Variation in the size and distensibility of the pulmonary arteries in d-transposition of the great arteries

Abstract

The relative size of the main pulmonary artery was determined from cineangiograms of 117 patients with d-transposition of the great arteries by calculating the ratio between the diameters of the main pulmonary artery and aorta. The pulmonary artery was largest in patients with ventricular septal defect or patent ductus arteriosus, or both, because of increased pulmonary arterial pressure and flow. In patients with an intact ventricular septum or with left ventricular outflow tract obstruction, or both, the main pulmonary artery was approximately the size of the aorta. Two cases of d-transposition and gross dilatation of the main pulmonary artery and hypoplastic first branch pulmonary arteries are presented. In these cases the ratio between the diameters of the main pulmonary artery and aorta was greater than in any of the other 117 cases studied. Distensibility of the right pulmonary artery in 18 patients with d-transposition was assessed by determining the percent change in radius and the pressure-strain elastic modulus from the cineangiograms. In patients with intact ventricular septum the distensibility was similar to that reported for normal control subjects, but increased pulmonary arterial pressure due to a ventricular septal defect resulted in stiffer vessels. In comparison with these 18 patients the 2 patients with a grossly dilated main pulmonary artery had an excessively distensible main pulmonary arterial wall as indicated by a greater percent change in radius and abnormal tension-strain relation. Excessive distensibility of the main pulmonary artery and hypoplasia of the first branch pulmonary arteries allowed a greater accommodation of left ventricular stroke volume in the main pulmonary artery and hence resulted in their gross dilatation.