functional integrity of the tricuspid valve in Ebstein anomaly generally depends on several factors: (a) the degree of displacement of the right atrioventricular junction, (b) the extent of dysplasia and the presence/size of fenestrations, (c) the size and restriction of the anterior leaflet and/or (d) the dimension of the ‘functional’ tricuspid valve annulus. Of note, the degree of displacement of the right atrioventricular junction has important relevance for disease severity and ultimate prognosis in adult patients [8].

In addition to tricuspid valve disease, Ebstein anomaly is characterised by a wide spectrum of right ventricular development. In severe forms, the atrialised portion of the right ventricle can become disproportionally large, a finding which has been shown to be associated with poor prognosis in both children [9] and adults [8, 10]. The apex of the functional right ventricle is often heavily trabeculated although the myocardium itself may be thinned or even aneurysmal. In the extreme form, replacement of the myocardium with fibrous tissue has been observed [11]. Although hypoplasia of the functional right ventricle is often seen in neonates and young children with moderate to severe forms of Ebstein anomaly (as a result of downward displacement of the right atrioventricular junction), in adults, conversely, the indexed volume of the functional portion of the right ventricle is typically normal or may even be dilated [12–14]. In two recent studies, dilatation of the functional right ventricle was associated with the severity of tricuspid regurgitation suggesting a mechanistic link between valve insufficiency and enlargement of the functional right ventricle [14, 15] (Fig. 15.4). Unlike neonates, in these studies of adults, there was a linear relationship between the magnitude of apical displacement and the size of the functional right ventricle, likely reflecting an adaptive response to long-standing volume overload from tricuspid regurgitation.

Numerous lesions can be seen in conjunction with Ebstein anomaly. Interatrial communications, such as a secundum atrial septal defects or a patent foramen ovale, are the most common and are reported in more than 80 % of cases [16] (Fig. 15.5). Other associated findings include patency of the arterial duct, ventricular septal defects, pulmonary stenosis/atresia, bicuspid aortic valve, aortic stenosis/atresia, coarctation of the aorta and/or mitral valve defects (Fig. 15.6).

Congenitally corrected transposition of the great arteries (cc-TGA) is often associated with an Ebstein-like malformation of the tricuspid valve. In this condition, there are discordant atrioventricular and ventriculo-arterial connections. The tricuspid valve is associated with the subaortic ventricle and, therefore, is exposed to higher pressure as compared with typical Ebstein anomaly with concordant atrioventricular connections where the tricuspid valve is associated with the subpulmonic ventricle. The dysplastic tricuspid valve in cc-TGA can occur without or with apical displacement of the septal and posterior leaflets. Unlike classic Ebstein anomaly, in cc-TGA, other typical features tend to be absent (i.e. there is no rotational displacement of the septal and posterior tricuspid leaflets, the anterior leaflet may not be elongated, adherence of the septal and posterior leaflets is limited, the atrialised portion of the right ventricular inflow is generally small, and the inlet portion of the right ventricular myocardium tends not to be dilated or thinned) [17–21].

Of note, left ventricular myocardial abnormalities and left heart lesions are commonly seen in Ebstein disease. In about 20 % of patients with Ebstein anomaly, noncompaction of the left ventricular myocardium has been described [22]. It is important to note that, despite potential links at the time of embryologic development, the extent of noncompaction does not mirror severity of Ebstein anomaly suggesting additional phenotypic modifiers (Fig. 15.7) [22, 23].

The apical displacement of the septal tricuspid valve leaflet may result in discontinuity of the central fibrous body and septal atrioventricular ring, creating a potential substrate for accessory pathway formation. Specifically, Wolff-Parkinson-White syndrome is seen and has been documented in up to 36 % of patients with Ebstein anomaly [24, 25]. In the adult population with further atrial enlargement, patients with Ebstein anomaly are predisposed to other supraventricular arrhythmias such as ectopic atrial tachycardia, atrial flutter or atrial fibrillation [25]. Ventricular arrhythmias (in the setting of myocardial fibrosis or in the context of left ventricular noncompaction) have been described, although are far less common than atrial arrhythmias. [22, 25]

The most common entities to consider in the differential diagnosis for Ebstein anomaly include tricuspid valve dysplasia and Uhl’s anomaly. Tricuspid valve dysplasia is a condition defined as a spectrum of congenital anomalies of the tricuspid valve leaflets, chordae and papillary muscles often resulting in tricuspid regurgitation. Although the tricuspid valve may be dysplastic or redundant in the setting of Ebstein anomaly (Fig. 15.8), in the case of isolated tricuspid valve dysplasia, there is no apical displacement of the septal leaflet, and ventricular dysplasia is absent (in contrast to Ebstein anomaly). Uhl’s anomaly is characterised by complete or partial absence of the myocardial layer of the right ventricle. Unlike Ebstein anomaly, the tricuspid valve is not involved in the disease process. Uhl’s anomaly is rarely associated with other cardiac malformations.

In the most extreme form of Ebstein anomaly, cyanosis and heart failure become apparent within the first days of life. Despite recent advances in surgical and medical treatment in congenital heart disease, symptomatic newborns with Ebstein anomaly continue to have dismal outcomes, even in contemporary series [26–28]. Perhaps as a consequence of high mortality in neonatal life, selection bias dictates that adult survivors of Ebstein anomaly will represent the milder form of the disease spectrum.

In milder forms of Ebstein anomaly, patients may be asymptomatic throughout adult life. Although adults may come to medical attention with signs of heart failure or symptomatic arrhythmia [10], fatigue and exercise intolerance are common presentations (Fig. 15.9). Indeed, peak oxygen uptake is reduced in most patients with Ebstein anomaly; the mean aerobic capacity (peak VO₂) in a meta-analysis of 230 patients (mean age 22.9 years, 51.5 % male) was about 21 ± 7 ml/min/kg, and half of those studied had an aerobic capacity <60 % of predicted for normal [29]. Decreased aerobic activity has been associated with low resting oxygen saturation [30

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