Superficial Femoral Artery Occlusion: Nitinol Stents Achieve Flow and Reduce the Need for Medications Better than Balloon Angiop

Key words:balloon angioplasty, SFA, stents Stents have proven superior to balloon angioplasty in the treatment of coronary atherosclerosis in terms of reduction of acute complications and restenosis.^1,2 However, in the treatment of superficial femoral artery (SFA) stenosis, multiple studies have shown equivalent patency between balloon angioplasty and stenting.^3,4 Most of these studies used stainless steel stents, with minimal radial force and flexibility. To date, there has been no study assessing the efficacy of next generation stents compared to balloon angioplasty in the treatment of SFA stenosis. These stents have been characterized by the use of an alloy combining nickel, titanium and nitinol. Advantages include improved radial strength with special shape-memory characteristic, as well as reduced foreshortening which allows more precise placement. These properties may lead to greater rates of patency and procedural success compared to traditional Palmaz stents or balloon angioplasty. The purpose of this study was to compare angioplasty versus stenting using nitinol slotted tube stents in consecutive patients undergoing chronically occluded SFA treatment at the Cleveland Clinic Foundation Peripheral Vascular Lab. Methods Study group. Using The Cleveland Clinic Foundation Peripheral database, we identified 40 consecutive patients who underwent successful recanalization and revascularization for chronic total SFA occlusion from June 1999 to June 2002. A retrospective analysis of prospectively collected data was performed to determine whether outcomes after balloon angioplasty were equivalent to stents. We evaluated the reduction in the pressure gradient across the lesion and the associated reduction in the use of adjunctive medical treatment (pentoxifylline, cilostazol) between the two strategies. Patients had pre- and post-procedure ankle brachial index (ABI) measurements and had clinical follow-up at 6 months. All patients received aspirin and heparin prior to intervention. Patients were assigned to either balloon angioplasty or stenting at the discretion of the treating physicians. All of the stented patients had suboptimal percutaneous transluminal angioplasty results. There was either significant residual stenosis or long dissection in the treated site. Patients were stented with the SMART™ nitinol slotted tube stent. All stented patients received the adenosine diphosphate receptor antagonist clopidogrel for at least 1 month. Statistical analysis. Baseline characteristics were summarized by the use of frequencies and percentages for categorical factors and means ± standard deviation for continuous factors. Study outcome. To assess improvement in outcome, post-procedure ABI was measured. Follow-up time was 6 months. Patients did not undergo repeat angiography. Technical success was defined as residual diameter stenosis 3–9 The conditions associated with favorable outcome following SFA interventions include noncalcified discrete stenosis 3–5 cm in length in a vessel with reference vessel diameter > 7 mm.10 The assessment of the existing literature is limited by the fact that several studies did not distinguish between severe SFA stenosis and occlusion and the endpoint differed between clinical versus lumen patency.^3,4 From a procedural perspective, previous studies used stents with high metal surface area, which has been associated with high restenosis rates. In addition, the frequent use of warfarin in the absence of antiplatelet therapy may have added to stent thrombosis and reocclusion. Finally, these balloon-expandable stents have a known tendency toward deformation following external compression, with the potential for restenosis and occlusion.¹¹ The stents investigated in lower extremity interventions included Wallstent, Palmaz and Strecker stents. The Wallstent is a self-expanding, flexible, multi-strand mesh stent made of mediloy that is limited by substantial foreshortening. Also, it has been associated with early thrombosis and late intimal hyperplasia.¹² The Palmaz stent is a balloon-expandable stent with a stainless-steel, slotted tube design. It has moderate radial strength and shortens minimally, but has a tendency for stent deformation.¹² The Strecker stent is a balloon-expandable, flexible stent made of knitted tantalum wire, which provides moderate radial strength with some foreshortening; it also has the disadvantage of stent deformation following compression.¹² New generation stents have less surface metal area and are made of nitinol. Nitinol provides shape memory, superior elasticity, crush recoverability, stability and lumen integrity. The nitinol slotted tube design also confers good radial strength with higher chronic outward force. In addition, with the use of thienopyridines and adequate anticoagulation, the risk of early thrombosis has been substantially reduced. Finally, the self-expanding stents have virtually eliminated the complications associated with stent deformation. Many of the newer studies report angiographic restenosis rates of 10–30% with stenting and a clinical patency rate of 80% at 2 years. There are differences between angiographic restenosis rates versus clinical or hemodynamically significant restenosis. Several studies have shown higher rates of clinical patency rates compared to angiographic rates.5 Since the majority of SFA treatments are for symptom relief, clinical patency may be an additional relevant parameter to assess efficacy. Studies should focus on clinical endpoint as well as lumen patency rates. Our study is the first to show hemodynamic and clinical superiority of nitinol slotted tube stents in chronically occluded SFA lesions. Although the stent group had greater pre-procedural translesion gradients, the patients continued to have high rates of clinical patency at 6 months compared to the angioplasty group. They had greater reduction in post-procedure translesion gradient and had less post-procedural requirement for adjunctive medical treatment. Study limitations. There are several limitations to our study. This was a single center, retrospective, non-randomized analysis of a small sample group. Our patients did not undergo duplex ultrasound and most of them did not undergo repeat angiography. Therefore, vessel patency rate could not be determined. Our follow-up period was only 6 months. Therefore, long-term patency, clinical and hemodynamic assessment could not be determined. We also did not measure exercise time, but assessed claudication by the surrogate marker of adjunctive medical therapy use. Conclusion In chronically occluded SFA stenosis, stenting resulted in a lower translesion pressure gradient and reduced the need for vasodilators. Nitinol slotted tube stents may offer a unique advantage to angioplasty alone in patients with complex SFA disease. A large, multicenter, randomized trial using long-term follow-up with clinical and lumen patency rates with duplex ultrasound is required to determine the true benefit of these new devices.

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