Laboratory monitoring of heparin and the combination of heparin and the platelet glycoprotein IIb/IIIa receptor antibody fragment abciximab (c7E3) in patients undergoing percutaneous transluminal coronary angioplasty (PTCA)

Abstract

Background: Previous studies in patients undergoing percutaneous transluminal coronary angioplasty (PTCA) have restricted laboratory monitoring to the activated clotting time (ACT). It remains unknown whether the ACT-prolonging effect of abciximab is clinically equivalent to a comparable degree of anti-coagulation by heparin.

Patients and methods: 30 patients undergoing PTCA received 100 IU of heparin/kg body weight. Another 30 patients received an initial bolus of 70 IU of heparin/kg + abciximab. We determined ACT, laboratory and onsite activated partial thromboplastin time (APTT) and plasma heparin levels.

Results: Despite markedly different preintervention heparin dosing, the ACTs were not significantly different between groups. After termination of PTCA, the median ACTs of both study groups were nearly equivalent (267 vs. 272 s; p = 0.79). The median ACT-prolonging effect of abciximab could be equated with 0.68 IU/ml heparin. Both APTT assays were not suitable for monitoring the anticoagulant effects during PTCA due to their high sensitivity. By contrast, the plasma heparin levels clearly reflected the different heparin doses. The weak correlation (r = 0.23) between ACTs and heparin levels in patients receiving heparin + abciximab was due to excessively prolonged ACTs in six patients (540-1,245 s). These data could be attributed to an unusually high response to abciximab. By contrast, the ACT was a reliable measure of the anticoagulant effect of heparin in patients receiving exclusively heparin.

Conclusions: ACT reflects both heparin and abciximab therapy, whereas heparin levels reflect only heparin dose. The APTT assays were not suitable for monitoring the anticoagulant effects during PTCA.