Ebstein's anomaly of the tricuspid valve (TV) is a congenital cardiac malformation of the tricuspid valve (TV) and right ventricle (RV) characterized by downward displacement of the functional annulus usually involving septal and inferior leaflets. Ebstein's anatomical spectrum is highly variable. This anatomical study aimed to unravel the morphogenetic mechanisms underlying this variability.

Forty-two hearts exhibiting Ebstein anomaly from the Reference Center for Complex Congenital Heart Defects (CHD) collection were macroscopically analysed: 28 isolated and 14 associated with another CHD. Tricuspid leaflets, right ventricle (RV), and associated lesions were analysed. Measurements were related to fetal heart reference values according to gestational age. Specimens were classified depending on the distal insertion of the anterior leaflet: linear, hyphenated or focal.

Among isolated Ebstein hearts, distal insertion of the anterior leaflet was linear in 36%, hyphenated in 29% and focal in 36%. Linear insertion was always associated with anterior TV orifice and absent inferior leaflet, with absent septal leaflet in 80%. Atrialisation (thin, paper-like, inferior RV wall) was found in 90% of the linear forms and 37.5% of the hyphenated forms, which were associated with various degrees of inferior and septal leaflets non-delaminationanomalies. In focal forms, only the septal leaflet was involved, and there was no atrialisation. Ventricular septal defect was found in 3 specimens, Uhl-like RV anterior wall in 2, including 1 with left ventricle non compaction. Associated Ebstein anomalies were predominantly found in pulmonary atresia with intact ventricular septum; there was no atrialisation and septal leaflet only was involved.

Ebstein anomaly corresponds to an arrest in TV development, early in linear forms, late in focal forms, intermediate in hyphenated forms. Atrialisation was always associated with absent inferior leaflet, underlining developmental interaction between endocardial cushions and myocardium at the RV inferior wall.