Cyanotic Congenital Heart Disease: Lesions Associated with Increased Pulmonary Blood Flow

Transposition of the great vessels, a common cyanotic congenital anomaly, accounts for ≈5% of all congenital heart disease. In this anomaly, the systemic veins return normally to the right atrium and the pulmonary veins return to the left atrium. The connections between the atria and ventricles are also normal (atrioventricular concordance). The aorta arises from the right ventricle and the pulmonary artery from the left ventricle. Desaturated blood returning from the body to the right side of the heart goes inappropriately right out the aorta and back to the body again, whereas oxygenated pulmonary venous blood returning to the left side of the heart is returned directly to the lungs. The systemic and pulmonary circulations consist of two parallel circuits. Survival in these newborns is provided by the foramen ovale and the ductus arteriosus, which permit some mixture of oxygenated and deoxygenated blood. About 50% of patients with TGA also have a ventricular septal defect (VSD), which provides for better mixing. The clinical findings and hemodynamics vary in relation to the presence or absence of associated defects. TGA is more common in infants of diabetic mothers and in males (3 : 1). Before the modern era of corrective or palliative surgery, mortality was >90% in the 1st yr of life.