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The Use of Femoropopliteal Stent-Grafts for Critical Limb Ischemia
The Use of Femoropopliteal Stent-Grafts for Critical Limb Ischemia Gary M. Ansel, MD, Charles F. Botti, Jr, MD, and Mitchel J. Silver, DO Peripheral vascular disease of the femoropopliteal segment is one of the most common anatomic locations leading to patient symptoms. Traditional open surgical bypass has started to be supplanted by a surge in lower risk endovascular procedures. Though midterm results of endovascular therapy have been acceptable, longer term results, especially in long diffuse disease, appear to be less durable than their surgical alternatives. Recently the Viabahn, a percutaneously placed PTFE stent-graft, has been approved for use in the femoropopliteal artery. Though the majority of the data for this stent-graft has been derived from patients with complex (>10 cm length) lesions, most of the patients have been claudicants. The population with critical limb ischemia is at particularly high risk for cardiovascular mortality and may benefit from this less invasive approach. However, stent-graft utilization is more complex and many variables must be evaluated before and during the procedure to allow for optimal procedural outcomes. Tech Vasc Interventional Rad 8:140-145 © 2005 Elsevier Inc. All rights reserved. KEYWORDS stent, arterial, stent-graft, femoropopliteal, angioplasty
D
isease of the femoropopliteal (FP) artery is one of the most common anatomic locations leading to patient symptoms. Claudication is the typical symptom when a single arterial level is involved. Critical limb ischemia (CLI) is more common when the femoral disease is part of a multilevel obstructive process. The FP arterial segment is unique in that it experiences a multitude of external forces including compression, elongation, and twisting. Atherosclerosis affecting the FP is commonly a diffuse process.1 However, due to varying levels of fibrosis and calcification, the FP segment is very heterogeneous among patients. Historically, patients with diffuse FP disease and limb-threatening ischemia have been treated with either prosthetic or venous surgical bypass.2 However, surgical morbidity and mortality have led to a surge in the use of percutaneous endovascular techniques, which by their nature are inherently lower risk. Controversy exists due to the paucity of reliable controlled and comparable data. The recently published BASIL trial has shown the clinical utility of a percutaneous approach for patients with CLI.3 Application of the various endovascular techniques in the appropriate patient population certainly may affect procedure durability. Variables that may affect outcome durabil-
MidOhio Cardiology and Vascular Consultants, Riverside Methodist Hospital, Columbus, Ohio. Address reprint requests to Gary M. Ansel, MD, MidOhio Cardiology and Vascular Consultants, Riverside Methodist Hospital, Columbus, OH. E-mail: [email protected].
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1089-2516/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2006.04.002
ity include lesion length, vessel diameter, diabetes, renal insufficiency, smoking, and quality of distal runoff.4,5
Endovascular Procedures PTA and Cryoplasty Closely examining previous controlled endovascular trials can assist in defining restenosis for balloon angioplasty. The Intracoil stent versus balloon trial allowed for lesion lengths up to 16 cm. However, investigators usually enrolled patients with focal disease leading to a short average lesion length of 3.3 cm. The 9-month angiographic restenosis (ⱖ50%) rate for the balloon control arm was 33.7%.6 The Peripheral Arteries Radiation Investigational Study trial compared stand-alone PTA to PTA with adjunctive brachytherapy. With an average lesion length of 5.8 cm, the 9-month angiographic restenosis rate for stand-alone PTA was 28%.7 Cejna and coworkers8 randomized patients to PTA or Palmaz stenting for lesions less than 5 cm. The 1-year angiographic restenosis rate for the balloon arm was 47%. For more diffuse SFA disease the results of balloon angioplasty have been best characterized by the Vienna-3 (brachytherapy) and Peripheral Excimer Laser Angioplasty (PELA) trials. The Vienna-3 trial, with a mean lesion length of 10.3 cm, showed 12-month angiographic restenosis rate for stand-alone PTA to be 64%.9 The PELA trial with the longest and most complex lesion lengths (20-cm occlusions) demonstrated a 9-month restenosis rate for PTA of 85%.10 Recently, registry data evaluating cryoplasty has been published. This registry of similarly short lesions (4.7 cm) showed the 9-month, duplex-controlled restenosis rate to be 30%.11
Femoropopliteal stent-grafts for critical limb ischemia
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Laser and Directional Atherectomy Atherectomy and excimer laser have been shown to be excellent tools for debulking; unfortunately, neither have shown any improved patency over balloon angioplasty.12-14
Bare Metal Stents Bare metal stents have been utilized in an effort to decrease clinically significant restenosis by increasing the postprocedural vessel luminal diameter. Early stainless steel stents did not show much clinical utility for a multitude of reasons including poor study design.15,16 More promising results have been reported for nitinol stents.17,18 However, not all nitinol stents appear to act the same after placement. Some nitinol stents experience a clinically relevant higher rate and complexity of stent fracture. Recent European data certainly suggest that some nitinol stents such as the Smart Stent (Cordis Endovascular, Warren, NJ) may develop less clinically significant fractures. There may, however, be a problem utilizing other nitinol stents such as the Luminexx (Bard Inc., Boston, MA) and Self-X (Abbott Vascular, Redwood City, CA) stents in the FP vascular bed. These two stents appear to be prone to complex fractures that result in decreased patency.19,20 Overall though, nitinol stents have shown good clinical utility and acceptable restenosis rates at short- and mid-term follow-up. Limited retrospective data for longer lesions appear to show an approximately 40% restenosis rate at 2 years.21 The addition of sirolimus to the self-expanding Smart Stent has not demonstrated significant benefit, possibly due to problematic drug elution rates.22
Covered Stents Covered stents were originally utilized for exclusion of arterial aneurysm. However, interest in covered stents for atherosclerotic disease has emerged in an effort to improve longer term restenosis rates. The potential uses for a covered stent include the treatment of aneurysms, de novo atherosclerotic lesions, in-stent restenosis, treatment of a failing surgical bypass, and percutaneous extravascular arterial bypass. Early covered stents included devices such as the Cragg system (Min Tec, Freeport, Bahamas) and Wallgraft (Boston Scientific Corp., Boston, MA) for the treatment of atherosclerotic disease. Clinical efficacy in the FP was suboptimal with low patency and significant thrombosis rates.23,24 The early covering materials such as Dacron seem to elicit a significant inflammatory response with associated poor patency rate and high thrombosis rates.25 Subsequently, most industry attention has been directed to the use of stents covered with polytetrafluoroethylene (PTFE). The use of PTFE in surgical bypass is well documented and this material has shown favorable tissue interaction. Complete neointima formation has been documented, though for long segment disease, this process may take many months.26 Up until recently there were three PTFE-covered stents commercially available in the United States: the biliary approved Fluency (C.R. Bard Inc., Covington, GA); the recently femorally approved Viabahn (W.L. Gore and Associates Inc., Flagstaff, AZ) (Figs. 1 and 2); and the recently discontinued spiral configured Aspire (Vascular Architects Inc., San Jose, CA).
Figure 1 Picture of the Viabahn stent-graft. (Color version of figure is available online.)
An international feasibility trial of the earlier version of the current Viabahn named the Hemobahn (W.L. Gore and Associates Inc.) was associated with very high technical success and a 79% primary patency at 1 year.27 Though no large multicenter randomized trial results have been published evaluating for the current Viabahn stent-graft, there are several published registries that have reported 1- and 2-year patencies of approximately 82 and 77%, respectively.28-30 Though the majority of patients in these studies were claudicants, the lesions were complex with average lesion lengths of over 10 cm. In contrast there are four studies that have shown poor results with 1-year patencies of under 70%; however, these studies have many procedural shortcomings including the inability to cover the entire angioplasty zone; ballooning outside the area of stent deployment; suboptimal antiplatelet therapy; and limited balloon dilation post stent deployment.31-33 In a multicenter study by Fischer and coworkers, poor results were noted when deviating from the protocol, which excluded heavily calcified lesion and patients with less than one vessel tibial runoff. If these patients are removed, the overall results come more into line with the more favorable reports.34 Though these findings appear to compare very favorably with prosthetic femoropopliteal bypass, one must recall that surgical series typically enter patients with a preponderance of CLI. There are published series that have evaluated the Viabahn PTFE-covered stent in patient populations with primarily CLI. Railo and coworkers in a small series of 15 patients (73% CLI) and relatively short lesions (4 to 10 cm) reported a primary patency at 1 and 2 years of 93 and 84%, respectively.35 Bauermeister and coworkers evaluated the use of the Viabahn in 35 patients with more diffuse disease, a mean lesion length of 22 cm (74% with CLI). In this series in which 40% also underwent common femoral surgical patching and 20% ring-stripper disobliteration showed a 1-year primary patency of 73% by duplex scanning.36 In the only randomized trial of claudicants versus CLI treated with the Hemobahn, Hartung and coworkers reported similar 1-year primary patencies of 81.3 and 88.9%, respectively. The average lesion lengths were similar at 9.8 and 11.7 cm, respectively. However, the tibial outflow status at baseline was sig-
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Figure 2 (A) Preprocedure angiography demonstrating occlusion of the superficial femoral artery. (B) Angiography after stent-graft placement.
nificantly different with 0 to 1 tibial vessels in 18.7% of the claudicants and 88.9% of the CLI group. Outflow procedures, which consisted of primarily balloon angioplasty, were completed in 6.3% of the claudicants and 66.7% of the CLI group.37
Mode of Failure The etiology of endovascular stent-graft or Viabahn failure is related to the amount of time that has lapsed since the procedure. Early procedural failure usually presents as stentgraft thrombosis. As for any vascular procedure, early failure is usually due to technical failure. Technical failure may be related to lack of periprocedural anticoagulation, hypercoagulable state. Not uncommonly a period of hypoperfusion or hypotension may occur during sheath removal and may be causative. Technical failure of stent-grafts would primarily include incomplete arterial stent-graft dilation, excessive stent-graft oversizing leading to material redundancy, and unrecognized proximal or distal dissection. These failures can be minimized by appropriate graft sizing (1:1 ratio), care-
ful postdilation taking care not to dilate beyond the grafted zone, and pressure gradient measurement to assess adequacy of stent-graft deployment. An intermediate time for procedural failure (6 to 24 months) is most commonly due to excessive intimal hyperplasia at the end of the stent-graft (Fig. 2). Late stent-graft failure is commonly secondary to progression of proximal or distal vascular occlusive disease.
Technical Considerations Since atherosclerosis is a diffuse progressive disease process, surgeons have shown that adequate inflow to the proximal graft is important. Even minor disease proximal to a bypass graft has been correlated with a decrease in long-term graft patency due to disease progression.38 It certainly appears important to place any stent-graft only after ensuring that proximal iliac or femoral disease has been adequately treated. With these considerations in mind, it would also appear optimal to begin and end the stent-graft in as normal an artery as possible.
Femoropopliteal stent-grafts for critical limb ischemia
Figure 3 Angiogram demonstrating edge restenosis (white arrow) at the proximal end of a previously placed stent-graft.
Status of distal runoff vessels has been shown to affect the durability of both surgical bypass and endovascular procedures. Tibial vessel runoff patency has been shown to also be a predictor of patency for endovascular procedures. Intervention with two- to three-vessel distal runoff is associated with significant improvement in patency compared with patients with 0 to 1 vessel runoff.39,40 Tibial patency may explain why both surgical and endovascular procedures appear to be more durable in claudicants than patients with critical limb ischemia. Anatomic position is an important consideration. Prosthetic surgical grafts that cross the knee joint are associated with inferior results with 4-year primary patency rates of approximately 40%.41 Though not currently studied in the occlusive disease population, studies evaluating covered stent-grafting of popliteal aneurysms have seen stent-graft occlusion to occur in 20 to 22% (1 year).42,43 The current Viabahn device is not approved for use in the popliteal artery and risk-benefit would need to be clear before off-label use. One must weigh the risk-benefit of crossing a diseased but potential collateral source to end the stent-graft in a less diseased, more distal vessel. Final lumen diameter should be maximized (Fig. 3). Significant calcification has been associated with lower longterm patency after balloon angioplasty. Severe vessel calcification may not allow for full stent-graft deployment and result in a much smaller final lumen diameter and possibly in-folding of the stent-graft. It would appear to make scientific sense to optimize the stent-graft deployment diameter and to size the Viabahn to the true vessel size by aggressive post-stent-graft balloon dilation. Utilizing intravascular ultrasound (IVUS) early in one’s experience may help to evaluate the necessity of an optimal angiographic result. The use of shorter balloon lengths and high inflation pressures may improve stent-graft deployment especially in fibrotic or cal-
143 cified vessels. Whether debulking of lesions before stent-graft placement will lead to more optimal final luminal diameter and the possible affect on patency is currently unknown. Special attention to antiplatelet therapy may be beneficial. Acetylsalicylic acid (ASA) can be recommended based on its ability to reduce thrombotic events in vascular patients. Clopidogrel has been noted to decrease cardiac and cerebrovascular events in patients with both coronary and peripheral vascular disease.44 ASA has been shown to reduce thrombotic closure of above knee prosthetic grafting.45 Similar improved patency has been seen with ticlopidine in a randomized multicenter trial.46 There is theoretical benefit in regards to dual antiplatelet therapy in perhaps obtaining longer term patency with covered stents. Direct stenting without predilation, especially of total occlusions, is not recommended for stent-graft deployment since it may be difficult or impossible to advance the bulkier stent-graft devices and does not allow for testing the native vessel’s ability to undergo successful dilation. Stent overlap may need to be increased. With bare metal stents excessive overlap may lead to increased rigidity and some feel increase the likelihood for potential stent fracture. Because of the independent stent elements that make up the currently approved Viabahn, it is very flexible and overlapping should lead to less compromise other than redundant graft material. The overlap should take into consideration the potential for vessel movement and increased overlap up to 1 to 1.5 cm may be appropriate. Physician operators must weigh the potential for the patient’s clinical benefit with the risk of collateral coverage as they treat their patients with stent-grafts. While potentially offering reduced restenosis, the use of a stent-graft also leads to covering potential collateral vessels. Bare metal stents are often able to preserve collateral vessels. Certainly the covering of collateral vessels becomes more of an issue as one treats more distally in the popliteal segment. However, preservation of collaterals should not take precedence over completely covering significant atherosclerotic disease. Thigh discomfort has been reported in approximately 6 to 20% of patients undergoing placement of stent-grafts in the SFA.27,29,35 It is felt that this may represent an inflammatory response. However, many centers are very aggressive in postdilation and this may represent procedural trauma. The symptoms may last up to 1 to 2 weeks and be accompanied by low-grade fever. These clinical symptoms usually respond to conservative care and antiinflammatory or analgesic medications.
Stent-Graft Surveillance Interestingly, most of the loss of patency for stent-grafts appears to occur in the first 12 months. Surveillance programs have shown convincing evidence of benefit for the detection of vein graft stenoses predictive of progression to occlusion.47 However, duplex imaging has not consistently been shown be effective for the detection of failing prosthetic grafts.48,49 There are no data on surveillance programs for femoral stentgrafts like the Viabahn. Restenosis at the distal ends of the stent-grafts can be detected by duplex scanning and appear to be associated with eventual thrombosis. It certainly appears appropriate to see the patient that has been treated with a
G.M. Ansel, C.F. Botti, and M.J. Silver
144 stent-graft back at regular intervals for evaluation with anklebrachial index and color-flow duplex scanning.
18.
Summary The early reports evaluating stent-graft use in the FP segment appear encouraging. However, the use of these devices is more complex and detailed planning must be completed to allow for optimization that should transfer to improved durability. Issues including extent of popliteal coverage, collateral coverage, appropriate type and duration of antiplatelet therapy, concomitant tibial intervention, and surveillance need more complete understanding and investigation. Current reports suggest stent-grafts may offer a safe and efficacious therapeutic option for carefully selected patients with claudication or critical limb ischemia.
References 1. Adar R, Critchfield GC, Eddy DM: A confidence profile analysis of the results of fempop percutaneous transluminal angioplasty in the treatment of lower extremity ischemia. J Vasc Surg 10:57-67, 1989 2. Hunink MG, Wong JB, Donaldson MC, et al: Patency results of percutaneous and surgical revascularizations for femoropopliteal arterial disease. Med Decis Making 14:71-81, 1994 3. Adam DJ, Beard JD, Cleveland T, et al: BASIL trial participants. Bypass versus angioplasty in severe ischemia of the leg (BASIL): multicenter, randomized controlled trial Lancet 366:1925-1934, 2005 4. Johnson KW: Femoral and popliteal arteries: reanalysis of results of balloon angioplasty. Radiology 183:767-771, 1992 5. Gray BH, Olin JW: Limitations of percutaneous angioplasty and stenting for femoropopliteal arterial occlusive disease. Semin Vasc Surg 10: 8-16, 1997 6. FDA Intracoil data. Food and Drug Administration. Cardiovascular and Radiologic Health Advisory Board. 2001;April 23 7. Waksman R. Paris. brachytherapy IR192 offers no benefit. http://www. tctmd.comm/csportal/appmanager/tctmd/main?_nfpb⫽true&_ pageLabel⫽TCTMDContent&hdCon⫽92079 8. Cejna M, Thurnher S, Illiasch H, et al: PTA versus Palmaz stent placement in femoropopliteal artery obstructions: a multicenter prospective randomized study. J Vasc Interv Radiol 12:23-31, 2001 9. Pokrajac B, Potter R, Roswitha M, et al: Endovascular brachytherapy prevents restenosis after femoropopliteal angioplasty: results of the Vienna-3 randomized multicenter trial. Radiother Oncol 74:3-9, 2005 10. Laird J. Laser applications in the periphery. http://tctmc.com/csportal/ appmanager/tctmd/main?_nfpb⫽true&pageLabel⫽TCTMDContent &hdCon⫽836311 11. Laird J, Jaff MR, Biamino G, et al: Cryoplasty for the treatment of femoropopliteal arterial disease: results of a prospective, multicenter registry. J Vasc Interv Radiol 16:1067-1073, 2005 12. Scheinert D, Laird J, Schroeder M, et al: Excimer laser-assisted recanalization of long, chronic superficial femoral artery occlusions. J Endovasc Ther 8:156-166, 2001 13. Tielbeek AV, Vroegindeweij D, Buth J, et al: Comparison of balloon angioplasty and Simpson atherectomy for lesions in the femoropopliteal artery: angiographic and clinical results of a prospective randomized trial. J Vasc Interv Radiol 7:837-844, 1996 14. Zeller T, Rastan A, Schwarzwalder U, et al: Percutaneous peripheral atherectomy of femoropopliteal stenoses using a new-generation device: six-month results from a single-center experience. J Endovasc Ther 11:676-685, 2004 15. Martin EC, Katzen BT, Benenati JF, et al: Multicenter trial of the wallstent in the iliac and femoral arteries. J Vasc Interv Radiol 6:843-849, 1995 16. Gray BH, Sullivan TM, Childs MB, et al: High incidence of restenosis/ reocclusion of stents in the percutaneous treatment of long-segment superficial femoral artery disease after suboptimal angioplasty. J Vasc Surg 25:74-83, 1997 17. Sabeti S, Schillinger M, Amighi J, et al. Primary patency of femoropopliteal arteries treated with nitinol versus stainless steel self-expanding
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stents: propensity score-adjusted analysis Radiology 232:516-521, 2004 Ansel GM, Silver MJ, Botti CF Jr, et al. Functional and clinical outcomes of nitinol stenting with and without abciximab for complex superficial femoral artery disease: a randomized trial. Catheter Cardiovasc Interv 2006 (in press) Scheinert D. Nitinol stent fractures in different nitinol self-expanding stents. a prospective evaluation. http://www.tctmd.com/csportal/ appmanager/tctmd/main?_nfpb⫽true&_pageLabel⫽TCTMDContent &hdCon⫽808868 Scheinert D, Scheinert S, Sax J, et al: Prevalence and clinical impact of stent fractures after femoropopliteal stenting. Am Coll Cardiol 45:312315, 2005 Mewissen MW: Self-expanding nitinol stents in the femoropopliteal segment: technique and mid-term results. Tech Vasc Interv Radiol 7:2-5, 2004 Duda SH, Pusich B, Richter G, et al: Sirolimus-eluting stents for the treatment of obstructive superficial femoral artery disease: six-month results. Circulation 106:1505-1509, 2002 Cragg AH, Dake MD: Treatment of peripheral vascular disease with stent-grafts. Radiology 205:307-314, 1997 Henry M, Amor M, Cragg A, et al: Occlusive and aneurysmal peripheral arterial disease: assessment of a stent-graft system. Radiology 201:717724, 1996 Ahmadi R, Schillinger M, Maca T, et al: Femoropopliteal arteries: immediate and long-term results with a Dacron-covered stent-graft. Radiology 223:345-350, 2002 Marin J, Veith F, Cynamon J, et al: Human transluminal placed endovascular stented grafts: preliminary histopathologic analysis of healing grafts in aortoiliac and femoral artery occlusive disease. J Vasc Surg 21:595-604, 1995 Lammer J, Dake MD, Bleyn J, et al: Peripheral arterial obstruction: prospective study of treatment with a transluminally placed self-expanding stent-graft. International Trial Study Group. Radiology 217(1):95-104, Jahnke T, Andresen R, Muller-Hulsbeck S, et al: Hemobahn stent-grafts for treatment of femoropopliteal arterial obstructions: midterm results of a prospective trial. J Vasc Interv Radiol 14(1):41-51, Saxon RR, Coffman JM, Gooding JM, et al: Stent-graft use in the femoral and popliteal arteries. Tech Intervent Vasc Radiol 7:6-15, 2004 Turicchia GU, Cevolani M, Altini R, et al: Mid-term results in PTFE endograft treatment of femoropopliteal occlusive disease. Osp Ital Chir 9:93-96, 2003 Deutschmann HA, Schedlbauer P, Berczi V, et al: Placement of Hemobahn stent-grafts in femoropopliteal arteries: early experience and midterm results in 18 patients. J Vasc Interv Radiol 12(8):943-950, Bray PJ, Robson WJ, Bray AE: Percutaneous treatment of long superficial femoral artery occlusive disease: efficacy of the Hemobahn stentgraft. J Endovasc Ther 10(3):619-628, Daenens K, Maleux G, Fourneau I, et al: Hemobahn stent-grafts in the treatment of femoropopliteal occlusive disease. J Cardiovasc Surg 46: 25-29, 2005 Fischer M, Langhoff R, Schulte KL: Hemobahn-endoprosthesis: long term experience (⬍ or ⫽ 4 years follow up) with percutaneous application in stenoses and occlusions of the superficial femoral artery. Zentralbl Chir 128:740-745, 2003 Railo M, Roth WD, Edgren J, et al: Preliminary results with endoluminal femoropopliteal thrupass. Ann Chir Gynaecol 90(1):15-18, Bauermeister G: Endovascular stent-grafting in the treatment of superficial femoral artery occlusive disease. J Endovasc Ther 8(3):315-320, Hartung O, Otero M, Dubuc M, et al: Efficacy of hemobahn in the treatment of superficial femoral artery lesions in patients with acute or critical ischemia: a comparative study with claudicants. Eur J Vasc Endovasc Surg 30:300-306, 2005 Rosenbloom MS, Walsh JJ, Schuler JJ, et al: Long-term results of infragenicular bypasses with autologous vein originating from the distal superficial femoral and popliteal arteries. J Vasc Surg 7:691-696, 1988 Gallino A, Mahler F, Probst P, et al: Percutaneous transluminal angioplasty of the arteries of the lower limbs: a 5 year follow-up. Circulation 70:619-623, 1984 Jeans WD, Armstrong S, Cole SEA, et al. Fate of patients undergoing transluminal angioplasty for lower-limb ischemia 177:559-564, 1990
Femoropopliteal stent-grafts for critical limb ischemia 41. Schweiger H, Klein P, Lang W: Tibial bypass grafting for limb salvage with ringed polytetrafluoroethylene prostheses: results of primary and secondary procedures. J Vasc Surg 18:867-874, 1993 42. Tielliu IF, Verhoeven EL, Prins TR, et al: Treatment of popliteal artery aneurysms with the Hemobahn stent-graft. J Endovasc Ther 10:111116, 2003 43. Tielliu IF, Verhoeven EL, Zeebregts CJ, et al: Endovascular treatment of popliteal artery aneurysms: results of a prospective cohort study. J Vasc Surg 41:561-567, 2005 44. CAPRIE steering committee: A randomized, blinded trial of clopidogrel versus aspirin in patients at risk of ischaemic events (CAPRIE). Lancet 348:1329-1339, 1996 45. Green RM, Roedersheimer LR, DeWeese JA: Effects of aspirin and di-
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pyridamole on expanded polytetrafluoroethylene graft patency. Surgery 92:1016-1026, 1982 Becquemin JP, Effect of ticlopidine on the long term patency of saphenous vein bypass grafts in the legs. N Engl J Med 337:17261731, 1997 Cohen JR, Mannick JA, Couch NP, et al: Recognition and management of impending graft failure: importance for long-term patency. Arch Surg 121:758-759, 1986 Lalak NJ, Hanel KC, Hunt J, et al: Duplex-scan surveillance of infrainguinal prosthetic grafts. J Vasc Surg 20:637-641, 1994 Dunlop P, Sayers RD, Naylor AR, et al: The effect of a surveillance program on the patency of prosthetic infrainguinal bypass grafts. Eur J Vasc Endovas Surg 11:441-445, 1996
D
isease of the femoropopliteal (FP) artery is one of the most common anatomic locations leading to patient symptoms. Claudication is the typical symptom when a single arterial level is involved. Critical limb ischemia (CLI) is more common when the femoral disease is part of a multilevel obstructive process. The FP arterial segment is unique in that it experiences a multitude of external forces including compression, elongation, and twisting. Atherosclerosis affecting the FP is commonly a diffuse process.1 However, due to varying levels of fibrosis and calcification, the FP segment is very heterogeneous among patients. Historically, patients with diffuse FP disease and limb-threatening ischemia have been treated with either prosthetic or venous surgical bypass.2 However, surgical morbidity and mortality have led to a surge in the use of percutaneous endovascular techniques, which by their nature are inherently lower risk. Controversy exists due to the paucity of reliable controlled and comparable data. The recently published BASIL trial has shown the clinical utility of a percutaneous approach for patients with CLI.3 Application of the various endovascular techniques in the appropriate patient population certainly may affect procedure durability. Variables that may affect outcome durabil-
MidOhio Cardiology and Vascular Consultants, Riverside Methodist Hospital, Columbus, Ohio. Address reprint requests to Gary M. Ansel, MD, MidOhio Cardiology and Vascular Consultants, Riverside Methodist Hospital, Columbus, OH. E-mail: [email protected].
140
1089-2516/05/$-see front matter © 2005 Elsevier Inc. All rights reserved. doi:10.1053/j.tvir.2006.04.002
ity include lesion length, vessel diameter, diabetes, renal insufficiency, smoking, and quality of distal runoff.4,5
Endovascular Procedures PTA and Cryoplasty Closely examining previous controlled endovascular trials can assist in defining restenosis for balloon angioplasty. The Intracoil stent versus balloon trial allowed for lesion lengths up to 16 cm. However, investigators usually enrolled patients with focal disease leading to a short average lesion length of 3.3 cm. The 9-month angiographic restenosis (ⱖ50%) rate for the balloon control arm was 33.7%.6 The Peripheral Arteries Radiation Investigational Study trial compared stand-alone PTA to PTA with adjunctive brachytherapy. With an average lesion length of 5.8 cm, the 9-month angiographic restenosis rate for stand-alone PTA was 28%.7 Cejna and coworkers8 randomized patients to PTA or Palmaz stenting for lesions less than 5 cm. The 1-year angiographic restenosis rate for the balloon arm was 47%. For more diffuse SFA disease the results of balloon angioplasty have been best characterized by the Vienna-3 (brachytherapy) and Peripheral Excimer Laser Angioplasty (PELA) trials. The Vienna-3 trial, with a mean lesion length of 10.3 cm, showed 12-month angiographic restenosis rate for stand-alone PTA to be 64%.9 The PELA trial with the longest and most complex lesion lengths (20-cm occlusions) demonstrated a 9-month restenosis rate for PTA of 85%.10 Recently, registry data evaluating cryoplasty has been published. This registry of similarly short lesions (4.7 cm) showed the 9-month, duplex-controlled restenosis rate to be 30%.11
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141
Laser and Directional Atherectomy Atherectomy and excimer laser have been shown to be excellent tools for debulking; unfortunately, neither have shown any improved patency over balloon angioplasty.12-14
Bare Metal Stents Bare metal stents have been utilized in an effort to decrease clinically significant restenosis by increasing the postprocedural vessel luminal diameter. Early stainless steel stents did not show much clinical utility for a multitude of reasons including poor study design.15,16 More promising results have been reported for nitinol stents.17,18 However, not all nitinol stents appear to act the same after placement. Some nitinol stents experience a clinically relevant higher rate and complexity of stent fracture. Recent European data certainly suggest that some nitinol stents such as the Smart Stent (Cordis Endovascular, Warren, NJ) may develop less clinically significant fractures. There may, however, be a problem utilizing other nitinol stents such as the Luminexx (Bard Inc., Boston, MA) and Self-X (Abbott Vascular, Redwood City, CA) stents in the FP vascular bed. These two stents appear to be prone to complex fractures that result in decreased patency.19,20 Overall though, nitinol stents have shown good clinical utility and acceptable restenosis rates at short- and mid-term follow-up. Limited retrospective data for longer lesions appear to show an approximately 40% restenosis rate at 2 years.21 The addition of sirolimus to the self-expanding Smart Stent has not demonstrated significant benefit, possibly due to problematic drug elution rates.22
Covered Stents Covered stents were originally utilized for exclusion of arterial aneurysm. However, interest in covered stents for atherosclerotic disease has emerged in an effort to improve longer term restenosis rates. The potential uses for a covered stent include the treatment of aneurysms, de novo atherosclerotic lesions, in-stent restenosis, treatment of a failing surgical bypass, and percutaneous extravascular arterial bypass. Early covered stents included devices such as the Cragg system (Min Tec, Freeport, Bahamas) and Wallgraft (Boston Scientific Corp., Boston, MA) for the treatment of atherosclerotic disease. Clinical efficacy in the FP was suboptimal with low patency and significant thrombosis rates.23,24 The early covering materials such as Dacron seem to elicit a significant inflammatory response with associated poor patency rate and high thrombosis rates.25 Subsequently, most industry attention has been directed to the use of stents covered with polytetrafluoroethylene (PTFE). The use of PTFE in surgical bypass is well documented and this material has shown favorable tissue interaction. Complete neointima formation has been documented, though for long segment disease, this process may take many months.26 Up until recently there were three PTFE-covered stents commercially available in the United States: the biliary approved Fluency (C.R. Bard Inc., Covington, GA); the recently femorally approved Viabahn (W.L. Gore and Associates Inc., Flagstaff, AZ) (Figs. 1 and 2); and the recently discontinued spiral configured Aspire (Vascular Architects Inc., San Jose, CA).
Figure 1 Picture of the Viabahn stent-graft. (Color version of figure is available online.)
An international feasibility trial of the earlier version of the current Viabahn named the Hemobahn (W.L. Gore and Associates Inc.) was associated with very high technical success and a 79% primary patency at 1 year.27 Though no large multicenter randomized trial results have been published evaluating for the current Viabahn stent-graft, there are several published registries that have reported 1- and 2-year patencies of approximately 82 and 77%, respectively.28-30 Though the majority of patients in these studies were claudicants, the lesions were complex with average lesion lengths of over 10 cm. In contrast there are four studies that have shown poor results with 1-year patencies of under 70%; however, these studies have many procedural shortcomings including the inability to cover the entire angioplasty zone; ballooning outside the area of stent deployment; suboptimal antiplatelet therapy; and limited balloon dilation post stent deployment.31-33 In a multicenter study by Fischer and coworkers, poor results were noted when deviating from the protocol, which excluded heavily calcified lesion and patients with less than one vessel tibial runoff. If these patients are removed, the overall results come more into line with the more favorable reports.34 Though these findings appear to compare very favorably with prosthetic femoropopliteal bypass, one must recall that surgical series typically enter patients with a preponderance of CLI. There are published series that have evaluated the Viabahn PTFE-covered stent in patient populations with primarily CLI. Railo and coworkers in a small series of 15 patients (73% CLI) and relatively short lesions (4 to 10 cm) reported a primary patency at 1 and 2 years of 93 and 84%, respectively.35 Bauermeister and coworkers evaluated the use of the Viabahn in 35 patients with more diffuse disease, a mean lesion length of 22 cm (74% with CLI). In this series in which 40% also underwent common femoral surgical patching and 20% ring-stripper disobliteration showed a 1-year primary patency of 73% by duplex scanning.36 In the only randomized trial of claudicants versus CLI treated with the Hemobahn, Hartung and coworkers reported similar 1-year primary patencies of 81.3 and 88.9%, respectively. The average lesion lengths were similar at 9.8 and 11.7 cm, respectively. However, the tibial outflow status at baseline was sig-
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Figure 2 (A) Preprocedure angiography demonstrating occlusion of the superficial femoral artery. (B) Angiography after stent-graft placement.
nificantly different with 0 to 1 tibial vessels in 18.7% of the claudicants and 88.9% of the CLI group. Outflow procedures, which consisted of primarily balloon angioplasty, were completed in 6.3% of the claudicants and 66.7% of the CLI group.37
Mode of Failure The etiology of endovascular stent-graft or Viabahn failure is related to the amount of time that has lapsed since the procedure. Early procedural failure usually presents as stentgraft thrombosis. As for any vascular procedure, early failure is usually due to technical failure. Technical failure may be related to lack of periprocedural anticoagulation, hypercoagulable state. Not uncommonly a period of hypoperfusion or hypotension may occur during sheath removal and may be causative. Technical failure of stent-grafts would primarily include incomplete arterial stent-graft dilation, excessive stent-graft oversizing leading to material redundancy, and unrecognized proximal or distal dissection. These failures can be minimized by appropriate graft sizing (1:1 ratio), care-
ful postdilation taking care not to dilate beyond the grafted zone, and pressure gradient measurement to assess adequacy of stent-graft deployment. An intermediate time for procedural failure (6 to 24 months) is most commonly due to excessive intimal hyperplasia at the end of the stent-graft (Fig. 2). Late stent-graft failure is commonly secondary to progression of proximal or distal vascular occlusive disease.
Technical Considerations Since atherosclerosis is a diffuse progressive disease process, surgeons have shown that adequate inflow to the proximal graft is important. Even minor disease proximal to a bypass graft has been correlated with a decrease in long-term graft patency due to disease progression.38 It certainly appears important to place any stent-graft only after ensuring that proximal iliac or femoral disease has been adequately treated. With these considerations in mind, it would also appear optimal to begin and end the stent-graft in as normal an artery as possible.
Femoropopliteal stent-grafts for critical limb ischemia
Figure 3 Angiogram demonstrating edge restenosis (white arrow) at the proximal end of a previously placed stent-graft.
Status of distal runoff vessels has been shown to affect the durability of both surgical bypass and endovascular procedures. Tibial vessel runoff patency has been shown to also be a predictor of patency for endovascular procedures. Intervention with two- to three-vessel distal runoff is associated with significant improvement in patency compared with patients with 0 to 1 vessel runoff.39,40 Tibial patency may explain why both surgical and endovascular procedures appear to be more durable in claudicants than patients with critical limb ischemia. Anatomic position is an important consideration. Prosthetic surgical grafts that cross the knee joint are associated with inferior results with 4-year primary patency rates of approximately 40%.41 Though not currently studied in the occlusive disease population, studies evaluating covered stent-grafting of popliteal aneurysms have seen stent-graft occlusion to occur in 20 to 22% (1 year).42,43 The current Viabahn device is not approved for use in the popliteal artery and risk-benefit would need to be clear before off-label use. One must weigh the risk-benefit of crossing a diseased but potential collateral source to end the stent-graft in a less diseased, more distal vessel. Final lumen diameter should be maximized (Fig. 3). Significant calcification has been associated with lower longterm patency after balloon angioplasty. Severe vessel calcification may not allow for full stent-graft deployment and result in a much smaller final lumen diameter and possibly in-folding of the stent-graft. It would appear to make scientific sense to optimize the stent-graft deployment diameter and to size the Viabahn to the true vessel size by aggressive post-stent-graft balloon dilation. Utilizing intravascular ultrasound (IVUS) early in one’s experience may help to evaluate the necessity of an optimal angiographic result. The use of shorter balloon lengths and high inflation pressures may improve stent-graft deployment especially in fibrotic or cal-
143 cified vessels. Whether debulking of lesions before stent-graft placement will lead to more optimal final luminal diameter and the possible affect on patency is currently unknown. Special attention to antiplatelet therapy may be beneficial. Acetylsalicylic acid (ASA) can be recommended based on its ability to reduce thrombotic events in vascular patients. Clopidogrel has been noted to decrease cardiac and cerebrovascular events in patients with both coronary and peripheral vascular disease.44 ASA has been shown to reduce thrombotic closure of above knee prosthetic grafting.45 Similar improved patency has been seen with ticlopidine in a randomized multicenter trial.46 There is theoretical benefit in regards to dual antiplatelet therapy in perhaps obtaining longer term patency with covered stents. Direct stenting without predilation, especially of total occlusions, is not recommended for stent-graft deployment since it may be difficult or impossible to advance the bulkier stent-graft devices and does not allow for testing the native vessel’s ability to undergo successful dilation. Stent overlap may need to be increased. With bare metal stents excessive overlap may lead to increased rigidity and some feel increase the likelihood for potential stent fracture. Because of the independent stent elements that make up the currently approved Viabahn, it is very flexible and overlapping should lead to less compromise other than redundant graft material. The overlap should take into consideration the potential for vessel movement and increased overlap up to 1 to 1.5 cm may be appropriate. Physician operators must weigh the potential for the patient’s clinical benefit with the risk of collateral coverage as they treat their patients with stent-grafts. While potentially offering reduced restenosis, the use of a stent-graft also leads to covering potential collateral vessels. Bare metal stents are often able to preserve collateral vessels. Certainly the covering of collateral vessels becomes more of an issue as one treats more distally in the popliteal segment. However, preservation of collaterals should not take precedence over completely covering significant atherosclerotic disease. Thigh discomfort has been reported in approximately 6 to 20% of patients undergoing placement of stent-grafts in the SFA.27,29,35 It is felt that this may represent an inflammatory response. However, many centers are very aggressive in postdilation and this may represent procedural trauma. The symptoms may last up to 1 to 2 weeks and be accompanied by low-grade fever. These clinical symptoms usually respond to conservative care and antiinflammatory or analgesic medications.
Stent-Graft Surveillance Interestingly, most of the loss of patency for stent-grafts appears to occur in the first 12 months. Surveillance programs have shown convincing evidence of benefit for the detection of vein graft stenoses predictive of progression to occlusion.47 However, duplex imaging has not consistently been shown be effective for the detection of failing prosthetic grafts.48,49 There are no data on surveillance programs for femoral stentgrafts like the Viabahn. Restenosis at the distal ends of the stent-grafts can be detected by duplex scanning and appear to be associated with eventual thrombosis. It certainly appears appropriate to see the patient that has been treated with a
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144 stent-graft back at regular intervals for evaluation with anklebrachial index and color-flow duplex scanning.
18.
Summary The early reports evaluating stent-graft use in the FP segment appear encouraging. However, the use of these devices is more complex and detailed planning must be completed to allow for optimization that should transfer to improved durability. Issues including extent of popliteal coverage, collateral coverage, appropriate type and duration of antiplatelet therapy, concomitant tibial intervention, and surveillance need more complete understanding and investigation. Current reports suggest stent-grafts may offer a safe and efficacious therapeutic option for carefully selected patients with claudication or critical limb ischemia.
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