Heparin-induced thrombocytopenia in patients readmitted after open cardiac surgical procedures: A case series

Objectives

Heparin-induced thrombocytopenia (HIT) is an immune-mediated complication that occurs in a small percentage of patients exposed to heparin. Concerns of HIT are particularly high in patients undergoing cardiac procedures requiring cardiopulmonary bypass, as they are exposed to high doses of heparin intraoperatively. Our aim was to identify and assess the hospital courses of patients who were diagnosed with HIT during readmission following cardiac surgery.

Methods

A retrospective review of patients who underwent open cardiac surgical procedures from June 2017 through October 2019 was performed. Of these, we identified patients who were newly diagnosed with HIT upon readmission. HIT positivity was defined as a positive anti-PF4 antibody screening test, plus a positive serotonin release assay.

Results

Of the 2496 patients identified, 13 patients were HIT positive on index admission and were excluded. Of the remaining 2483 patients, 351 were readmitted within 30 days. Six were newly diagnosed with HIT during readmission, 5 of whom presented with thrombotic complications. One patient was readmitted with thrombocytopenia and was started on argatroban; the remaining 5 did not have a significantly lower platelet count on readmission. Of the 12 patients readmitted for venous thromboembolism, 4 tested positive for HIT.

Conclusions

HIT can have a delayed appearance following open heart surgery. Venous thromboembolism appears to be a significant indicator for HIT during readmission, even in the absence of thrombocytopenia. This may support the use of non-heparin anticoagulation for cardiac surgery patients readmitted with thromboembolism until HIT status is determined.

Production of Anti-platelet Factor 4/Heparin Complex Antibodies After Cardiovascular Surgery

To study the production of anti-platelet factor 4 (anti-PF4)/heparin complex antibodies of Ig (immunoglobulin) G/IgA/IgM using enzyme-linked immunosorbent assay (ELISA; heparin-induced thrombocytopenia [HIT] antibodies) in 79 patients undergoing cardiovascular surgery, we employed Δoptical density (OD) as a marker of HIT-antibody production. The ΔODs were calculated from the differences in the ODs using ELISA. Patient were classified into 3 ΔOD ranges: ΔOD ≥ 1.0, ΔOD ≥ 0.4 to <1.0, and ΔOD < 0.4. The underlying disease, time course of the postoperative platelet count, d-dimer level, postoperative brain magnetic resonance imaging (MRI), use of cardiopulmonary bypass and postoperative thrombocytosis were not considered for the 3 ΔOD classifications. None of the 6 patients with ΔOD ≥1.0 and a positive functional assay was diagnosed with HIT due to the absence of HIT-derived thrombocytopenia. In conclusion, HIT-antibody production increased until day 7 after heparin cessation and reached a trace level on day 14. It was demonstrated that HIT-antibody production is in remission unless there is any evidence of a further increase during the second week postsurgery.