HEPARIN COATING OF TANTALUM CORONARY STENTS REDUCES SURFACE THROMBIN GENERATION BUT NOT FACTOR IXA GENERATION

In the present study we used an in-vitro technique to examine initiati on and propagation of blood coagulation at the surface of tantalum cor onary stents exposed to flowing platelet-rich and platelet-free plasma . The time course of factor IXa production at the surface of the stent was not influenced by platelets. In spite of a significant factor IXa production, no thrombin activity was detected when the tantalum stent was exposed to platelet-free plasma; only when the stent was exposed to platelet-rich plasma was extensive thrombin production observed. Th ese findings indicate that tantalum triggers blood coagulation, but th at (adherent) platelets are essential for thrombin generation. Heparin -coated tantalum stents exposed to flowing platelet-rich plasma showed that factor IXa generation was slightly reduced compared with the bar e stent. However, the heparin coating drastically delayed the onset of thrombin generation and largely reduced the steady-state production o f thrombin. We found a clear relationship between the antithrombin bin ding capacity and the antithrombogenic potential of the heparin-coated stents. The mode of action of immobilized heparin is thought to abrog ate thrombin generation by inhibiting thrombin-dependent positive feed back reactions at the surface of the coronary stent. (C) 1998 Lippinco tt-Raven Publishers.