Development of the outflow tract

The definitive cardiac outflow tracts have three components: the intra-pericardial arterial trunks, the arterial roots, and the ventricular outflow tracts. Improved correlations between normal development and cardiac malformations can be obtained by analysing the developing outflow tract in tripartite fashion with proximal, intermediate, and distal components. When first seen, the walls of the entire outflow tract express myocardial markers. With ongoing development, the distal border regresses away from the edges of the pericardial cavity. Subsequently, the distal outflow tract becomes the intra-pericardial arterial trunks, with a protrusion from the dorsal wall of the aortic sac forming the aortopulmonary septum. The arterial valves form in the intermediate part of the outflow tract. The proximal part eventually becomes transformed into the ventricular outflow tracts, with muscularization of the proximal cushions producing the right ventricular infundibulum. This approach provides rational explanations for the congenital lesions involving the different parts of the outflow tracts.