Anticoagulation of patients with heparin-induced thrombocytopenia in cardiac surgery

Cardiac transplantation and/or mechanical circulatory support device placement using heparin anti-coagulation in the presence of acute heparin-induced thrombocytopenia

BACKGROUND

Patients with congestive heart failure, decreased left ventricular function, and debilitation are frequently maintained on anti-coagulants, including heparin. As such, these patients are at high risk for developing heparin-induced thrombocytopenia (HIT). Some of these HIT-positive individuals will ultimately undergo urgent heart transplantation or placement of a mechanical circulatory support device (MCSD). Such procedures require cardiopulmonary bypass (CPB) and full anti-coagulation. The safety of re-exposure to heparin during CPB despite the presence of recent-onset thrombocytopenia and Hep/PF4 antibodies has not been studied in the transplant or MCSD populations.

METHODS

Over a 24-month period, 75 heart transplants and 55 MCSD implants were performed. Fourteen patients with acute HIT (thrombocytopenia and positive Hep/PF4 antibody by enzyme-linked immunosorbent assay [ELISA]) and 3 patients with a history of remote HIT underwent cardiac transplantation (n = 9) and/or MCSD placement (n = 8) using heparin as the anti-coagulant during CPB. The median time from diagnosis to CPB was 4.5 days in patients with acute HIT.

RESULTS

Thirty-day survival was 100% in transplant patients and 75% in MCSD patients. Post-transplant ELISA testing was found to be negative in 4 patients with acute HIT and 3 with remote HIT.

CONCLUSIONS

This series demonstrates that short-term re-exposure to heparin during urgent CPB for heart transplantation or MCSD placement is safe despite the presence of thrombocytopenia and Hep/PF4 antibodies. Moreover, the rapid clearance of Hep/PF4 antibodies in our transplant patients suggests a potential therapeutic role for immunosuppressive therapy in the management of HIT in the acute setting.

Management of anticoagulation in patients with subacute heparin-induced thrombocytopenia scheduled for heart transplantation

Anticoagulation management of patients with recent heparin-induced thrombocytopenia (HIT) requiring cardiopulmonary bypass (CPB) surgery is a serious challenge, and especially difficult in patients requiring urgent heart transplantation. As nonheparin anticoagulants during CPB bear a high risk of major bleeding, these patients are at risk of being taken off the transplant list. Short-term use of unfractionated heparin (UFH) for CPB, with restriction of UFH to the surgery itself, is safe and effective in patients with a history of HIT who test negative for antiplatelet factor 4 (PF4)/heparin antibodies. We present evidence that it is safe to expand the concept of UFH reexposure to patients with subacute HIT (ie, those patients with recent HIT in whom the platelet count has recovered but in whom anti-PF4/heparin IgG antibodies remain detectable) requiring heart transplantation, if they test negative by a sensitive functional assay using washed platelets. This can be lifesaving in patients with end-stage heart failure.

Direct thrombin inhibitors: pharmacology and clinical relevance

Although heparin has been a cornerstone of treatment for the prevention of thrombosis, it is limited by its adverse effects and unpredictable bioavailability. Direct thrombin inhibitors are a novel class of drugs that have been developed as an effective alternative mode of anticoagulation in patients who suffer from heparin-induced thrombocytopaenia, and for the management of thromboembolic disorders and acute coronary syndromes. The main disadvantages of the direct thrombin inhibitors are the lack of an antidote or readily available clinical monitoring. The mechanism of action, the properties of direct thrombin inhibitors and their potential to replace currently available anticoagulants are reviewed.