High-dose IVIG and usual heparin anticoagulation for urgent cardiac surgery in a patient with severe autoimmune HIT.

A 56-year-old woman required urgent cardiac surgery for Streptococcus mitis mitral valve infective endocarditis complicated by severe autoimmune HIT (aHIT). We reasoned that the combination of high-dose IVIG (to mitigate aHIT antibody-mediated platelet activation in the presence of heparin) together with the high concentrations of heparin attained during cardiac surgery (which typically produce less platelet activation in-vitro versus usual therapeutic heparin concentrations) might prove effective. Accordingly, our patient underwent cardiac surgery with heparin following high-dose IVIG (1g/kg×2), without intra- or postoperative thrombosis. Serial serotonin-release assays, using blood obtained pre-/post-IVIG, showed minimal platelet activation (∼30% serotonin-release) post-IVIG at heparin concentrations typically obtained during cardiac surgery (2-5 U/mL), and significantly less than pre-IVIG serum in heparin's absence (∼85% serotonin-release). In the setting of urgent cardiac surgery, preoperative high-dose IVIG appears to be a reasonable strategy to reduce platelet-activating effects of HIT (including aHIT) antibodies, permitting safe use of standard intraoperative heparin dosing.