Heparin-Bonded Stent-Graft for the Treatment of TASC II C and D Femoropopliteal Lesions: The Viabahn-25 cm Trial

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1 J ENDOVASC THER 2014;21: CLINICAL INVESTIGATION Heparin-Bonded Stent-Graft for the Treatment of TASC II C and D Femoropopliteal Lesions: The Viabahn-25 cm Trial Thomas Zeller, MD 1 ; Patrick Peeters, MD 2 ; Marc Bosiers, MD 3 ; Johannes Lammer MD 4 ; Klaus Brechtel, MD 5 ; Dierk Scheinert, MD 6 ; Aljoscha Rastan, MD 1 ; Elias Noory, MD 1 ; and Ulrich Beschorner, MD 7 1 Department Angiology, Universitäts-Herzzentrum Freiburg-Bad Krozingen, Bad Krozingen, Germany. 2 Department Cardiovascular Surgery, Imelda Ziekenhuis, Bonheiden, Belgium. 3 Department Vascular Surgery, A.Z. Sint-Blasius, Dendermonde, Belgium. 4 Department Cardiovascular and Interventional Radiology, Medical University Vienna, Austria. 5 Department Radiology, Eberhard Karl s Universität, Tübingen, Germany. 6 Park-Krankenhaus, Leipzig, Germany. 7 CoreLab Bad Krozingen, Germany. Purpose: To confirm the performance and safety of the 25-cm Viabahn endoprosthesis with Propaten bioactive surface when used in the treatment of de novo and/or restenotic TransAtlantic Inter-Society Consensus II C and D lesions of the superficial femoral artery and proximal popliteal artery. Methods: The 25-cm Gore Viabahn Endoprosthesis study (ClinicalTrials.gov identifier NCT ) is a prospective, multicenter, single-arm study that enrolled 71 patients (50 men; mean age years) with lifestyle-limiting claudication (Rutherford class 2 to 4) and lesions longer than 20 cm (mean length cm, range 20 40). The majority of lesions (92.9%) were total occlusions. The primary performance outcome was post-deployment stent length within 610% of the pre-deployment stent length determined angiographically by quantitative vascular analysis. The primary safety outcome was device- and procedure-related serious adverse events occurring within 30 days of the procedure. The patients underwent follow-up examinations at 1 month and 1 year. Results: The median follow-up was 12.3 months (mean ). Nine (12.7%) patients discontinued the study due to different reasons including 2 bypass surgeries. Angiography was available in 60 patients to determine the primary performance outcome, which was met in all cases. Two (2.8%) patients experienced a procedure-/device-related adverse event (dissection) during the 30-day follow-up. Kaplan-Meier estimates for 1-year primary and secondary patency were 67.0% [95% confidence interval (CI) 53.5% to 77.3%] and 96.9% (95% CI 88.0% to 99.2%), respectively. Changes in ankle-brachial index and Rutherford category at 1 and 12 months each showed sustained improvement. Conclusion: This study confirms that the 25-cm Viabahn endoprosthesis acutely performs as intended and is safe when used as indicated in complex femoropopliteal lesions. Oneyear primary and secondary patency rates are satisfying and comparable to historical prosthetic bypass graft outcomes. J Endovasc Ther. 2014;21: This study was supported by W.L. Gore & Associates, Flagstaff, AZ, USA. Thomas Zeller is a member of the Scientific Advisory Board of Medtronic-Invatec, W.L. Gore & Associates, Angioslide, Medtronic/Ardian, Covidien/ev3, and has received lecture fees from Sanofi-Aventis, C.R. Bard, Cordis, Covidien/ev3, Boston Scientific, Straub Medical, Invatec, Biotronik, and Pathway Medical. Johannes Lammer is a member of the Scientific Advisory Board of Abbott Vascular and W.L. Gore & Associates and has received lecture fees from Medtronic, W.L. Gore, and Terumo. The other authors declare no association with any individual, company, or organization having a vested interest in the subject matter/products mentioned in this article. Corresponding author: Prof. Dr. med. Thomas Zeller, Universitäts-Herzzentrum Freiburg-Bad Krozingen, Südring 15, Bad Krozingen, Germany. thomas.zeller@universitaets-herzzentrum.de Q 2014 INTERNATIONAL SOCIETY OF ENDOVASCULAR SPECIALISTS doi: / r.1 Available at

2 766 STENT-GRAFTS IN TASC II C/D FEMOROPOPLITEAL LESIONS J ENDOVASC THER Zeller et al. 2014;21: Key words: peripheral artery disease, superficial femoral artery, stenosis, occlusion, angioplasty, covered stent, stent-graft, heparin bonding, polytetrafluoroethylene, patency The prevalence of lower extremity peripheral artery disease (PAD) in the United States and Europe is as high as 19% in the general population and 29% in patients older than 70 years. 1,2 Lesions of the femoropopliteal segment are the most common cause of symptomatic PAD, 3 and endovascular treatment of femoropopliteal lesions up to 15 cm has been recommended by various international societies and consensus conferences. 4 6 Randomized controlled trials comparing percutaneous transluminal angioplasty (PTA) to primary stenting in short lesions of the superficial femoral artery (SFA) have demonstrated the superiority of primary stent placement. 7,8 Recently, drug-coated balloons have shown almost equivalent results to bare metal stents in TransAtlantic Inter-Society Consensus (TASC) II A and B lesions, 9 12 whereas drug-eluting stents were superior to bare metal stents in the same indication. 13 With advancing technologies, endovascular recanalization of long lesions (TASC II C and D 4 ) has become technically feasible in a large percentage of patients, 14 but the durability of PTA in long SFA lesions remains poor. 15 Primary stent placement has shown promising results in a single-arm study, 16 and the subgroup analysis of lesions longer than 15 cm in the Zilver PTX single-arm trial using a paclitaxel-eluting stent suggested even better results. 17 Just recently, the VIASTAR trial reported superior outcomes treating TASC II C and D femoropopliteal lesions using expanded polytetrafluoroethylene (PTFE) covered stents compared to bare metal nitinol stents. 18 The present study evaluated the safety and deployment of the 25-cm Viabahn endoprosthesis with a heparin (Propaten) bonded to the PTFE and the midterm technical and clinical performance of the device in femoropopliteal lesions longer than 20 cm (TASC II C and D). Study Design METHODS The 25-cm Viabahn trial was designed as a prospective, sponsor-initiated, single-arm, multicenter study to confirm the safety and performance of the 25-cm heparin-bonded Viabahn stent-graft (W.L. Gore & Associates Inc., Flagstaff, AZ, USA) when deployed in the SFA and proximal popliteal artery. The initial purpose of the study was to supply safety data for submission to the United States Food and Drug Administration (FDA) in support of a pre-market application for the 25-cm version of the already approved Viabahn endoprosthesis with Propaten bioactive surface. A further goal of the study was to gather longitudinal clinical and radiographic data through 3 years post procedure. The study complied with European Standard ISO 14155, Clinical Investigation of Medical Devices for Human Subjects, and the recommendations guiding physicians in biomedical research involving human subjects adopted by the 18th World Medical Assembly, Helsinki, Finland, 1964 and later revisions. The study was approved by the local ethics committees of the 7 participating investigational sites in the European Union. Independent study monitoring and data management was performed by Medpace Strategic Consultants, B.V., Vaals, The Netherlands. Angiograms and radiographs were evaluated by CoreLab Bad Krozingen, Germany. The trial was registered on the National Institutes of Health website (ClinicalTrials.gov; identifier NCT ). Patient Enrollment The major inclusion criteria were symptomatic PAD (Rutherford categories 2 to 4: moderate to severe claudication and rest pain); de novo or restenotic (excluding instent) atherosclerotic stenosis or occlusion of the SFA and proximal popliteal artery (limited distally to the middle of the femur condyle);

3 J ENDOVASC THER STENT-GRAFTS IN TASC II C/D FEMOROPOPLITEAL LESIONS ;21: Zeller et al. TABLE 1 Baseline Characteristics of the 71 Study Patients and Procedure Details Age, y Men 50/71 (70.4%) Smokers Current 37/71 (52.1%) Former 21/71 (29.6%) Diabetics 23/71 (32.4%) Type I insulin dependent 1/71 (1.4%) Type II insulin dependent 9/71 (12.7%) Non-insulin dependent 13/71 (18.3%) Hypertension 56/71 (78.9%) Hypercholesterolemia 45/71 (63.4%) CAD 24/71 (33.8%) Stroke 4/71 (5.6%) Renal insufficiency 7/71 (9.9%) COPD 4/71 (5.6%) Rutherford category 2 Moderate claudication 11/67 (16.4%) 3 Severe claudication 50/67 (74.6%) 4 Ischemic rest pain 6/67 (9.0%) Treated limb Left 40/71 (56.3%) Right 31/71 (43.7%) Lesion characteristics Stenosis 5/70 (7.1%) Occlusion 65/70 (92.9%) Lesion location in SFA Proximal 58/71 (81.7%) Mid 68/71 (95.8%) Distal 63/71 (88.7%) Lesion length, cm (20 40) Devices implanted 1 30/71 (42.3%) 2 41/71 (57.7%) Days to discharge 1 9/71 (12.7%) 2 34/71 (47.9%) 3 9/71 (12.7%) 4þ 19/71 (26.8%) Continuous data are presented as the means 6 standard deviation (range); categorical data are given as the counts (percentage). CAD: coronary artery disease, COPD: chronic obstructive pulmonary disease, SFA: superficial femoral artery. lesion length 20 cm (TASC II C and D); patent or successfully treated iliac artery inflow; a visible SFA stump of at least 1 cm in total occlusions; and outflow of at least 1 tibial artery. The major exclusion criteria were untreated inflow lesions, any previous stents or surgery in the target artery, serum creatinine.2.5 mg/dl, septicemia, and known intolerance to heparin, antithrombotic study medications, or contrast agents. Patients were required to sign an informed consent document before the procedure. Final enrollment in the study occurred after successful wire traversal of the target lesion. Between 2011 and 2012, 71 patients (50 men; mean age years) were enrolled. The baseline characteristics are summarized in Table 1. The majority (74.6%) of patients suffered from severe claudication. Almost all lesions were total occlusions (92.9%). Mean lesion length was cm (range 20 40). Intervention All subjects received treatment with the 25- cm Viabahn stent-graft with Propaten bioactive surface, at times overlapped with additional Viabahn models (lengths of 2.5, 5, 10, 15, or 25 cm) at the investigator s discretion based on the total lesion length (20 cm). Most patients started taking clopidogrel 1 or 2 days before the index procedure; for those who did not, a 600-mg loading dose was given prior to or during the procedure. The intervention was done percutaneously in almost all cases with a crossover access under local anesthesia using 6- to 8-F sheaths. All patients received 5000 units of heparin during the procedure. Angiography of the target lesion was performed in 2 planes before and after intervention. Moreover, cineangiography without contrast was required to show the Viabahn stent-graft(s) before and after deployment. After treatment, patients received 100 mg aspirin daily for life and 75 mg/d of clopidogrel for at least 6 months. Definitions The primary performance outcome measure was successful completion of the assigned treatment and post-deployment length of the first deployed 25-cm heparin-bonded Viabahn endoprosthesis within 610% of its pre-deployment length. Successful completion of the assigned treatment was a composite of the investigator s ability to successfully cover the target lesion with the device and attain a post-deployment residual stenosis of

4 768 STENT-GRAFTS IN TASC II C/D FEMOROPOPLITEAL LESIONS J ENDOVASC THER Zeller et al. 2014;21: TABLE 2 Performance Outcomes Stent length within 10% of pre-deployment length 58 (100.0%) Length difference, cm (n¼58)* , 0.34 ( 2.02 to 0.77) Covered target lesion 71/71 (100.0%) Post-deployment residual stenosis,30% 55/69 (79.7%) Continuous data are presented as the means 6 standard deviation, median (range); categorical data are given as the counts/sample (percentage). * Between post-deployment and pre-deployment.,30% within the treated segment. The investigator determined if the device was successfully deployed in the target lesion, while the independent core laboratory determined the post-deployment residual stenosis and calculated post-deployment stent elongation. In order for a subject s treatment to be considered a failure of the primary performance measure, the procedure had to either fail the successful completion of the assigned treatment composite or fail the post-deployment residual stenosis,30% criterion, or both. The primary safety measure was the proportion of subjects who experienced deviceor procedure-related serious adverse events within 30 days post-procedure. Secondary outcome measures included changes in ankle-brachial index (ABI) and Rutherford category from baseline to values at 1, 12, 24, and 36 months and estimates of the primary and secondary patency rates, freedom from target lesion revascularization (TLR), freedom from device fracture, and freedom from a composite of death, target vessel revascularization (TVR), and amputation (above metatarsals) at the same time points. Primary patency was defined as no restenosis or occlusion within the treated lesion, while secondary patency referred to restoration of patency by TLR after restenosis/ occlusion. Restenosis is based on duplex ultrasound measurement of a.2.5 peak systolic velocity ratio as assessed by the core laboratory. 19 Statistical Analysis Continuous data are presented as the means 6 standard deviation; categorical data are given as the counts/sample (percentage). Primary and secondary patency and freedom from TLR and device fracture were estimated using the Kaplan-Meier product-limit method, and the rates are presented with the 95% confidence intervals (CI). Calculations were performed with SAS (version 9.2; SAS Institute Inc., Cary, NC, USA). RESULTS According to the investigators, all study devices were deployed successfully; the core laboratory confirmed that all target lesions were covered with the 25-cm Viabahn and additional Viabahn models as needed (Table 2). The median follow-up was 12.3 months (mean ). Nine (12.7%) patients discontinued the study before the 1-year evaluation: 3 were lost to follow-up, 2 expired, 2 had a surgical bypass, 1 had an amputation above the ankle, and 1 withdrew consent. Thirteen subjects were missing some imaging elements (pre-deployment images in 4, both pre- and post-deployment images in 7, postdeployment images in 2) and 2 subjects had images that were inadequate for determining residual stenosis. Primary Outcome Measures For evaluation of the primary performance measure, 11 patients had insufficient imaging for evaluation of both core laboratory defined components, which left 60 evaluable subjects for this composite measure of successful lesion coverage and no significant foreshortening. The device was successfully delivered to cover the target lesion in all 60 subjects, and all 60 test devices (25-cm Viabahn) had

5 J ENDOVASC THER STENT-GRAFTS IN TASC II C/D FEMOROPOPLITEAL LESIONS ;21: Zeller et al. SFA, both of which were successfully treated with the deployment of an additional Viabahn device. Two (2.8%) of the 6 subjects not having a 30-day visit to assess serious adverse events returned for an out-of-window, unscheduled visit, and adverse event data were collected from them (no events). The duration of hospitalization is shown in Table 1. Figure 1 Kaplan-Meier estimate of freedom from device- or procedure-related serious adverse events. Patients at risk are given per interval; the standard error did not exceed 10% at 1 year. post-deployment stent lengths within 610% of their pre-deployment lengths. Of the 58 deployed devices with evaluable images for estimation of the residual stenosis, 44 (75.9%) had a post-procedure residual stenoses 30% when measured by the core laboratory; however, 14 (24.1%) cases had residual stenoses.30% and 50%, indicating technical failure. Half of these 14 cases with a residual stenosis.30% had a residual stenosis between 31% and 35%. The highest postprocedure residual stenosis measured by the core laboratory was 50%. Information to assess the primary safety measure was available in 65 (91.5%) of the 71 subjects; of these, 63/65 (96.9%) were free from device- or procedure-related serious adverse events within 30 days post-procedure (Fig. 1). Two patients had dissections of the Secondary Outcomes Table 1 shows the distribution of Rutherford categories at baseline. Mean ABI at baseline was (range ) and increased to (range ) at discharge (p,0.001). Table 3 summarizes the changes in ABI and Rutherford category at 1 and 12 months, with a sustained improvement of clinical outcomes throughout 1 year. Kaplan-Meier estimates for 1-year primary (Fig. 2A) and secondary (Fig. 2B) patency were 67.0% (95% CI 53.5% to 77.3%) and 96.9% (95% CI 88.0% to 99.2%), respectively. Primary patency did not differ significantly (p.0.05) between patients with a single 25- cm stent-graft and those with overlapped devices (Fig. 2C). Primary patency data stratified to lesion length are given in Table 4. Residual stenosis post-deployment did not affect the 1-year patency and safety outcomes. Kaplan-Meier analysis of primary and secondary patency at 12 months as a function of post-procedure stenosis 30% or.30% indicated no differences in primary, assisted primary, or secondary patency rates between the groups (data not shown). The TABLE 3 Changes in ABI and Rutherford Category at 1 Month and 1 Year Changes in Follow-up 1 Month 12 Months Ankle-brachial index ( 0.5 to 0.8) (n¼59) ( 0.7 to 0.8) (n¼54) Rutherford category 4 3/59 (5.1%) 2/56 (3.6%) 3 36/59 (61.0%) 25/56 (44.6%) 2 12/59 (20.3%) 14/56 (25.0%) 1 2/59 (3.4%) 10/56 (17.9%) 0 6/59 (10.2%) 3/56 (5.4%) 1 0/59 (0.0%) 2/56 (3.6%) Continuous data are presented as the means 6 standard deviation (range); categorical data are given as the counts/ sample (percentage).

6 770 STENT-GRAFTS IN TASC II C/D FEMOROPOPLITEAL LESIONS J ENDOVASC THER Zeller et al. 2014;21: Figure 2 Kaplan-Meier estimates of (A) primary and (B) secondary patency through 1 year. Patients at risk are given per interval; the standard error did not exceed 10% at 1 year. (C) Estimate of primary patency in patients with a single 25-cm stent-graft vs. those with overlapped devices. Patients at risk are given per interval; the standard error did not exceed 10% at 8 months for the overlap group and 10 months for the no overlap group. adverse event profiles for both groups were comparable as well; Kaplan-Meier analysis estimated the freedom from serious deviceor procedure-related adverse event rate at 12 months to be 83.3% for subjects with postprocedure residual stenosis.30% compared to 76.7% for subjects with residual stenosis 30% (p.0.05). The Kaplan-Meier estimate of freedom from TLR at 1 year was 78.2% (95% CI 65.9% to 86.5%; Fig. 3A). TLR was necessary in 15 occlusions, 2 stenoses, and 2 patients with clinical symptoms without specifying the reason. Freedom from device fracture through 30 days (n¼49) and 12 months (n¼55) was 100%. Freedom from a composite of death, TVR, and amputation (Fig. 3B) was 94.2% (95% CI 85.3% to 97.8%) and 71.8% (95% CI 59.4% to 81.0%) at 30 days and at 12 months, respectively. One TABLE 4 Primary Patency Stratified by Lesion Length at 1 and 12 Months Range of Stent-Graft Length, cm Time After Treatment, mo Patients at Start of Interval Events During Interval* Patency, % 20 23, (2) 92.9% (74.3% to 98.2%) (11) 57.8% (36.6% to 74.1%) 24 29, (0) 100% (100% to 100%) (3) 78.8% (47.3% to 92.7%) 30 40, (0) 100% (100% to 100%) (6) 70.0% (45.1% to 85.3%) The Kaplan-Meier patency estimate is presented with the 95% confidence interval in parentheses. * Number in parentheses represents cumulative events or censored observations through the end of the interval.

7 J ENDOVASC THER STENT-GRAFTS IN TASC II C/D FEMOROPOPLITEAL LESIONS ;21: Zeller et al. Figure 3 Kaplan-Meier estimates of (A) freedom from target lesion revascularization and (B) freedom from a composite of death, TVR, and major amputation. The standard error did not exceed 10% at 1 year. patient with a patent Viabahn stent-graft underwent major amputation above the ankle due to disease progression. DISCUSSION The purpose of the present study was twofold: first, to evaluate the technical performance and safety of the 25-cm long version of the FDA-approved heparin-bonded eptfe-covered Viabahn endoprosthesis; second, to assess the midterm technical and clinical outcome in patients with symptomatic PAD and long lesions of the SFA and proximal popliteal artery (TASC II C and D lesions). With 93% of the lesions being total occlusions and a mean study lesion length of 26.5 cm, this study investigated the most challenging femoropopliteal lesion cohort ever prospectively examined. The recently published VIASTAR trial compared the performance of the 15-cm heparin-bonded Viabahn endoprosthesis with bare metal nitinol stents (mean lesion lengths of cm vs cm, respectively) in femoropopliteal lesions at 1 year. 18 The primary patency rate in the present study (67.0%) was lower than the VIASTAR Viabahn cohort (78.1%) but higher than the 53.5% of the bare metal stent cohort. However, secondary patency rates were slightly higher in the current study as compared to the Viabahn cohort (96.9% vs. 89.9%) and the bare metal nitinol stent cohort (75.2%) in the VIASTAR trial. 18 Contrary to these promising outcomes, Kuhan et al. 20 reported disappointing results for the heparin-bonded Viabahn stent-graft when used for bailout after failed balloon angioplasty in TASC C and D lesions with a mean length of cm. In their observational study involving 33 limbs (64% of them in critical limb ischemia), the median primary patency was only 5 months. Whether this limited patency was related to the patients critical limb ischemia, including impaired tibial outflow, remains uncertain. In the subgroup analysis of the VIASTAR trial of lesions 20 cm, the 1-year primary patency decreased slightly to 73.3% in the Viabahn cohort but dramatically to 33.3% in the nitinol stent cohort. Finally, the outcome of the present study is in line with the result of the subgroup of lesions.20 cm of the VIPER single-arm trial, which had a 70% 1-year primary patency. 21 In the current study, it was surprising that the lowest primary patency rate (57.8%) was in the shortest lesion subgroup (20 23 cm) compared to the more robust 78.8% in the 24- to 30-cm group and 70% in the.30 cm cohort. It could be the effect of low numbers or that the operators tried to cover the lesion with a single 25-cm-long stent-graft to avoid placing a second device. This might have resulted in incomplete coverage of the entire diseased vessel segment, with potential suboptimal stent-graft expansion at the edges, a phenomenon that has been identified as predictive of restenosis. 21 On the other hand, a residual stenosis.30% after Viabahn implantation, frequently seen in severely calcified vessels, did not negatively affect the outcome, which leads to the conclusion that the use of the stent-graft in potentially

8 772 STENT-GRAFTS IN TASC II C/D FEMOROPOPLITEAL LESIONS J ENDOVASC THER Zeller et al. 2014;21: eccentric calcified lesions is feasible and as efficient as in fibrotic lesions that are more likely to allow proper device expansion. A clinically-driven TLR rate of 21.8% at 1 year in our study resulted in sustained clinical improvement reflected in the ABI and Rutherford categories, in line with the findings of the VIASTAR trial (15.4% Viabahn vs. 23% for bare stents). 18 The 1-year freedom from TLR in another prospective single-arm study with bare nitinol stents in long SFA lesions was only 68.2%. 16 How does the study compare to the performance of drug-releasing devices in long femoropopliteal lesions? The long lesion (.15-cm) subgroup of the Zilver PTX singlearm trial with a mean lesion length of cm demonstrated a 1-year primary patency rate of 77.6% and a clinically-driven TLR rate of 14.6%. 17 Regarding paclitaxelcoated balloons, a recently published retrospective propensity score based analysis of femoropopliteal lesions.10 cm, including 131 drug-coated balloon patients with a mean lesion length of mm (range ), has shown almost similar outcomes in terms of patency and freedom from TLR comparing the IN.PACT drug-coated balloon to the Zilver PTX drug-eluting stent. At 1 year, the primary patency rate was 76.1% and freedom from TLR was 84.4% for the drugcoated balloon. 22 International consensus and guideline documents recommend that femoropopliteal lesions of the kind investigated in the present study be treated primarily with bypass surgery. 4 6 However, the endovascular treatment of PAD has the advantage of low morbidity and mortality, early recovery, and the potential for outpatient delivery. Bypass surgery with venous conduits must still be considered as the gold standard when comparing primary patency rates. However, the high secondary patency rate of 96.9% in the present study demonstrates that similar results compared to surgery can be achieved at a low procedural risk. In the present study, we observed no severe complication requiring surgery or prolonged hospital stay, no procedure-related deaths, and no study limb amputations. Thus, the overall risk compared to surgery seems to be less. 3,23 In the event that no vein is available or the vein is being preserved for aortocoronary bypass surgery in coronary artery disease patients, synthetic above-knee bypass grafts in the femoropopliteal segment have a lower 1-year patency rate (76%) as shown in a randomized controlled trial. 24 Compared to bare nitinol stents, covered stents have the advantage of no ingrowth of neointimal tissue. However, graft thrombosis has been observed in former trials as well as in the present study. 18,20 It remains a concern that acute occlusion of long covered stents may result in limb-threatening acute limb ischemia. In this study, however, only one patient underwent major amputation above the ankle due to disease progression. An appropriate anticoagulation and antiplatelet regimen after Viabahn implantation is still uncertain, particularly as pertains to the duration for the second antiplatelet drug. In the present study, all patients were on an antithrombotic regime of aspirin (100 mg/d) for life and clopidogrel (75 mg/d) for at least 6 months, which may be necessary to achieve a low thrombosis rate. The Viabahn stent-graft used in this study had covalently bound heparin on the luminal surface of the eptfe graft, 24 which was shown in the Scandinavian Propaten trial to prolong the primary patency rate significantly compared to bare eptfe grafts at 1 year. 25 Although most of the endoprostheses were placed into the distal SFA and proximal popliteal artery, vessel segments exposed to the most severe external forces during knee motion, 26 no radiographically visible stent fractures were found in the present study, confirming the results of the VIASTAR trial. 18 Limitations The limitation of the study is its single-arm design; a randomized controlled trial compared to bypass surgery would have been more robust. However, the background of the study was primarily to collect safety data for FDA clearance of the longer version of the already approved heparin-bonded eptfe-covered Viabahn endoprosthesis. Conclusion The present study investigating the performance of the 25-cm-long Viabahn endopros-

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