Understanding the hemostatic effects of recombinant factor VIIa by clot wave form analysis

The monitoring of coagulation-inhibitor bypassing agents, including recombinant factor VIIa (rFVIIa), remains a major issue in the management of clinical hemophilia. Clotting assays using prothrombin time (PT) and measurements of factor VII (FVII) activity do not always reflect the hemostatic effects of treatment. Thrombelastography can be used to observe the global effects of treatment on the overall coagulation process and is especially useful for observing the effects of hemostatic treatment in hemophilia patients with inhibitors. Waveform analysis is another technique for evaluating global hemostatic condition where changes in light transmission during routine clotting assays, such as the activated partial thromboplastin time (aPTT), are measured. We found that waveforms differed between individual patients with severe hemophilia A (FVIII:C < 1.0 IU/dL) with levels of sensitivity at below FVIII:C 1.0 IU/dL. Clot waveforms indicated dose-dependent improvements in clot formation after the addition of rFVIIa to both FVIII-deficient and factor IX (FIX)-deficient plasma. The improvements were further enhanced in the presence of both platelets and synthetic phospholipids, and were more pronounced with FVIII-deficient plasma than with FIX-deficient plasma. It appears that clot waveform analysis provides a very useful means for monitoring hemostasis in hemophilia A patients with inhibitors.