Transposition of the Great Arteries

Sequential cardiac catheterizations were performed on 19 infants with complete transposition of the great arteries (TGA). None had any additional cardiac abnormalities other than an atrial septal defect. All were under 3 months of age at the time of the initial study. The pulmonary artery pressures and pulmonary-to-systemic vascular resistance ratios were significantly higher under the age of 9 weeks than over this age. The major fall in pulmonary vascular resistance appeared to occur in the first 4 weeks of life. A systolic pressure gradient from the left ventricle to the pulmonary artery of more than 5 mm Hg (median 13) was found at all the investigations performed in patients over the age of 2 weeks. This suggests that such a pressure gradient is usual in TGA, and not a sign of pulmonary stenosis. No systematic distribution of pulmonary-to-systemic flow ratios or age-related changes in these ratios was demonstrated, but pulmonary flow was rarely the same as systemic flow. In TGA the pulmonary vasculature undergoes a maturation process with the transition from intra- to extrauterine life. This process is similar in magnitude and time scale to that seen in the normal human infant.