Antithrombin III Deficiency in Patients Requiring Mechanical Circulatory Support

Introduction: Antithrombin or antithrombin III is a vitamin K-independent, natural anticoagulant that is the major inhibitor of thrombin. With the binding of heparin, a conformational change in antithrombin occurs that increases the inactivation of thrombin by antithrombin by 4000-fold. Antithrombin deficiency can be hereditary or acquired; the acquired form is frequently encountered in patients requiring mechanical circulatory support. Cases: A retrospective chart review was performed of patients requiring mechanical circulatory support, 2 patients were identified as being antithrombin deficiency and received antithrombin replacement therapy. Patient 1 required extracorporeal membrane oxygenation (ECMO) for cardiogenic shock secondary to myocardial infarction. The ECMO oxygenator repeatedly clotted, which triggered an investigation into the failure of anticoagulation. The clots dissolved after replacement of the antithrombin III. Patient 2 required biventricular assist device placement for cardiogenic shock secondary to myocardial infarction. On day 5 both the right and left ventricle devices developed clot and the hematologic work-up diagnosed antithrombin III deficiency. After replacement of the antithrombin III the clot in the device chamber resolved. Conclusions: Routine monitoring of antithrombin levels in patients requiring mechanical circulatory support is advisable and cost efficient. Institutions that routinely care for patients requiring mechanical circulatory support should have protocols for triggering the monitoring of antithrombin levels as well as triggers for therapeutic intervention when patients are found to be antithrombin deficient.