SINGLE VENTRICLE AND SUBAORTIC OBSTRUCTION

In patients with a functional single ventricle, subaortic stenosis occ urs most frequently under one of two circumstances: (1) double-inlet l eft ventricle, which connects with a rudimentary right ventricle leadi ng to the aorta with obstruction to ventricular outflow from narrowing of the bulboventricular foramen, the connection between the dominant left ventricle and the rudimentary right ventricle; and (2) tricuspid atresia, ventricular septal defect, and ventriculoarterial discordance with unobstructed pulmonary blood flow with subaortic obstruction fro m a decrease in the size of the ventricular defect. A subaortic pressu re gradient may be present at birth or be acquired, especially after p ulmonary artery banding or repair of aortic atresia or coarctation. Su rgical treatment of subaortic obstruction is mandatory before or at th e time of a modified Fontan operation.