transposition of the great vessels, a congenital cardiac anomaly in which the pulmonary artery arises from the left ventricle and the aorta from the right ventricle and there is no communication between the systemic and pulmonary circulations. Life is impossible with this anomaly unless there are associated cardiac defects, such as a septal defect or a patent ductus arteriosus, that enable the mixing of oxygenated and unoxygenated blood. The severity of the condition depends on the type and size of the associated defect. The primary symptoms are cyanosis and hypoxia, especially in infants with small septal defects, although cardiomegaly is usually evident a few weeks after birth. Signs of congestive heart failure develop rapidly, especially in infants with large ventricular septal defects. Definitive diagnosis is based on cardiac catheterization. Surgical correction of the defect is postponed, if possible, until after 6 months of age, when the infant can better tolerate the procedure. Immediate palliative surgical procedures such as the Rashkind procedure may be performed to decrease pulmonary vascular resistance and prevent congestive heart failure. See also blue baby.
