Lethal Heparin-Associated Pulmonary Embolism

Abstract

Thrombocytopenia is a known adverse reaction occurring in some patients receiving heparin. Two different types of heparin-induced thrombocytopenia have been described. Heparin- induced thrombocytopenia type I is a mild thrombocytopenia after 1 to 4 days of heparin therapy, attributed to a direct interaction between heparin and circulating platelets. No specific treatment is necessary. Heparin-induced thrombocytopenia type II is a severe thrombocy topenia mediated by an immunologic mechanism. Type II generally develops after 5 to 10 days of heparin therapy and can be associated with potentially devastating thromboembolic compli cations. The incidence of heparin-induced thrombocytopenia type II is below 3%. Thrombo embolic events are always accompanied by a decrease in the platelet count, however, compli cations in the absence of absolute thrombocytopenia have been reported. Diagnosis of HIT type II is based on clinical features and laboratory studies for the heparin-dependent platelet antibody. Immediate cessation of heparin administration is essential. Several alternative anti coagulant therapies have been studied and have shown promising results when used for this purpose. Two patients undergoing coronary artery bypass surgery are presented in whom pulmonary embolism developed due to heparin-induced thrombocytopenia type II. In both cases, platelet counts were within the subnormal range at the time of the first thromboembolic complication. The clinical, therapeutic, and prognostic implications are discussed.