Nitinol stents in hemodialysis access.

MAINTAINING permanent vascular access remains the Achilles heel of hemodialysis. In the era of widespread use of percutaneous angioplasty and thrombectomy for salvaging failing and failed hemodialysis accesses, the consensus guidelines of the National Kidney Foundation Dialysis Outcomes Quality Initiative recommend relatively modest benchmarks: a 50% 6-month patency rate after angioplasty and a 40% 3-month patency rate after thrombectomy (1,2). Clearly, there is significant room for improvement. According to the United States Renal Data System, the use of stents in dialysis access has significantly increased from 1991 to 2001 (Figure). In 2001, approximately 9% of hemodialysis access angioplasty procedures were associated with stent placement (3). Stents provide mechanical support to a site of stenosis that cannot be reached with percutaneous transluminal angioplasty (PTA). If a stent placed in a vein or at a venous anastomosis would never incite intimal hyperplasia, migrate, shorten, or fracture, there would be no debate about the issue, and interventionalists would just place stents in every patient. However, since the earliest report of dialysis access stent placement 15 years ago (4), most literature has indicated that a stent confers no benefit over successful angioplasty in longterm patency of hemodialysis access sites. Moreover, surgical revision at a site of unsuccessful angioplasty may be hampered or precluded by the presence of a stent. Gray et al (5) treated 52 patients with venous stenoses with use of self-expanding stents. At 12 months, the primary patency rate was 20% and the assisted primary patency rate was 33%. Kovalik et al (6) placed self-expanding stents in 10 patients, five of whom had elastic lesions that recurred after angioplasty. The appearance of venous outflow stenosis symptoms recurred in eight of 10 patients within 1 year. Vorwerk et al (7) placed 92 self-expanding stents in 65 patients with grafts or fistulas and achieved a higher cumulative 12month patency rate of 86% through an additional 1.3 surgical and/or radiological interventions/patient. In a small prospective trial, Hoffer et al (8) randomized patients with recurrent stenosis at the venous anastomosis of dialysis grafts to receive angioplasty alone or with placement of a self-expanding stent. Primary patency rates at 2 and 6 months were 53% and 23% in the PTA-only group and 56% and 12% in the stent group. Patel et al (9) implanted stents in lesions at the venous anastomosis in 25 patients, and reported a 6-month patency rate of 27%. Better results were seen in patients with stents placed at the site of balloon-induced venous rupture in a study by Raynaud et al (10). At 12 months, a primary patency rate of 48% was seen among 37 stent-implanted accesses, including synthetic grafts and native fistulas. Poorer results were seen in our experience (11) with stents for balloon-induced ruptures, in which we found that primary patency rates decreased from 63% at 3 months to 17% at 12 months. Vesely et al (12) observed a 25% 12-month primary patency rate among 20 patients who underwent self-expanding stent placement of central venous stenoses. Haage et al (13) placed 57 stents in 50 hemodialysis patients with central venous stenosis and reported a 56% 12month primary patency rate. These and other similar results have tempered the indications for stent placement. At present, the Quality Improvement Guidelines of the Society of Interventional Radiology (14) recommend that stents be reserved for (i) peripheral lesions in which PTA has failed and surgical access is difficult, surgery is contraindicated, or there are limited remaining access sites; (ii) central vein lesions in which PTA has failed or that recur within 3 months after initially successful PTA; or (iii) rupture of an outflow vein after PTA (14). Similarly, the consensus guidelines of the National Kidney Foundation Dialysis Outcomes Quality Initiative (1,2) recommend that the use of From the Section of Vascular and Interventional Radiology, Department of Radiology, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, Pennsylvania 19104. Received May 12, 2004; revision requested May 13; revision received May 22; accepted May 26. Address correspondence to T.W.I.C.; E-mail: timothy.clark@uphs.upenn.edu