Embryological observations on the formal pathogenesis of double-outlet left ventricle with a right-ventricular infundibulum.

The term 'double-outlet left ventricle' (DOLV) denotes congenital heart malformations in which the aorta and the pulmonary trunk both arise entirely or predominantly above the morphologically left ventricle. In the past, the formal pathogenesis of DOLV was explained by an abnormal topogenesis of the origin of the great arteries, which could be caused by an excessive leftward shift of the embryonic conotruncus, or by errors in differential conal growth or absorption. However, modern embryological and pathological research is casting doubt on the validity of these concepts. In the present paper we demonstrate a case of DOLV found in a chick fetus. In this heart the main derivatives of the embryonic conotruncus (right-ventricular infundibulum and proximal portions of the great arteries) principally are in the normal position and of normal dimensions. The anomaly leading to DOLV under these conditions is a misalignment of the ventricular septum. The subarterial portion of the ventricular septum above the crista supraventricularis is not oriented in the normal oblique plane between the pulmonary and aortic valve, but is oriented in a frontal plane anterior to the origin of both great arteries. The consequences of this anomaly are the separation of the right-ventricular infundibulum from the origin of both great vessels (DOLV) and a lack of continuity between the malpositioned portion of the ventricular septum (posterior wall of the right-ventricular infundibulum) and a septum dividing the semilunar valve level. The infundibulum of the right ventricle is derived from the upstream portion of the embryonic conotruncus (conus) whereas the semilunar valves and great arteries are derived from its downstream protion (truncus arteriosus) and the aortic sac. Therefore, our findings suggest that the division of the conotruncus is performed by at least two different septa, one dividing the conus and another dividing the truncus arteriosus and aortic sac. The misalignment of the ventricular septum leading to the presented type of DOLV could result from a misalignment of the septal anlagen of the embryonic conus, the conus ridges. Our findings are discussed with respect to human cases of DOLV and with respect to a recent concept on the septation of the embryonic conotruncus.