Repeated aortopulmonary shunt thrombosis in a neonatal patient with a low antithrombin level.

A female infant with unbalanced right ventricular dominant atrioventricular septal defect with double-outlet right ventricle and pulmonary stenosis had recurrent aortopulmonary shunt thrombosis. She was found to have low antithrombin levels and was managed with antithrombin replacement in addition to unfractionated heparin. A subsequent aortopulmonary shunt was successfully placed, and patency was maintained. Her antithrombin levels normalized, and she was continued on low-molecular-weight heparin and aspirin until four months of age when a bidirectional superior cavopulmonary anastomosis was done. A prothrombotic evaluation at the time of the acute thrombosis and repeated at four months of age was negative except for the initially low antithrombin level. A repeat antithrombin level (off supplementation) at the time of the cavopulmonary anastomosis was normal making the diagnosis of congenital antithrombin deficiency unlikely. This case highlights the possibility of neonatal antithrombin deficiency as a cause of aortopulmonary shunt thrombosis and successful management with replacement therapy.