Transposition of the great arteries with straddling tricuspid valve. Report of two rare cases with acquired subaortic stenosis after main pulmonary artery banding.

The clinical, hemodynamic, angiocardiographic, and postmortem findings of a previously unreported type of subaortic stenosis are presented in two patients who also had straddling tricuspid valve and transposition of the great arteries. The subaortic stenosis became apparent after banding of the main pulmonary artery and was due to hypertrophy of a probably abnormally positioned moderator band resulting in a double-chambered right ventricle. Fibrous tissue accumulation at the stenotic os infundibuli also contributed to the subaortic obstruction. Both patients had situs solitus of the atria. Patient 1 had ventricular inversion (L-loop ventricles) and atresia of the right-sided mitral valve. Patient 2 had normally positioned ventricles (D-loop) and two atrioventricular valves. The presence of a large left ventricle and a small right ventricle in the angiocardiogram led to the erroneous diagnosis of a single left ventricle with an infundibular outlet chamber in both patients. Consequently, the subaortic obstruction was thought preoperatively to be at the site of a restrictive bulboventricular foramen. Patient 1 died 36 hours after placement of a valved conduit from the left ventricle to the descending aorta. Patient 2 was operated on successfully and the surgical procedures performed are described.