The treatment of peripheral arterial disease has undergone a sea change in the last decade from invasive open bypass to percutaneous revascularization, thanks to the availability of new technologies. Acute procedural success rates have significantly improved with the availability of chronic total occlusion (CTO) traversal and reentry devices. Midterm results have also improved, chiefly due to endoluminal stents.

Percutaneous transluminal angioplasty (PTA) has been shown to be effective for short (≤ 4 cm) lesions, but primary patency rates are poor for longer lesions, occlusions, calcified vessels, chronic limb ischemia (CLI), and compromised distal vessel runoff.1-4 For moderatelength lesions (5–10 cm), recent studies have demonstrated improved clinical outcomes with bare-nitinol stents (BNS) compared with PTA. BNS address the problems of flow-limiting dissections and early recoil, but at the expense of exaggerated neointimal hyperplasia and resultant in-stent restenosis (ISR).5-9 Treatment of longer-length lesions with BNS has led to the vexing problem of stent fractures, which have been shown to negatively impact patency rates.10,11 Moreover, most studies of BNS for longer lesions have consistently demonstrated reduced primary patency rates.12-15

To overcome the limitations of BNS for longer lesions, several investigators have reported promising results using endoluminal stent grafts.16-23 The role of stent grafts and BNS for long superficial femoral artery (SFA) disease will be reviewed in detail, particularly in those patients with TASC II D lesions.

TASC II CLASSIFICATION

To guide the therapy of patients with peripheral arterial disease, the TransAtlantic Inter-Society Consensus Document on the Management of Peripheral Arterial Disease (TASC) was published in January 2000. This document was updated in 2007 (TASC II).2 The TASC II classification for femoropopliteal disease (Table 1) recommends bypass surgery for type D lesions, which include CTOs of the common femoral artery or SFA > 20 cm involving the popliteal artery, and for CTOs of the popliteal artery and proximal trifurcation vessels. Although several randomized trials have confirmed superior patency rates for above-knee femoropopliteal bypass (AK-FPB) using greater saphenous vein compared with prosthetic grafts, polytetrafluoroethylene (PTFE) grafts are still widely used today for the AK position to allow preservation of the greater saphenous vein for future coronary artery bypass. Other reasons include lack of vein conduit and previous studies demonstrating equivalence of results.24-28

Limitations of open bypass surgery include the need for general anesthesia, longer length of hospital stay, lack of vein conduit, and greater morbidity, particularly in patients presenting with CLI. For example, in the PREVENT III trial for CLI patients undergoing open bypass surgery, 17.4% of patients experienced major morbidity at 30 days, including 4.2% graft occlusion, 4.7% myocardial infarction, 1.7% stroke, 3.4% infection, 1.8% major amputation, and major wound complication in 5.2%.29 Primary graft patency at 1 year was only 61.5%, and event-free survival was 50%. Surgical bypass failure often results in acute limb ischemia, whereas endovascular procedures usually return patients to their preintervention symptom state.30 Hence, many of these prohibitive surgical candidates are only eligible for treatment by endovascular methods.

BARE-NITINOL STENTS

Randomized Trials
Nitinol stents have become standard therapy for femoropopliteal disease due to their ability to tolerate the multiple mechanical forces at play in the hostile femoropopliteal bed and because of their ability to seal dissections and resist elastic recoil. In the US, the LifeStent (Bard Peripheral Vascular, Inc., Tempe, AZ) and EverFlex (Covidien, Mansfield, MA) are currently the only FDA-approved BNS, although other BNS are expected to gain approval soon. Several randomized BNS trials have recently been reported (Table 2). With the exception of the FAST trial, stenting provided superior patency rates compared with PTA.16-23 The SUPER SL and VIBRANT trials showed no significant differences between different stent types.31,32 Although these studies provide convincing evidence of the superiority of stenting over PTA, they are mostly limited to relatively short TASC A and B lesion subsets.

Nonrandomized Trials in Long SFA Disease
Several nonrandomized retrospective studies have been published evaluating bare-metal stents, some of these in longer lesions. DURABILITY-200 reported a 1-year primary patency rate of 64.8% in 100 TASC II C and D patients, with a mean lesion length of 24.2 cm.33 Hu et al reported their single-center retrospective study on 165 limbs in 138 patients treated with BNS, with a mean lesion length of 20.35 ± 9.46 cm (range, 10–32 cm) using 6-mm-diameter devices exclusively; 25.5% were TASC II B, 61.6% were TASC II C, and 51% were TASC II D lesions.34 They reported remarkable primary patency rates of 92%, 78% and 62% at 1, 2, and 3 years but excluded patient lesions extending into the popliteal artery, and did not report on number of limbs at risk at each time.

Schoenefeld et al reported an 83.6% primary patency rate at a mean follow-up of 21 months in 103 patients who were treated with BNS using the Protégé EverFlex (Covidien).35 The mean stent length was 15 cm. Lesions were classified as 36% TASC II C and 8% TASC II D, with a 4.7% overall stent fracture rate; however, lesion measurement methods were not listed. Baril et al specifically examined the outcomes of endovascular interventions in 74 patients (79 limbs) with TASC II D lesions.36 Patients presented with CLI in 71% of cases, including 53% with tissue loss. The mean lesion length was 18.8 cm, 50.6% had single-vessel runoff, and 48% had stents placed in the popliteal artery. Primary patency at 12 and 24 months was 52.2% and 27.5%, respectively. The number of patients who underwent stenting is not listed, precluding evaluation of stent patency, which may explain the poor primary patency rates. Twenty-five percent of patients died during the 1-year follow-up period, underscoring the advanced comorbidity of patients presenting with TASC II D lesions.

The outcomes of consecutive nonrandomized patients with TASC II C and D SFA disease was reported by Dosluoglu et al in a single-center, retrospective analysis.37 One hundred twenty-seven patients underwent AK-FPB (46 patients), PTA/BNS (49 patients) for TASC II C lesions, and PTA/BNS (44 patients) for TASC II D lesions. SMART stents (Cordis Corporation, Bridgewater, NJ) were employed. Mean lesion occlusion and stented lengths were 9.9/24.3 cm and 26.6/30 cm in TASC II C and D lesions, respectively. Twelve- and 24-month primary patency rates were 83%/80% and 54%/28% for the two groups, and the AK-FPB group patency rates were 81% and 75%, respectively. Despite the worse patency rates for TASC II D patients, the limb salvage rates were similar (88%, 88%, and 95% in for TASC II C, TASC II D, and AK-FPB groups, respectively).

The Zilver PTX (Cook Medical, Bloomington, IN) single- arm, real-world registry included 787 patients with a mean lesion length of 10 cm, in which 22% had lesion lengths > 15 cm, and 14% had ISR. Overall freedom from target lesion revascularization was 91.1% at 1 year and 84.3% at 2 years. Subgroup analysis, however, showed a 1-year primary patency of 78% for ISR and 77% for long lesions (mean lesion length, 22.4 cm).38 This study, like the others utilizing BNS for long lesions, demonstrates the inverse relationship of primary patency with increasing lesion length. Other studies have confirmed these findings of inferior patency results in TASC II D lesions.12-15

Stent Fracture
Although BNS provided an improvement in patency rates compared with PTA, it was at the cost of ISR due to proliferative intimal hyperplasia and stent fracture. This latter problem first came to light during the SIROCCO trials, in which 6-month fracture rates of 27% and 17% were observed. Scheinert et al followed three different BNS with serial x-rays.10 Stent fractures were documented in 37% of treated limbs. Increasing stent lengths and vessel calcification predicted stent fracture (risk ratio, 5.55 for stent length > 160 mm; risk ratio, 3.91 for severe calcification), and primary patency was 41.1% versus 84.3% in those with and without fractures.

Iida et al examined the influence of stent fracture on long-term patency in 333 limbs treated with Luminexx (Bard Peripheral Vascular, Inc.) or SMART stents.11 Primary patency at 1 year was 68% in those with stent fractures versus 83% in those without; fractures were found to be more common in CTOs and longer lesion lengths. The BNS group in the VIBRANT randomized controlled trial of the GORE® VIABAHN® Endoprostheses (W. L. Gore & Associates, Flagstaff, AZ) versus BNS documented an overall stent fracture rate of 30.8% and 42.9% in lesions > 15 cm in the BNS group, with a trend toward lower patency compared with the stent graft group.32

COVERED STENT GRAFTS

Randomized Trials
Compared with BNS, covered stent grafts create a barrier to the in-growth of neointimal tissue and exclude plaque and thrombus from the arterial lumen. The GORE® VIABAHN® Device, formerly known as Hemobahn, is the only FDA-approved covered stent for use in the SFA. It is composed of a 100-μm thick expanded PTFE graft with a single nitinol wire and without interconnecting struts, imparting great flexibility and fracture resistance. It is available in lengths of 2.5, 5, 10, and 15 cm in the US and 25 cm outside the US. It was approved in the US in June 2005, and the new design incorporating a heparin-bound endoluminal surface was approved in September 2007, and a laser-cut proximal contoured edge was approved in January 2009. Several single-center studies have reported very good primary patency rates with the GORE® VIABAHN® Device, particularly in longer lesion subsets, and documented that primary patency was independent of lesion length.

Randomized studies using the non–heparin-bonded GORE® VIABAHN® Device are summarized in Table 3. Kazemi et al documented a 90% primary patency rate with the GORE® VIABAHN® Device at 1 year versus 57% in a group treated with the SilverHawk plaque excision atherectomy device (Covidien), despite a 50% adjunctive stent rate in the atherectomy group (however, this is not included in Table 3 because there were < 30 limbs).43 Kedora et al and McQuade et al reported the 2- and 4-year results of a single-center, prospective, randomized controlled trial of the GORE® VIABAHN® Device versus a prosthetic AK-FPB in 86 patients (100 limbs).42,44 The mean artery length treated by the GORE® VIABAHN® Device was 26 cm. There were no differences in patency or limb salvage rates, and 15% of patients were TASC II D. These remarkable patency rates were achieved without clopidogrel, now considered standard pharmacotherapy.

Saxon et al randomized 197 patients to the GORE® VIABAHN® Device versus PTA in a multicenter trial of lesions up to 13 cm in length (mean length, 7 cm).41 Patients received aspirin, as clopidogrel was not yet available. The 1-year primary patency rate was 65% in the stent graft group versus 40% in the PTA group. Patency rates were reported for the limb, not lesion, and defined failure as a peak systolic velocity ratio (PSVR) of > 2. Five of nine stent grafts > 12 cm were patent versus one out of six in the PTA group. TASC classification was not reported.

The VIBRANT trial is a multicenter, randomized study of the prior GORE® VIABAHN® Device (without heparin, contoured proximal edge; 5-mm device sizes available) versus BNS (multiple brands) in 148 patients (Rutherford classes 1–5), with a primary endpoint of primary patency at 3 years.32 The mean lesion lengths were 19 and 18 cm, 40% were CTOs, and 62.5% of lesions demonstrated moderate to severe calcification (primarily TASC C and D lesions). Both groups had disappointing primary patency rates of 53% and 58%, respectively, but there were important differences in the patterns of restenosis: 93% of failed BNS had diffuse ISR versus focal edge restenosis in 87% of the failed GORE® VIABAHN® Devices (Figure 1). This may explain why the GORE® VIABAHN® Device patients with restenosis with a PSVR > 3 had preserved resting ankle-brachial indexes of 0.93 versus 0.76 in the BNS group, and only 36% of these patients had claudication versus 71% of the BNS patients.

Nonrandomized Trials
Table 4 summarizes several of the nonrandomized studies employing the GORE® VIABAHN® Device. Early reports did not specify TASC criteria (TASC I not published until 2000), and many used short duration (≤ 1 month) dualantiplatelet therapy, some with aspirin alone. Lammer et al examined 80 limbs with a mean device length of 13.1 cm; 62% were > 10 cm, and primary patency was 79% at 1 year with a 93% secondary patency rate.16 Jahnke et al reported a primary patency rate of 78%, with a mean lesion length of 10.9 cm in 52 patients, demonstrating patency independent of lesion length.17 Fischer et al documented a 1-year primary patency rate of 78% in 60 limbs with 87%, occlusions with a mean lesion length of 11 cm.19 The 1- and 6-year primary patency rates were 80% and 57%, respectively.

Saxon et al reported on 87 limbs, of which, 81 were TASC II C and D lesions with a mean lesion length of 14 cm. The 1-year primary patency rate was 76%, and the secondary patency rate was 93%, with a lower patency rate in the 5-mm devices. Primary patency was independent of lesion length and type (stenosis vs occlusion). Further, 3.6% developed graft occlusion, and only one patient developed acute limb ischemia that required bypass. Alimi et al reported a similar 1-year patency rate of 74% and a 3-year patency of 71% in 102 limbs with a mean lesion length of 12 cm.21 Twentythree limbs were TASC D lesions.

A more recent report from Farraj et al confirmed a 1-year primary patency rate of 80% in 30 patients with claudication, with a mean lesion length of 15.4 cm.54 The authors avoided implants in heavily calcified vesvessels resistant to dilatation and did not implant any 5-mm devices. Only one patient with stent thrombosis presented with acute limb ischemia, which was treated with bypass.

STUDIES EVALUATING THE CURRENT GENERATION OF THE GORE® VIABAHN® DEVICE

Despite the very long lesion lengths treated in VIBRANT, the primary patency rate for the GORE® VIABAHN® Device fell below the range reported in most series. A few recent studies sought to assess the effects of the new proximal contoured edge and heparin bonding in this device. The proximal contoured edge allowed for improved device apposition with less infolding, resulting in better accommodation of oversizing and improved flow dynamics, with the hope of reducing the incidence of proximal edge stenosis. The heparin bonding was added to reduce the risk of stent graft thrombosis and improve patency, as has been demonstrated in expanded PTFE grafts used in surgical bypass procedures.55-58

VIPER was a prospective, multicenter trial that utilized the new GORE® VIABAHN® Device (Figure 2) in 80 of 120 patients, with a mean lesion length of 19 cm, 56% being CTOs and 61% of lesions having moderate-to-severe calcification.51 The preliminary 1-year overall primary patency rate presented in the fall of 2011 was 74%, with a secondary patency rate of 92%. Angiographic core lab analysis demonstrated excessive device oversizing (> 20%) at the proximal edge in a number of cases. In devices that were oversized by < 20%, the primary patency was 91% on the proximal edge and 87% when oversized < 20% on the distal edge. Unlike previous studies in which the 5-mm device was associated with inferior patency rates, this was no longer the case in VIPER. Patency was again shown to be independent of lesion length (< 20 vs > 20 cm). The remarkable improvement in VIPER relative to VIBRANT occurred despite nearly identical mean lesion lengths, incidence of CTOs, vessel calcifications, and number of runoff vessels. As illustrated in Figure 3, longer lesion lengths (typical TASC II D lesions) are associated with substantial primary patency loss with BNS, but patency with the currentgeneration GORE® VIABAHN® Device is preserved and independent of lesion length.

Perhaps the most important lesson to be learned from the VIPER trial is the importance of proper vessel sizing, particularly to avoid oversizing the device by > 20%. Please see the Top 10 Technical Considerations in Using the GORE® VIABAHN® Device sidebar on page 4.

In a single-center study in Europe published by Lensvelt, similar efficacy results (primary patency, 76%) were reported using the latest-generation GORE® VIABAHN® Device in 18.5-cm lesions.52 The ongoing VIASTAR trial, a prospective, randomized, multicenter study, will evaluate the performance of the latest GORE® VIABAHN® Device relative to bare-metal stents in long lesions. Preliminary results have been presented, and patency results are in general agreement with those from the VIPER trial in long (approximately 20 cm) lesions.

CONCLUSION

Studies of BNS show a progressive loss of primary patency and a high incidence of stent fracture with increased lesion lengths. Covered stent grafts, in contradistinction, have good primary patency rates that are independent of lesion length and show great fracture resistance. The previous-generation stent graft was found to have equivalent patency to prosthetic femoropoliteal bypass for long SFA occlusive disease. In the VIPER trial, despite a mean lesion length of 19 cm, the new-generation GORE® VIABAHN® Device with proximal contoured edge and endoluminal heparin bonding was shown to provide excellent patency results, especially when devices were not oversized > 20% at the proximal edge. Stent grafts offer a less-invasive alternative to the greater morbidity associated with open bypass in patients with long TASC II D lesions. It is expected that future device improvements, such as treatment of the stent graft edges with paclitaxel, may further improve long-term patency rates.

Peter A. Soukas, MD, FACC, FSVM, FSCAI, is Director of Vascular Medicine and the Interventional PV Laboratory, Director of the Brown Vascular & Endovascular Medicine Fellowship at The Miriam and Rhode Island Hospitals, and Assistant Professor of Medicine at the Warren Alpert School of Medicine of Brown University in Providence, Rhode Island. He has disclosed that he is a consultant to W. L. Gore & Associates. Dr. Soukas may be reached at psoukas@lifespan.org.

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