Further observations on the spontaneous closure of physiologically advantageous ventricular septal defects in tricuspid atresia: surgical implications.

Clinical, angiographic, and pathological findings in 40 consecutive patients with tricuspid atresia were reviewed. In 14 patients, there was evidence of closure of the ventricular septal defect (VSD); it was complete in 8 and partial in the other 6. Eleven of these VSD closures occurred in type I patients (without transposition of the great arteries) and 3 in type II patients (with transposition). Progressive cyanosis, along with increasing polycythemia or the disappearance of a previously heard murmur, or both, was observed in all patients. The incidence of closure of VSD in this lesion was 42%. Progressive muscular "encroachment" of the margins of the VSD with subsequent fibrosis and covering by endocardial proliferation is thought to be the most likely mechanism of closure. For initial palliation of this defect, a Blalock-Taussig shunt--preferably on the left side--is recommended in preference to a Glenn anastomosis, because the latter may leave the left pulmonary circuit without blood supply if the VSD closes. If further palliation is required prior to a Fontan procedure, a Blalock-Taussig shunt on the right side, Glenn anastomosis, or enlargement of the VSD may be performed. In type II patients, a large and nonrestrictive VSD is essential for survival following a Fontan operation. Therefore, the size of the VSD should be evaluated prior to and at the time of surgical correction. If the VSD is small in type II patients, complete bypass of the defect and right ventricle by a pulmonary artery-ascending aorta shunt or by a left ventricle-descending aorta conduit should be performed.