Restrictive ventricular septal defect and critical subaortic stenosis in tetralogy of Fallot.

Introduction: Tetralogy of Fallot is characterized by a non-restrictive malalignment ventricular septal defect (VSD), an overriding aorta and right ventricular outflow tract obstruction resulting from anterior deviation of the infundibular septum. Due to the large VSD, systolic pressures are equal in both ventricles. In rare cases, redundant tricuspid valve tissue may prolapse into the VSD resulting in restriction of the defect size and causing suprasystemic pressure in the right ventricle. Subaortic obstruction by prolapse of the redundant tricuspid tissue into the left ventricular outflow tract, although theoretically possible in this situation, has not been described yet in the literature.
Case Report: We report on a newborn with tetralogy of Fallot presenting with cyanosis and severe arterial hypotension a few hours after birth. Echocardiography revealed redundant hammock-like accessory tricuspid valve tissue almost completely occluding the originally large VSD. Suprasystemic pressure in the right ventricle resulted in protrusion of tricuspid valve tissue across the VSD and thereby caused severe left ventricular outflow tract obstruction. Emergency pulmonary balloon valvuloplasty performed for decompression of the right ventricle, reduced prolapse of tricuspid tissue into the left ventricular outflow tract and resulted in significant improvement of pulmonary and systemic blood flow.
Conclusion: In tetralogy of Fallot, accessory tricuspid valve tissue may obstruct the VSD as well as the left ventricular outflow tract resulting in a life threatening condition in newborns shortly after birth.