Ebstein Anomaly — #1 Embryologic Anatomy

Core concept. Ebstein anomaly is fundamentally a delamination defect of the tricuspid valve. During normal valvulogenesis, the septal and inferior (posterior) leaflets separate (“undermine”) from the right-ventricular (RV) myocardium to become mobile structures suspended by chordae and papillary muscles. In Ebstein anomaly, this delamination is incomplete, leaving leaflet tissue plastered to the RV wall and the hinge line displaced apically into the ventricle while the anatomic annulus at the atrioventricular junction remains near normal [1, 2].

Resulting chamber geometry. Apical displacement of the septal and inferior leaflets partitions the RV into two components:

• an atrialized RV (proximal to the displaced hinge), typically thin-walled, dyskinetic, and contracting in phase with the right atrium; and

• a small functional RV (distal infundibulo-apical portion) that supports forward pulmonary flow. The degree of atrialization and the volume of the functional RV vary widely across the spectrum of disease [1].

Leaflet and subvalvar morphology. The anterior leaflet is often enlarged and “sail-like,” but its excursion is limited by abnormal, shortened, or fenestrated chordae and by malpositioned papillary muscles, leading to malcoaptation. The septal and inferior leaflets remain variably adherent to the RV wall, with basal muscularization and loss of normal chordal architecture; papillary muscles may be dysplastic, fused to the free wall, or maloriented, compounding coaptation failure [1, 2].

Functional consequences and associated lesions. Severe tricuspid regurgitation (TR) is common and drives progressive right-atrial (RA) enlargement; the atrialized segment amplifies apparent RA size. An interatrial communication—patent foramen ovale or secundum ASD—occurs in the great majority of patients and often governs systemic oxygenation by allowing right-to-left shunting when RA pressure is elevated [1]. Accessory atrioventricular pathways and WPW-mediated tachyarrhythmias are frequent due to remodeling at the malformed right AV junction [1]. In advanced forms with a diminutive functional RV, pulmonary valve incompetence and outflow distortion may coexist, further impairing forward output.

Developmental timing and spectrum. Tricuspid leaflet delamination normally completes in late embryonic–early fetal life. The extent and distribution of delamination failure define the clinical continuum—from mild apical displacement with near-normal RV size to severe forms with extensive atrialization and a tiny functional RV. Surgical and imaging parlance often invoke Carpentier types A–D, which correlate with the proportion of atrialized ventricle and the mobility of the anterior leaflet [1].

Surgical relevance (principles that derive from embryology). Because the annulus is anatomically near normal while leaflet hinge lines are displaced apically, modern repair targets three goals:

1. Mobilize and complete delamination of adherent leaflet tissue to recreate circumferential leaflet mobility;
2. Reconstruct a coaptation plane at the true annulus—most reliably accomplished with cone reconstruction that fashions a 360° leaflet cone sutured to the anatomic annulus [3, 4];
3. Restore RV geometry and competence, frequently by excluding or plicating the atrialized segment and performing selective annuloplasty. Contemporary series show durable TR reduction, RV reverse remodeling, and low reintervention rates after cone repair when performed in experienced centers [5]. In adults, indications center on symptoms, progressive RV enlargement/dysfunction, and arrhythmia burden; cone repair is generally the preferred approach, with valve replacement or adjunctive cavopulmonary shunt reserved for advanced disease or inadequate leaflet tissue [6].

References

[1] Paranon S, Acar P. Ebstein’s anomaly of the tricuspid valve: from fetus to adult. Heart. 2008;94(2):237-243.

[2] Zuberbuhler JR, Becker AE, Anderson RH, Lenox CC. Ebstein’s malformation and the embryological development of the tricuspid valve. Pediatr Cardiol. 1984;5(4):289-295.

[3] da Silva JP, Baumgratz JF, da Fonseca L, Franchi SM, Lopes LM, Tavares GMP, et al. The cone reconstruction of the tricuspid valve in Ebstein’s anomaly: early and midterm results. J Thorac Cardiovasc Surg. 2007;133(1):215-223. PubMed

[4] Dearani JA, Said SM, O’Leary PW, Pike RB, Connolly HM, Driscoll DJ, et al. Anatomic repair of Ebstein’s malformation: lessons learned with cone reconstruction. Ann Thorac Surg. 2013;95(1):220-226. PubMed

[5] Holst KA, Dearani JA, Said S, Pike RB, Connolly HM, Cannon BC, et al. Improving results of surgery for Ebstein anomaly: Where are we after 235 cone repairs? Ann Thorac Surg. 2018;105(1):160-168. PubMed

[6] Fuchs MM, Connolly HM. Ebstein anomaly in the adult patient. Cardiol Clin. 2020;38(3):353-363. PubMed