Michael P. D'Alessandro, M.D.
Peer Review Status: Internally Peer Reviewed
The aorta arises from the right ventricle, and the pulmonary artery arises from the left ventricle.In 85% of the cases the aorta is anterior and to the right of the pulmonary artery (D-TGA). The venous connections with the atria are normal and the right and left atria connect to the morphologic right and left ventricles. Therefore the pulmonary and systemic circulations are in parallel and a communication between the two is needed. Communications can include a VSD (seen in 50%), ASD / foramen ovale, and PDA. Pulmonary stenosis can be present, and 10-15% have a right aortic arch.
TGA is the first consideration in a cyanotic infant with increased vascularity. The increased vascularity is due to the VSD or PDA. There is a flat or concave pulmonary artery segment, a narrowed upper mediastinum, and moderate cardiomegaly. The narrowed mediastinum is due to the anterior aorta with anteroposterior orientation of the arch, posteromedial displacement of the pulmonary artery, and stress related thymic atrophy.There often is preferential blood flow to the right pulmonary artery because the right pulmonary artery lines up with the right ventricle outflow track. The egg shaped heart is due to right atrial and left ventricle dilation. The narrow mediastinum and egg shaped heart cause an "egg on a string" appearance.
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