The atrioventricular junctions in Ebstein malformation

Objective-To review the anatomical structure of the right atrioventricular junction, including the specialised atrioventricular conduction system in hearts with Ebstein's malformation, to identify potential substrates for the abnormalities in conduction. Methods-Five heart specimens representing the morphological spectrum of Ebstein malformation were examined grossly and histologically. Results-On the endocardial surface, the atrioventricular junction was marked by a faint line in two hearts, and by a small ridge in the other three. Analysis of the right parietal junction in four hearts revealed only two accessory muscular atrioventricular connections. A plane of fibrofatty tissue separated atrial from ventricular myocardium in the right parietal junction in all hearts. The compact atrioventricular node was closer to the coronary sinus than usual. Accessory nodoventricular connections were present in four hearts, while accessory fasciculo-ventricular connections were found in one. The right bundle branch was hypoplastic or absent in four hearts. Conclusions-In this small series, the parietal atrioventricular junction was better developed than previously thought. Structural abnormalities of the atrioventricular conduction system, however, were present. These may account for some of the conduction abnormalities frequently observed with the Ebstein malformation.