Morphogenetic considerations on congenital malformations of the outflow tract. Part 2: Complete transposition of the great arteries and double outlet right ventricle.

On the basis of our recent embryologic work concerning the separation process of the outflow tract, our study of the morphology of specimens from the Leiden Collection of malformed hearts, and in conjunction with our review of the literature, we have reconsidered the morphogenesis of complete transposition and double outlet right ventricle. In complete transposition, a mirror-image arrangement of the columns of the aorto-pulmonary septum could explain the discordant ventriculo-arterial connexion and might thus play a role in its development. Dedicating a cardinal role to the aorto-pulmonary septum in the morphogenesis of complete transposition does not, however, seem justified. Double outlet right ventricle is not an embryologic entity. From the stance of the embryologist, we prefer to consider double outlet right ventricle in terms of a feature that may occur in specimens related to hearts with either a concordant ventriculo-arterial connexion (such as tetralogy of Fallot, or the so-called Eisenmenger ventricular septal defect), or a discordant ventriculo-arterial connexion (complete transposition).