02 February 2007
Background: Distal right-sided outflow obstruction remains a problem after arterial switch operation. We studied the anatomical features of the pulmonary trunk (PT) and its branches that are susceptible to right and left pulmonary arterial (RPA and LPA) hypoplasia in transposition of the great arteries (TGA). Methods: One hundred and one angiograms of TGA performed between 1981 and 1996 were viewed, and Polaroid photos were taken at end-systole. The diameters of RPA, LPA, PT, duct, ascending aorta, and angles between PA and PT were measured, and the ductal flow direction was recorded. Results: Forty-eight cases (47.5%) had a PA/PT diameter ratio (both PAs had same size) below 0.49. A smaller PA/PT was significantly related to posterior inclination of the proximal PT [narrower right (r = 0.50, p < 0.00001) and left (r = 0.48, p < 0.00001) PA-PT angle in lateral view] and a larger duct (r = 0.37, p < 0.0001). Eighteen patients had a follow-up angiogram after a mean period of 8.5 months. Those with a closed duct had evident PA growth (n = 12, 0.51 ± 0.09 to 0.74 ± 0.17, p < 0.0001), but four patients with an attenuated duct had no significant change (0.58 ± 0.06 to 0.68 ± 0.08, p = NS), and one with a persistent large duct had even regression of PA/PT (0.36–0.19). The direction of ductal flow was toward the aorta during early systole on cineangiogram. Conclusions: First-branch PA hypoplasia, which is frequently seen in TGA, was related to the right-to-left shunt through a duct resulting in hemodynamic starvation, and to posterior inclination of the proximal PT in this setting. Natural regression of the duct facilitated PA growth.