Embryological observations on the morphogenesis of double-outlet right ventricle with subaortic ventricular septal defect and normal arrangement of the great arteries.

Double-outlet ventricle (DORV) is generally regarded as a congenital heart defect resulting from impaired morphogenesis of either the outflow portion (conotruncus) or the conoventricular flange (crista prima) of the embryonic heart. However, we demonstrate in this study chicken fetal hearts with DORV in which the conotruncal derivatives (great arteries and subpulmonary part of the ventricular septum = conus septum) and the region of the crista prima are normally developed. The anomalies leading to DORV under these conditions are found at the atrioventricular region. The posterior-anterior axis of the tricuspid orifice is not directed to the right anterior but to the left anterior side of the heart. Thereby the posterior connection line between the muscular ventricular septum and conus septum, which usually follows the left margin of the tricuspid orifice, is not connected to the right portion of the conus septum but instead is directed towards the left portion of the conus septum. In consequence of the abnormal connection between the muscular ventricular septum and the conus septum, the interventricular foramen is formed at the left side of the subaortic flow path. The subaortic flow path arises from the right ventricle. These findings show that DORV can result not only from impaired development of the conotruncus or conoventricular flange, but also from abnormal development of the atrioventricular region. We suggest distinguishing between conotruncal, conoventricular (crista prima), and atrioventricular types of DORV.