Heparin-induced platelet activation in sixteen surgical patients: diagnosis and management.

Heparin-induced platelet activation (HIPA) is a syndrome associated with thrombocytopenia, intravascular thrombosis, and arterial emboli. We have evaluated 16 patients for presumed HIPA because of the occurrence of thrombocytopenia or a new thrombotic complication during heparin therapy. In this group, 16 thrombotic events occurred in 10 patients with a mortality rate of 18.8%. Diagnosis was confirmed in vitro by the demonstration of at least 20% platelet aggregation and/or 6% 14C-serotonin release after heparin (0.1 to 3 U/ml) was added to a mixture of patient platelet-poor plasma (PPP, two parts) and aspirin-free donor platelet-rich plasma (PRP, three parts). After heparin was discontinued, seven patients continued to have HIPA in their own PRP although it could no longer be observed in donor PRP. Iloprost, a potent prostacyclin analog that reversibly inhibits platelet activation, completely prevented HIPA and release in all of nine patients. Aspirin, an irreversible cyclooxygenase inhibitor, failed to prevent HIPA in four of these nine patients. In conclusion, HIPA is associated with an extremely high morbidity and mortality rate. Evaluation of the patients' PRP in response to heparin may improve the diagnostic sensitivity of this assay. Aspirin does not reliably prevent HIPA, which suggests participation of thromboxane-independent pathways. Thus, if further exposure to heparin is unavoidable, a more effective platelet inhibitor such as iloprost is required to reliably prevent in vivo HIPA.