Heparin-induced thrombocytopaenia due to heparin flushes: report of two cases

Autoimmune Heparin-Induced Thrombocytopenia

Autoimmune thrombocytopenia (aHIT) is a severe subtype of heparin-induced thrombocytopenia (HIT) with atypical clinical features caused by highly pathological IgG antibodies ("aHIT antibodies") that activate platelets even in the absence of heparin. The clinical features of aHIT include: the onset or worsening of thrombocytopenia despite stopping heparin ("delayed-onset HIT"), thrombocytopenia persistence despite stopping heparin ("persisting" or "refractory HIT"), or triggered by small amounts of heparin (heparin "flush" HIT), most cases of fondaparinux-induced HIT, and patients with unusually severe HIT (e.g., multi-site or microvascular thrombosis, overt disseminated intravascular coagulation [DIC]). Special treatment approaches are required. For example, unlike classic HIT, heparin cessation does not result in de-escalation of antibody-induced hemostasis activation, and thus high-dose intravenous immunoglobulin (IVIG) may be indicated to interrupt aHIT-induced platelet activation; therapeutic plasma exchange may be required if high-dose IVIG is ineffective. Also, aHIT patients are at risk for treatment failure with (activated partial thromboplastin time [APTT]-adjusted) direct thrombin inhibitor (DTI) therapy (argatroban, bivalirudin), either because of APTT confounding (where aHIT-associated DIC and resulting APTT prolongation lead to systematic underdosing/interruption of DTI therapy) or because DTI inhibits thrombin-induced protein C activation. Most HIT laboratories do not test for aHIT antibodies, contributing to aHIT under-recognition.

Heparin-Induced Thrombocytopenia Associated with a Heparin-Bonded Stent Graft

We describe a case of heparin-induced thrombocytopenia (HIT) in association with heparin-bonded stent grafts. A 61-year-old man with claudication secondary to a left superficial femoral artery (SFA) occlusion was treated with 2 heparin-bonded polytetrafluorethylene (hep-PTFE) grafts. Despite the use of antiplatelet medication, he presented with thrombosed hep-PTFE grafts 1 week after initial treatment. An additional hep-PTFE graft was placed at the SFA origin because of migration of the first graft. He was discharged on anticoagulation; however, he presented again 2 weeks later with recurrent SFA thrombosis and a platelet count of 60,000, raising suspicion for HIT. All exogenous forms of heparin were discontinued, and he was started on an alternative anticoagulant. The patient returned again 5 days after being discharged with recurrent symptoms of acute limb ischemia. He underwent a left femoropopliteal artery bypass with autogenous conduit and removal of the grafts. He has since had an uneventful recovery. We believe HIT should be considered as a potential cause of hep-PTFE graft thrombosis. Diagnosis and management of these patients is complex and may require explantation of the graft.