Transposition of the great arteries (TGA) essentially means ventricular arterial discordance. These lesions represent 5% to 7% of all CHD and have a high mortality within the first year of life.16 Complete transposition describes a patient with appropriate atrioventricular concordance but ventriculo-arterial discordance. As such, the right atrium is connected to the right ventricle via the tricuspid valve but the right ventricle is connected to the systemic artery, the aorta (Figure 12–11). The left atrium is likewise connected via the mitral valve to the left ventricle, which in turn is connected incorrectly to the pulmonary artery. The coronary arteries emerge from the aorta. Consequently, without other defects in the heart, deoxygenated blood would only be delivered to systemic circulation as blood flow is in parallel and not in series. However, this condition is associated with other defects including a patent ductus arteriosus (PDA), patent foramen ovale (PFO), and VSD (Figure 12–12). Consequently, oxygenated and deoxygenated blood intermix permitting transient survival until surgical repair can be undertaken. Without mixing of blood secondary to other structural defects life would not be possible. In patients with TGA and a VSD mixing occurs in the ventricle. In those patients born with an intact interventricular septum blood mixing is dependent upon a PFO, ASD, or PDA. Prostaglandin E1
infusions are at times needed to preserve PDA blood flow. Likewise, balloon atrial septostomy in the catheterization laboratory can be performed to increase the connection between the systemic and pulmonary circulations at the atrial level (Figure 12–13). Other patients may be given a BT shunt to improve pulmonary blood flow (Figure 12–14).