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Ann Thorac Surg 2005;80:303
© 2005 The Society of Thoracic Surgeons
a Cardiothoracic Surgery, Brody School of Medicine, East Carolina University, Greenville, NC 27858
b Department of Cardiac Surgery, Austin Hospital, HSB-5, Studley Rd, Heidelberg, Melbourne, Victoria, Australia 3084
(Email: motens{at}mail.ecu.edu; brian.buxton{at}austin.org.au).
Heparin-induced thrombocytopenia (HIT) is a potential life threatening complication of heparin therapy, in particular unfractitionated heparin. Heparin is the mainstay of anticoagulation used for cardiopulmonary bypass thanks to its ease of use, rapid monitoring, short half-life, reversibility, and low cost. As many as 50% of patients have measurable heparin-platelet factor 4 antibody titers develop after cardiac surgery using unfractitionated heparin, but only 1% to 3% have observed HIT (a clinicopathologic diagnosis based on clinical findings, fall in platelet count, and measurable heparin-platelet factor 4 antibodies) develop after cardiac surgery. Early re-exposure to heparin in established HIT is a serious risk.
Alternative anticoagulants (such as bivalirudin, which is a direct thrombin inhibitor) have been marketed as alternatives to heparin anticoagulation and have a role in cardiac surgery in proven or suspected HIT. The author outlines their experience in four cases of suspected HIT, based on a fall in platelet count after heparin administration at cardiac catheterization. Experience with bivalirudin in cardiac surgery is limited, and although the authors have demonstrated that in certain cases it can be used relatively safely, there are important issues to note with its use.
Bivalirudin interacts reversibly with thrombin; its half-life is 25 minutes and it requires continuous infusion. Frequent intraoperative monitoring with ecarin clotting time is required, and adjustments are made according to individual patient nomograms. The effect on intraoperative blood loss is not well described. Cessation of the infusion before the end of bypass requires careful planning. Patient temperature at this time is also critical in determining the time taken for the infusion to be enzymatically eliminated and for adequate hemostasis return.
The author has highlighted their use of bivalirudin in these select cases. Heparin-induced thrombocytopenia was not proven, and it is important to remember that there are other important causes of thrombocytopenia, such as glycoprotein IIb/IIIa inhibitors and hemodilution, which may have contributed in the studied cases.
The thrombotic risk associated with HIT is not confined to the intraoperative period, and both preoperative and postoperative anticoagulation with alternative anticoagulants must be carefully planned. Patients should be screened for thrombotic complications.
Use of bivalirudin should be limited to proven cases or where there is a high degree of suspicion. Heparin therapy currently remains the safest and most proven method of anticoagulation in patients without acute HIT and HIT > 100 days previously. When HIT is suspected and timely antibody titer is not available, alternative anticoagulant therapy, such as bivaliruidin, may be used with attention paid to the previously raised issues.
Related Article
Ann. Thorac. Surg. 2005 80: 299-303.
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