Heparin management in a patient with thyroid storm

Management of atrial fibrillation during thyroid storm includes anticoagulation for risk of clot propagation. Physiologic changes that occur in patients with thyroid storm may lead to heparin resistance and inappropriate anticoagulation. Factors contributing to heparin resistance include antithrombin deficiency, increased heparin clearance, and increased levels of factor VIII. We describe a 30-year-old woman who was hospitalized with thyroid storm. She subsequently developed atrial fibrillation, and unfractionated heparin was started. Over the next 4 days, the heparin infusion rate was titrated to an exaggerated dose of 2100 units/hour (33 units/kg/hr) in order to attain a therapeutic response. By hospital day 7, her atrial fibrillation had resolved; the heparin infusion was discontinued, and the patient remained clinically stable with no sequelae. The exact mechanism of heparin resistance in thyroid storm is unknown; however, data have shown a positive correlation between factor VIII and thyroxine levels. This patient had an elevated thyroxine level of 32.5 microg/dl, which suggested that an increased factor VIII level was the probable mechanism of heparin resistance. Recognition of possible heparin resistance in patients with thyroid storm will allow clinicians to promptly identify appropriate interventions to ensure adequate anticoagulation in this high-risk patient population.