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Thrombogenicity of the Hemobahn/Viabahn in the SFA

Mattias Fischer et al.1 are to be congratulated on their 6-year clinical investigation of the Hemobahn/Viabahn endoprosthesis in the treatment of long chronic lesions of the superficial femoral artery (SFA). It is most refreshing to have an article that follows the outcome of endovascular treatment of the femoropopliteal segment for 2 years. Usually, 5-year data for bypass surgery is required, but trials of 2 years for endovascular procedures are uncommon. It is also reassuring to see other centers achieving similar results to our report in 20032 after several large company-sponsored trials reported extraordinary results with the Hemobahn stent-graft.3 It was unfortunate that our publication was not quoted, as we had similar findings. Ours was the first study to show an acute thrombosis rate that was clinically unacceptable. In our study of the Hemobahn stent-graft for the treatment of 10-cm occlusive SFA lesions, we had a 1-year primary patency rate of only 58% (on an intention-to-treat basis) and a secondary patency rate of 73% in our 54 cases despite a 95% technical success rate. We had a 25% primary occlusion rate in the first 12 months, of which 60% had a completely normal duplex study in the preceding 3 months. We were very disappointed in this outcome and suggested some reasons why this may have occurred.2 A thrombotic predisposition in these patients was investigated, but all had a normal thrombophilia profile apart from 1 case of Factor V Leiden. Fischer et al.1 had a 23% firstyear thrombosis rate, despite the use of clopidogrel and low-molecular-weight heparin (LMWH), treating shorter segments, and not treating to the level of the popliteal. It appears that there is a problem with the Hemobahn/ Viabahn with respect to its thrombogenicity. We strongly disagree with the assertion that these endografts are fully endothelialized. The study by Virmani et al.4 quoted in this article was a trial in the canine model that showed a significantly greater rate of endothelialization compared to grafts in humans, where there is rarely greater that 2 to 3 cm of endothelialization at either end of the graft.5,6,7 Hence, the main thrombogenic factor is the expanded polytetrafluoroethylene (ePTFE) itself. This has been demonstrated in experimental models.8 This problem could potentially be alleviated by the use of heparin bonding9 and denucleation,10 yet it is strange that this has not been addressed in the Viabahn despite many clinicians coming to the same conclusions (personal observation). It is of much concern that Gore has modified the ePTFE in the Excluder because of porosity problems but has not shown a similar concern for the thrombogenicity in the Viabahn. How many more of these kinds of studies will have to be published before these problems are addressed? At present, new-generation self-expanding nitinol bare stents have an equivalent, if not better, outcome in our hands. They also do not occlude collaterals, so patients presenting with reocclusion do not usually have threatened limbs. This has even been confirmed by earlier strong proponents of the Hemobahn in femoropopliteal occlusive disease.11 Even though secondary patency rates are reasonable, the Fischer article has shown that nearly half of stent-grafted limbs will thrombose for no apparent reason despite LMWH, clopidogrel, and close ultrasound surveillance. This is most unsatisfactory and requires addressing.