Ventricular assist devices (VADs) are surgically implanted mechanical pumps that have a large foreign surface area in direct contact with flowing blood, thereby creating an inherently prothrombotic environment. In a non-randomized study of patients who received heparin-coated and uncoated VADs, there was no difference in the development of anti-PF4/heparin antibodies and thromboembolism between the groups (Koster et al., 2001). In two more recent studies, 10/113 (8.8%) (Schenk et al., 2006, 2007) and 28/358 (7.8%) (Koster et al., 2007) of VAD patients developed apparent HIT. In both studies, the frequency of anti-PF4/heparin antibody formation (by EIA) was over 60%. While these apparent frequencies of clinical HIT (~8%) are among the highest reported in any patient population, it remains unclear how to distinguish true clinical HIT from a patient with cardio-genic shock or other non-HIT explanations for thrombocytopenia who coinciden-tally develop heparin-dependent platelet-activating antibodies (Warkentin and Crowther, 2007).
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