Outcome of infra-inguinal bypass grafts using vein conduit with less than 3 millimeters diameter in critical leg ischemia

From the Society for Vascular Surgery

Outcome of infra-inguinal bypass grafts using vein conduit with less than 3 millimeters diameter in critical leg ischemia Hani Slim, MD, MRCS, Alok Tiwari, MS, FRCS, Jens Carsten Ritter, MD, and Hisham Rashid, MSc, FRCS, London, United Kingdom Objective: The purpose of this study was to evaluate the difference in amputation-free survival and patency rates of infra-inguinal bypass grafts in patients with critical leg ischemia (CLI) with vein conduits with an internal diameter <3 mm compared to those with vein conduits with a diameter of >3 mm. Methods: Retrospective analysis of all consecutive patients with CLI undergoing infra-inguinal bypass. Preoperative duplex scan mapping and measurement of potential vein grafts were performed on all patients. Patients were recruited in a 1-year duplex scan graft surveillance program. Primary end points were amputation-free survival and patency rates at 1 year postoperatively. Kaplan-Meier and ␹2 test were used for statistical analysis. Results: Between January 2004 and April 2010, 157 consecutive patients with CLI underwent 171 bypasses using vein conduits (111 men, 46 women; median age, 75 years; range, 45-96 years). Ninety-three bypasses (54.4%) were performed for tissue loss, 44 (25.7%) for gangrene, and for rest pain. Of the 157 patients, 113 (72.0%) had diabetes mellitus, 40 (25.5%) had renal impairment, 131 (83.4%) had hypertension, and 64 (40.8%) had ischemic heart disease. Femoropopliteal bypass was performed in 38 cases (22.2%), whereas 133 (77.8%) of the bypasses were femoro-distal. Autogenous great saphenous vein (GSV) was used in all cases. All grafts were reversed. The diameter of 31 (18%) vein conduits measured <3 mm (range, 2-2.9 mm) on preoperative duplex scan. One hundred thirty-four grafts had at least 1-year follow-up. The primary, assisted primary, and secondary patency rates at 1 year for vein conduits <3 mm were 51.2%, 82.6%, and 82.6%, respectively, compared to 68.4%, 93.3%, and 95.2%, respectively, in the >3 mm group. This was only significant for the secondary patency (P ⴝ .0392). The amputation-free survival at 48 months was 70.8% for vein conduits <3 mm and 57.3 for vein conduits >3 mm. Conclusion: This series has shown that primary and assisted primary patency rates in small veins are not significantly different at 1 year but the secondary patency rates are better in the larger veins. Similarly, the amputation-free survival was also comparable. The authors would, therefore, advocate the use of small veins >2 mm in diameter in patients with CLI. Duplex scan surveillance followed by early salvage angioplasty for threatened grafts is needed to achieve good patency rates in both groups. ( J Vasc Surg 2011;53:421-5.)

Lower extremity surgical arterial revascularization has assumed a prominent role in the prevention of major amputations secondary to critical leg ischemia (CLI) in both diabetic and non-diabetic patients with diabetes and without diabetes. Vein grafts in infra-inguinal bypass have stood the test of time in terms of durability and patency with the great saphenous vein (GSV) and other autogenous veins showing superiority to prosthetic grafts.1-4 Well-known reasons for improved graft patency are use of good quality autogenous conduit, above knee bypasses, and reduction of risk factors such as smoking and use of antiplatelet drugs. In terms of conduit, leg veins are preferred because of longer length, use of same incision, and good long-term results. From the Department of Vascular Surgery, King’s College Hospital. Competition of interest: none. Presented as an oral poster at the Vascular Annual Meeting, Boston, Mass, June 2010. Reprint requests: Hisham Rashid, MSc, FRCS, Department of Vascular Surgery, King’s College Hospital, Denmark Hill, London SE5 9RS, United Kingdom (e-mail: [email protected]). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a competition of interest. 0741-5214/$36.00 Copyright © 2011 by the Society for Vascular Surgery. doi:10.1016/j.jvs.2010.09.014

For patients with CLI requiring lower limb bypass who do not have an adequate vein, the choice is between a prosthetic graft with its low patency and associated complications such as infection, or to use a smaller diameter vein. The minimal accepted internal diameter for such venous conduit remains controversial. Previous studies suggested that vein grafts ⬍3.5 mm in diameter had overall poor patency rates, particularly in the reversed vein conduit.5-7 In our unit, the policy has always been to use an autogenous vein even if it is not of adequate internal diameter as long as it is more than 2 mm. In this report, the authors present the results of using veins of less than 3 mm internal diameter in a tertiary referral center over a period of 6 years in the management of patients with CLI. METHODS In the period between January 2004 and April 2010, 171 infra-inguinal bypasses using a reversed autogenous venous conduit were performed on patients under a single vascular surgeon. All patients with CLI (Rutherford classification, category 4, 5, or 6) due to long occlusive femoro-popliteal disease and/or trifurcation disease (TASC types C and D classification for femoro-popliteal disease)3 and those with 421

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acute complicated popliteal artery (PA) aneurysmal disease were included. Patients’ demographics, details of the operation, and follow-up information were recorded and entered prospectively into a database (Microsoft Access and Excel, Redmond, Wash). All patients had a preoperative arterial duplex scan in combination with conventional or computed tomography angiogram to delineate the anatomy of the arterial system. Because a large proportion of these patients were diabetic and had renal failure, we did not routinely use the ankle brachial pressure index due to an artificially high reading in such a group of patients. The authors’ policy is to operate on patients depending on the clinical situation and presence of damped waveforms in the crural vessels. Preoperative duplex scan vein mapping was performed on all patients according to a standard protocol. Experienced vascular scientists performed all examinations at King’s College Hospital vascular laboratory with the patient in the sitting position. The B-mode, real-time (Philips, IU22; Philips Healthcare, Best, The Netherlands) ultrasonographic duplex scanner with a 3-9 MHz transducer (linear L9-3, Philips) was used. Potential vein grafts were mapped along their entire course and the internal diameter of the vein was measured at multiple sites. The vein measurements and scan images were stored on the Centricity Enterprise Medical data system (GE Healthcare Life Sciences, Buckinghamshire, United Kingdom) for future reference. The presence and location of thrombus, scarring, or varicosities were also recorded. The location of the vein and its major tributaries were indelibly marked with a continuous line on the skin immediately before surgery. Sections of the vein where it was found to be ⬍3 mm were marked with a dotted line. Both GSVs were mapped. However, if these veins were harvested or stripped previously, the lesser saphenous veins were mapped using a similar technique. The smallest vein conduit used was 2 mm. Patients undergoing arm vein bypass were excluded. Revascularization was performed with the patient under general anesthesia unless contraindicated. The vein was harvested and flushed with heparin saline solution (1000 IU/mL; Wockhardt, Wrexham, United Kingdom) diluted in 1 liter of normal saline, and reversed. Tunneling of the bypass graft was performed anatomically. Bypasses to the anterior tibial and dorsalis pedis arteries were tunneled laterally through the interosseous membrane, whereas bypasses to the peroneal artery were performed through a medial approach. The distal anastomosis was performed using 7/0 polypropylene if below the PA. An intra-operative continuous wave Doppler scan was used to assess the graft patency at the end of the procedure for quality control. Postoperative anticoagulation was maintained using a therapeutic dose of low molecular weight heparin adjusted according to the patients’ body weight in all distal bypasses and prophylactic dose in femoro-popliteal bypasses and maintained throughout the in-hospital period. Antiplatelet and statin therapy was initiated before surgery and maintained postoperatively in all patients.

Table I. Patients’ demography and risk factors in both groups ⱖ3 mm group (n ⫽ 126)

⬍3 mm group (n ⫽ 31)

Median age (range) 75 years (45-96) 75 years (51-88) Men 91 20 Diabetes mellitus 87 (69.0%) 26 (83.9%) Renal insufficiency 33 (26.2%) 7 (22.6%) Hypertension 102 (81.0%) 29 (93.5%) Ischemic heart disease 50 (39.7%) 14 (45.2%) Smokers 21 (16.7%) 4 (12.9%) Ex-smokers 70 (55.6%) 18 (58.1%)

P value .39 .09 .68 .09 .57 .78 .84

All patients were recruited into a 1-year duplex scan graft surveillance program. Graft follow-up scans were performed before hospital discharge and then every 3 months for a year. Scans were performed for the inflow artery, the entire vein conduit, both anastomoses, and the outflow artery. A threatened graft was diagnosed upon the finding of focal peak systolic flow velocity ⬎200 cm/s, velocity ratio exceeding 2.0 (50% stenosis), or global graft flow velocity uniformly ⬍45 cm/s. Patients with threatened grafts were offered urgent angiography, and if a significant stenosis was confirmed, immediate angioplasty was performed. If the stenotic lesion fails to respond to angioplasty or recur after successful angioplasty, then corrective surgery was undertaken. The internal diameter of all vein grafts in the ⬍3 mm group was measured at 6 months. The diameter was compared with the preoperative vein mapping measurement. Vein conduits with an internal diameter measuring ⬍3 mm along their entire length on the preoperative vein duplex scan were analyzed separately to those measuring ⱖ3 mm in diameter. The primary end points were amputation-free survival and primary, assisted primary, and secondary patency rates of the bypass leg. Only data from the first year of follow-up were analyzed. Kaplan-Meier life-table analysis and ␹2 test were used where appropriate. P values ⬍ .05 were considered significant. Statistical analysis was done with Prism software 5.0 (Graph Pad Software, La Jolla, Calif). RESULTS Between January 2004 and April 2010, 157 consecutive patients with CLI underwent 171 infra-inguinal bypasses. The demographic characteristics and risk factors, defined and graded according to the Society for Vascular Surgery/International Society for Cardiovascular Surgery recommended criteria,8 were similar in both groups and are summarized in Table I. All patients had CLI (Rutherford grades 4, 5, and 6). One hundred sixty-four bypasses (95.9%) were operated on for occlusive disease and 7 (4.1%) for a complicated PA aneurysm. Tissue loss was present in 93 cases (54.4%), gangrene in 44 (25.7%), and rest pain in 34 (19.9%). Autogenous GSV was used in all cases (except 1 case where the lesser saphenous vein was used).

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Table II. Site of proximal anastomosis in both groups Inflow artery External iliac Common femoral Deep femoral Superficial femoral Above knee popliteal Below knee popliteal Posterior tibial

ⱖ3 mm groupa (n ⫽ 140)

⬍3 mm groupa (n ⫽ 31)

1 (0.7%) 30 (21.4%) 2 (1.4%) 45 (32.1%) 14 (10.0%) 46 (32.9%) 2 (1.4%)

0 5 (16.1%) 1 (3.2%) 16 (51.6%) 2 (6.5%) 7 (22.6%) 0

a

There were no statistical differences between the groups.

Table III. Site of distal anastomosis in both groups Outflow artery Popliteal above knee Popliteal below knee Anterior tibial Tibio–peroneal trunk Posterior tibial Peroneal Dorsalis pedis Medial plantar

ⱖ3 mm groupa (n ⫽ 140)

⬍3 mm groupa (n ⫽ 31)

20 (14.3%) 9 (6.4%) 27 (19.3%) 8 (5.7%) 35 (25.0%) 13 (9.3%) 22 (15.7%) 6 (4.3%)

4 (12.9%) 5 (16.1%) 10 (32.3%) 0 4 (12.9%) 7 (22.6%) 0 1 (3.2%)

Fig 1. Primary patency rates in both groups.

a

There were no statistical differences between the groups.

Sixty-one of the 171 bypasses were found to have inflow disease and underwent successful preoperative inflow angioplasty. Target arteries were: 5 common iliac, 5 external iliac, 2 common femoral, 22 superficial femoral, 15 PA, and 12 combined superficial femoral and PA. Details of the inflow and outflow arteries in both groups are summarized in Tables II and III. There was no significant difference between the 2 groups in terms of inflow and outflow vessels. Thirty-one (18%) vein conduits measured ⬍3 mm in internal diameter and 140 (82%) had a vein conduit ⱖ3 mm. The smallest vein conduit used was 2 mm whereas the largest was 9 mm. In the ⬍3 mm group, the range of vein conduit was 2 to 2.9 mm (median, 2.5 mm). The total in-hospital mortality was 4 patients (2.3%). In the ⬍3 mm group, the in-hospital mortality was 1 patient (3.1%), compared to 3 patients (2.1%) in the ⱖ3 mm group. This was not significant. The total 1-year mortality was 12.3% (n ⫽ 21). One hundred thirty-four bypasses had at least 1-year follow-up. Of these bypasses, 25 grafts were in the ⬍3 mm group and 109 in the ⱖ3 mm group. Salvage angioplasty was performed in 40.6% of the ⬍3 mm group compared to 26.9% in the ⱖ3 mm group (P ⫽ .122). At 1-year, the ⱖ3 mm group’s primary, assisted-primary, and secondary patency rates were 68.4%, 93.3%, and 95.2%, respectively. This compares to patency rates of 51.2%, 82.6%, and 82.6%, respectively, in the ⬍3 mm group (Figs 1, 2, and 3). This was only significant for the secondary patency (P ⫽ .0392). Amputation-free survival at 12, 36, and 48 months was similar in both groups (84.1%, 63.0%, and 57.3%,

Fig 2. Assisted primary patency rates in both groups.

respectively, in the ⱖ3 mm group compared to 86.0%, 70.8%, and 70.8%, respectively, in the ⬍3 mm group (Fig 4). At 6 months, the minimum and maximum internal diameters of vein grafts in the ⬍3 mm group were 2.6 to 6.3 mm (median, 3.9 mm). This is in comparison to the preoperative minimum and maximum internal diameter of 2 to 2.9 mm (median, 2.5 mm). There were four occluded grafts in the ⬍3 mm group and five both in the ⬎3 mm group. The indication for surgery in the ⬍3 mm group was for non-healing ulcers with damped waveforms in the crural vessels. By the time the grafts occluded (139-204 days after the procedure), the ulcers had healed and did not result in limb loss. Conversely, in the ⱖ3 mm group, of the five occlusions, there were four major amputations. These were in 2 patients with dorsalis pedis bypass, 1 patient had uncontrolled sepsis and 1 patient for iatrogenic injury to the graft during salvage angioplasty; this resulted in complete graft occlusion and runoff thrombosis.

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Fig 3. Secondary patency rates in both groups.

Fig 4. Amputation-free survival in both groups.

DISCUSSION There is a general consensus that venous grafts should be used in infra-inguinal bypass grafting whenever possible.9 The conduit of choice is the autogenous GSV, which has proven to be superior to alternative grafts in terms of patency and complication rates.1-4 A recent large study by Pomposelli et al4 on pedal arch bypasses and Klinkert et al1 on above knee femoropopliteal bypasses, clearly showed superiority of GSV versus expanded polytetrafluoroethylene grafts with secondary patency rates at 5 years of 67.6% compared to 46% in the former study and 79.7% compared to 57.2% in the later. The importance of preoperative evaluation of potential venous conduits before infra-inguinal revascularization has been recognized since the 1970s. Previous authors have realized the value of venography in identifying anomalies and disease processes that would prevent the use of veins as

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arterial bypass grafts. It also identified the best available venous segment, thereby reducing unnecessary incisions and minimizing operating time.10,11 However, venography is inaccurate at estimating vein diameter, and does not allow identification of vein depth or position relative to fascial structures.10 In the 1980s, real-time B-mode ultrasonography scan proved to be a successful noninvasive technique for preoperative evaluation of potential venous conduits before infra-inguinal revascularization. It provides anatomic information, including size, patency, course, varicosities, duplicated segments, and tributaries.12 Ultrasonography has an accuracy of 98% and predictive value of detecting usable veins in 96% of cases.13,14 The smallest acceptable diameter of a vein graft remains controversial. A previous study reported cumulative patency rates for ⱖ3 mm and ⬍3 mm vein grafts at 1 year of 53% and 20%, respectively.5 The Project or Ex-Vivo vein graft Engineering via Transfection III trial also suggested that vein grafts ⬍3.5 mm in diameter had an overall poor outcome.7 In the absence of a suitable GSV, other autogenous veins have shown good long-term patency and limb salvage rates.15,16 In a large study by Faries et al,17 autogenous arm vein grafts demonstrated higher patency and limb salvage rates compared with prosthetic grafts. This difference achieved statistical significance in both femoro-belowknee-popliteal and femoro-tibial bypasses. The authors of the current series preferred to use ⬍3 mm GSVs to avoid long and extra incisions in the arms, and leg veins have better wall quality compared to arm veins.4 The authors are especially keen to avoid prosthetic grafts mainly because of the increased risk of graft infection in our cohort, which includes high prevalence of diabetes mellitus (72.0%), renal failure (25.5%), tissue loss (54.4%), and gangrene (25.7%). Other conduits such as cryopreserved saphenous vein allografts have been suggested as a valuable alternative. Although early reports showed poor long-term patency rates with secondary cumulative graft patency rates of only 40% at 1 year,18 a recent study by Randon et al19 reported primary and secondary patency rates of 56% and 73% at 1 year and of 32% and 60% at 3 years, respectively. However, raising concerns about the shortage in these grafts’ availability might limit their widespread use. It is widely advocated that the vein diameter may influence patency rates and, hence, most authors recommend the use of veins of a diameter of 3.5 mm or more as a minimum size requirement.5,6 The outcome in terms of graft patency rate in the current series using autogenous veins ⬍3 mm is considerably better than that reported in the Project or Ex-Vivo vein graft Engineering via Transfection III trial with a cumulative secondary patency rate of only 63% at 1 year.7 Although there was a significant difference in the secondary patency rate at 1 year in our series, however, this patency rate of 82.6% in the ⬍3 mm group compares well to the cumulative patency rate of 78% at 1 year reported by Wengerter et al5 in veins with a large diameter (⬎4 mm).5 It is possible that patency rates may

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diverge more significantly if there were longer follow-up. The relatively low primary patency rates in the current series can be explained by the high percentage of crural bypasses and the structured and meticulous duplex scan surveillance program picking up early graft abnormality requiring radiological or surgical intervention. The authors attribute the good patency rates of the ⬍3 mm grafts to maturation, dilatation, and arterialization of venous conduits as described before20,21 and also shown in the current series in which the median diameter of the vein at 6 months has increased to 3.9 mm from the original 2.5 mm. A clearly defined follow-up system with a meticulous duplex scan surveillance program has proven to be beneficial for graft patency related outcome.22 In the current series, the ⬍3 mm group had a higher number of threatened grafts identified during the surveillance program (40.6% compared to 26.9% in the ⱖ3 mm group); however, the need for secondary intervention was statistically insignificant between the two groups (P ⫽ .122). Timely intervention in threatened grafts has shown to improve long-term patency. A recent study reported a 3-year assisted primary patency rate of 91% using arm veins where angioplasty was being performed in nearly half of all grafts.22 As parameters for the functional outcome, the 1-year amputation-free survival and patency rate were chosen. The outcome in both groups showed no significant difference. In fact, a lesser percentage of patients did require major limb amputation in the small vein group. However, the authors acknowledge the fact that this may be an effect of the small sample size in this group. CONCLUSION This series has shown that primary and assisted primary patency rates in small veins are not significantly different at 1 year but the secondary patency rates are better in the larger veins. Similarly, the amputation-free survival was also comparable. The authors would, therefore, advocate the use of small veins ⬎2 mm in diameter in patients with CLI. Duplex scan surveillance followed by early salvage angioplasty for threatened grafts is needed to achieve good patency rates in both groups. AUTHOR CONTRIBUTIONS Conception and design: HR Analysis and interpretation: HS, AT, HR, JR Data collection: HS Writing the article: HS, AT, HR, JR Critical revision of the article: HR Final approval of the article: HS, HR, AT Statistical analysis: HS, AT Obtained funding: Not applicable Overall responsibility: HS, HR

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REFERENCES 1. Klinkert P, Schepers A, Burger DH, van Bockel JH, Breslau PJ. Vein versus polytetrafluoroethylene in above-knee femoropopliteal bypass grafting: fiveyear results of a randomized controlled trial. J Vasc Surg 2003;37:149-55. 2. Albers M, Romiti M, Brochado-Neto FC, De Luccia N, Pereira CA. Meta-analysis of popliteal-to-distal vein bypass grafts for critical ischemia. J Vasc Surg 2006;43:498-503. 3. Dormandy JA, Rutherford RB. Management of peripheral arterial disease (PAD). TASC Working Group. TransAtlantic Inter-Society Consensus (TASC). J Vasc Surg 2000;31(1 Pt 2):S1-296. 4. Pomposelli FB, Kansal N, Hamdan AD, Belfield A, Sheahan M, Campbell DR, et al. A decade of experience with dorsalis pedis artery bypass: analysis of outcome in more than 1000 cases. J Vasc Surg 2003;37:307-15. 5. Wengerter KR, Veith FJ, Gupta SK, Ascer E, Rivers SP. Influence of vein size (diameter) on infrapopliteal reversed vein graft patency. J Vasc Surg 1990;11:525-31. 6. Idu MM, Buth J, Hop WC, Cuypers P, van de Pavoordt ED, Tordoir JM. Factors influencing the development of vein-graft stenosis and their significance for clinical management. Eur J Vasc Endovasc Surg 1999;17:15-21. 7. Schanzer A, Hevelone N, Owens CD, Belkin M, Bandyk DF, Clowes AW, et al. Technical factors affecting autogenous vein graft failure: observations from a large multicenter trial. J Vasc Surg 2007;46:1180-90; discussion 1190. 8. Rutherford RB, Baker JD, Ernst C, Johnston KW, Porter JM, Ahn S, et al. Recommended standards for reports dealing with lower extremity ischemia: revised version. J Vasc Surg 1997;26:517-38. 9. Adam DJ, Beard JD, Cleveland T, Bell J, Bradbury AW, Forbes JF, et al. Bypass versus angioplasty in severe ischaemia of the leg (BASIL): multicentre randomised controlled trial. Lancet 2005;366:1925-34. 10. Veith FJ, Moss CM, Sprayregen S, Montefusco C. Preoperative saphenous venography in arterial reconstructive surgery of the lower extremity. Surgery 1979;85:253-6. 11. Mosley JG, Manhire AR, Raphael M, Marston JA. An assessment of long saphenous venography to evaluate the saphenous vein for femoropopliteal bypass. Br J Surg 1983;70:673-4. 12. Ruoff BA, Cranley JJ, Hannan LA, Aseffa N, Karkow WS, Stedje KG, et al. Real-time duplex ultrasound mapping of the greater saphenous vein before in situ infrainguinal revascularization. J Vasc Surg 1987;6:107-13. 13. Bagi P, Schroeder T, Sillesen H, Lorentzen JE. Real time B-mode mapping of the greater saphenous vein. Eur J Vasc Surg 1989;3:103-5. 14. Seeger JM, Schmidt JH, Flynn TC. Preoperative saphenous and cephalic vein mapping as an adjunct to reconstructive arterial surgery. Ann Surg 1987;205:733-9. 15. Brochado-Neto FCa, Albers M, Pereira CA, Gonzalez J, Cinelli M Jr. Prospective comparison of arm veins and greater saphenous veins as infrageniculate bypass grafts. Eur J Vasc Endovasc Surg 2001;22:146-51. 16. Faries PL, Arora S, Pomposelli FB Jr, Pulling MC, Smakowski P, Rohan DI, et al. The use of arm vein in lower-extremity revascularization: results of 520 procedures performed in eight years. J Vasc Surg 2000;31(1 Pt 1):50-9. 17. Faries PL, Logerfo FW, Arora S, Hook S, Pulling MC, Akbari CM, et al. A comparative study of alternative conduits for lower extremity revascularization: all-autogenous conduit versus prosthetic grafts. J Vasc Surg 2000;32:1080-90. 18. Martin RS 3rd, Edwards WH, Mulherin JL Jr, Edwards WH Jr, Jenkins JM, Hoff SJ. Cryopreserved saphenous vein allografts for below-knee lower extremity revascularization. Ann Surg 1994;219:664-70; discussion 670-2. 19. Randon C, Jacobs B, De Ryck F, Beele H, Vermassen F. Fifteen years of infrapopliteal arterial reconstructions with cryopreserved venous allografts for limb salvage. J Vasc Surg 2010;51:869-77. 20. Head HD, Brown MF. Preoperative vein mapping for coronary artery bypass operations. Ann Thorac Surg 1995;59:144-8. 21. Owens CD, Rybicki FJ, Wake N, Schanzer A, Mitsouras D, Gerhard-Herman MD, et al. Early remodeling of lower extremity vein grafts: inflammation influences biomechanical adaptation. J Vasc Surg 2008;47:1235-42. 22. Armstrong PA, Bandyk DF, Wilson JS, Shames ML, Johnson BL, Back MR. Optimizing infrainguinal arm vein bypass patency with duplex ultrasound surveillance and endovascular therapy. J Vasc Surg 2004;40:724-30; discussion 730-1. Submitted Jun 7, 2010; accepted Sep 2, 2010.