Inhibition of fibrin deposition as a marker of antithrombotic effect in the thrombus chamber. Thrombogenic devices comprising a 4-mm diameter proximal Dacron graft segment and a 9-mm diameter distal thrombus chamber were deployed into the permanent arteriovenous shunts at 10 minutes after the start of PCA, APC, LMWH, or vehicle (control) infusion. Deposition of fibrin in the 1.27-mL thrombus chamber at 100 mL/minute blood flow rate was determined after 60 minutes of perfusion. (A) The means of fibrin deposition in each treatment dose group are displayed with error bars. All treatments significantly reduced fibrin accumulation by more than 50% but less than 95% in comparison with vehicle-treated controls. All doses of the PCA and enoxaparin doses of 650 μg/kg and above inhibited thrombus formation by more than 75%. (B) The average antithrombotic efficacies of treatments with PCA, APC, or LMWH were calculated as percent inhibition of fibrin deposition, compared with untreated controls, and are shown with the 95% confidence intervals. The antithrombotic efficacies of PCA (83%, n = 15, average dose 4.9 μg/kg) and LMWH (85%, n = 23, average dose: 1006 μg/kg) were comparable.