Refractory autoimmune heparin-induced thrombocytopenia following cardiac surgery.

Autoimmune heparin-induced thrombocytopenia (aHIT) is a severe subtype of HIT characterized by persistent thrombocytopenia and prothrombotic condition even though anticoagulation with heparin has been discontinued. Here we report on a patient with a previous history of aHIT where re-exposure to heparin during cardiac surgery resulted in recurrent aHIT with pulmonary embolism. Alternative anticoagulants as well as high dose intravenous immunoglobulin were ineffective, and only multiple cycles of therapeutic plasma exchange (TPE) restored platelet counts and prevented further thrombosis progression. The therapy was guided by an ex vivo model of anti-platelet factor 4 (PF4)-mediated thrombosis that showed accurate performance in predicting the clinical outcome. Most importantly, the ability to induce thrombus formation was mainly caused by anti-PF4 (heparin-independent) antibodies. Our paper provides the first description of recurrent aHIT with translational evidence that pathogenic heparin-independent anti-PF4 Abs can be specifically targeted by TPE, emphasizing the clinical use in refractory cases of aHIT.