Asymmetric distribution of the pulmonary blood flow between the right and left lungs in d-transposition of the great arteries.

Pulmonary angiograms, radionuclide lung images and chest roentgenograms were evaluated regarding the incidence, magnitude and natural evolution of maldistribution of the pulmonary blood flow between the lungs in 63 patients with dextrotransposition of the great arteries. Approximately half of these patients had some degree of greater perfusion of the right relative to the left lung. A significant correlation was demonstrated between the incidence of this maldistribution of blood flow and the angulation between the main and the right pulmonary arteries. For any given angulation between these vessels, additional pulmonary stenosis increased the incidence of disparity in perfusion. Our observations suggest the following developmental mechanisms: The maldistribution in flow results from the abnormal rightward inclination of the main pulmonary artery in the transposition malformation which straightens the flow axis from the main to the right pulmonary artery. Under these circumstances the momentum of the blood in the main pulmonary artery carries the blood preferentially into the right pulmonary artery. This momentum is increased when there is stenosis of the left ventricular outflow tract. Consequent differences in the mechanical properties of the two pulmonary vascular beds can increase this maldistribution. The disparity in perfusion between the lungs is not present in newborns with d-transposition, appears to be progressive in severity and in time may result in almost complete cessation of effective perfusion of the left lung. The effect of the Mustard operation on this abnormality of flow is discussed.