I
ntroductIonAlthough the fistula-first strategy has been recognized as the treatment of choice regarding dialysis access creation, synthetic hemodialysis Arterio-Venous Grafts (AVGs) con-stitute the so called “lifeline” for most dialysis patients in the United States and are mainly used after failed fistulas or as a “passage” to native fistulas (1, 2). However, they are characterized by a high failure rate, mainly because of stenosis occurring at their venous anastomotic site and/or outflow veins, resulting in a decline of flow and subsequent thrombosis (3, 4). A well-established method to preserve failing dialysis accesses is percutaneous transluminal an-gioplasty (PTA) (5, 6). Nevertheless, the one-year primary patency rate following PTA of newly placed synthetic AVGs is approximately 25%, while secondary patency rates up to 50% at three years, have been reported (7). In an attempt to improve immediate technical success patency rates, bare metal stents have been widely used both as a primary and bail-out solution following plain PTA, but until today their be-nefit over balloon angioplasty remains to be proven (8-10). More recently, a multicenter, randomized, study has advo-cated the use of covered stents in treating stenosis of the venous anastomosis for percutaneous revision of failing
A
bstrActBackground: A well-established method to preserve failing synthetic arteriovenous grafts (AVGs) dialysis accesses is percutaneous transluminal angioplasty (PTA). Nevertheless, the one-year primary patency rate following PTA is approximately 25%. This study was designed to compare the angiographic and clini-cal outcomes following stent-graft insertion versus angioplasty and/or bare metal stenting (BMS) of recur-rently failing AVGs, because of anastomotic and/or ve-nous outflow stenoses.
Methods: Self-expanding stent-grafts were deployed for the treatment of failing AVGs in case of recurrent stenosis after treatment with conventional angioplasty or bail-out BMS. Regular angiographic follow-up was scheduled every two months the first six months and every three months thereafter. Data from previous procedures on the same treatment site were retrieved from our database. Primary patency was defined as a functioning graft with a patent treatment site without angiographic restenosis >50% and without any sub-sequent repeat procedures. Outcome data were ana-lyzed by Kaplan-Meier analysis.
Results: In total, 35 patients previously treated with angioplasty and/or BMS for the treatment of recurrent significant AVG stenosis (group PTA), underwent stent-graft placement of the same treatment site (group SG). Of those, 20 patients had undergone angioplasty and 15 bail-out BMS. Mean lesion length was 4.8±1.7cm. Prima-ry patency was significantly improved in the SG group (Hazard Ratio [HR] = 0.2 [95% CI= 0.11-0.36], P=.0001) by log-rank test. The estimated six and 12-month pa-tency rates were 76.9% vs. 25.7%, and 61.4% vs. 8.6% for groups SG and PTA respectively, (P<.0001).
Department of Interventional Radiology, Patras University Hospital, School of Medicine, Rion - Greece
Dimitris Karnabatidis, Panagiotis Kitrou, Stavros Spiliopoulos, Konstantinos Katsanos, Athanasios Diamantopoulos, Nikolaos Christeas, Dimitris Siablis
Stent-grafts versus angioplasty and/or bare
metal stents for failing arteriovenous grafts:
a cross-over longitudinal study
Conclusions: Stent-graft placement significantly im-proves primary patency of anastomotic and venous outflow stenoses in recurrently failing prosthetic arte-riovenous grafts.
Key words: Arteriovenous graft, Balloon angioplasty, Bare metal stent, Covered stent, Failing dialysis access, Hemodialysis, Stent-graft
dialysis grafts, demonstrating superior results when compa-red to balloon angioplasty (11). Use of stent-grafts or cove-red stents has therefore launched a new era of endovascular management of failing prosthetic dialysis circuits (12). We herein present the angiographic and clinical outcomes of a prospective study investigating the use of a self-expandable covered stent for the management of recurrent venous ana-stomotic stenosis of AVG grafts. The authors compare the one-year outcomes of stent-graft insertion in failing dialysis AVGs with those of angioplasty and/or bare metal stenting of the same treatment site.
M
AterIAlsAnd MethodsStudy design
Institutional Review Board approval was obtained by the Hospital’s Ethical and Scientific Committee. The study was performed in adherence with the Declaration of Helsinki. This was designed to be a prospective, single-center, cross-over study, in order to assess the angiographic and clinical outcomes of covered stent placement in the management of restenosis regarding the venous anastomosis site and/or outflow veins of failing hemodialysis prosthetic AVGs. The stent used was a self-expanding nitinol stent graft covered in carbon-impregnated expanded polytetrafluoroethylene (ePTFE) (The FLUENCY® Plus Vascular Stent Graft, Bard
Peripheral Vascular, Helsingborg, Sweden. Various types of non-compliant high pressure balloons, available in our department (Blue Max PTA, Boston Scientific, Natick, MA, USA; Dorado PTA balloon dilatators catheter, Bard Periph-eral Vascular, Tempe, AZ, USA) as well as various bare metal stents (SMART Nitinol Stent, Cordis Endovascular, JNJ, USA; PROTEGE EverFlex, EV3, Plymouth, USA) had been previously applied in the patient cohort before crossing over to stent-graft treatment. All eligible patients signed the writ-ten informed consent form and were included in the study. As this was a cross-over trial of patients undergoing stent-graft treatment, the primary inclusion criterion was that all patients scheduled to receive a stent graft should have been previously subjected to PTA and/or BMS of the same treatment site. After stent graft treatment, the same patients were divided into two groups according to their previous endovascular treatment. Group PTA included the patients previously treated with PTA and/or bail-out bare metal ing, and group SG included the same patients after stent-graft placement for recurrent stenosis following the previ-ous either PTA or BMS treatment. Further inclusion criteria comprised a failing AVG with any of the following signs:
de-tection of elevated venous pressure during dialysis and/or intra-access blood flow less than 600 mL/min, associated with an angiographically diagnosed ≥50% restenosis of the graft-venous anastomosis, while exclusion criteria included graft infection, and severe cardiopulmonary disease (2). The patients’ demographics, procedural details, and follow-up imaging were recorded in the department’s database.
Endpoints and definitions
The study’s primary endpoints included technical success defined as a <30% residual stenosis and lesion primary patency defined as a functional AVG lesion site without any significant restenosis or repeat procedures of the tre-atment site. Clinical success was defined as the ability to use the AVG for at least one successful dialysis session following treatment with successful relief of the patient’s symptoms. Lesion primary patency was lost in case of any angiographically proven restenosis within the treated lesion area, and/or clinically-driven target lesion re-intervention, or graft thrombosis. Angiographic restenosis was set at a 70% threshold; clinically driven re-intervention was defined as the percutaneous or surgical treatment of a ≥50% target lesion restenosis associated with clinical and/or hemodyna-mic abnormality of the graft, while thrombosis was clinically assessed as the presentation of an impalpable graft, re-sulting in the inability to perform hemodialysis. Both resi-dual stenosis and restenosis were assessed by QVA (Allura FD20, Philips Medical Systems, Germany) following digital subtraction angiography (DSA). Secondary endpoints inclu-ded the AVG survival defined as the overall time period that the AVG access was used for dialysis, since the day this was created and the procedure-related complication rates. Complications were classified as major or minor according to the international reporting standards (13).
Procedure
Providing that all of the study’s criteria were met, prior to the procedure the performing physician obtained a detai-led physical examination and history of the patient and the AVG. A single, intravenous dose of prophylactic antibiotic— usually cefazolin sodium—was administered. The percuta-neous access was performed in a suitably chosen site of the synthetic graft with the use of a micro puncture set (Vena-stick™ Set, Angiotech, PBN Medicals, Denmark), followed by the placement of a 6Fr vascular sheath. A selective DSA of the graft in order to delineate the venous anastomotic le-sion and the outflow central veins was performed. The lele-sion was crossed using standard interventional radiology
cathe-ters and guide-wires, while the size of the balloon or stent graft (diameter and length) was selected according to ves-sel analysis measurements. In the control groups PTA was performed with the use of appropriately sized high-pressure balloons for a time period between one and three minutes and a bare metal stent was used, following a second pro-longed balloon inflation, in cases of suboptimal angioplasty with elastic recoil or residual stenosis >30%. In group SG, the target lesion was pre-dilated because of the very tight fibrotic properties of the stenoses and post-dilated in cases of sub-optimal graft expansion resulting in ≥ 30% remaining luminal stenosis. A final angiography of the entire AVG ac-cess, including the vein outflow and the arterial inflow, was performed. After completion of the procedure hemostasis was achieved with the use of a purse-string suture techni-que (14). Patients received anti-platelet therapy with clopi-dogrel 75 mg daily for life, while regular clinical surveillance and angiographic follow-up was set every two months for the first six months and biannually thereafter, unless dialysis adequacy indicated otherwise.
Statistical analysis
Discrete variables were expressed as counts and percent-ages and continuous variables were given as medians with interquartile ranges (i.e., between the 25th and 75th per-centiles) in parentheses or as means ± standard deviation if they passed the normality test. The Kolmogorov-Smirnov goodness-of-fit test was utilized to determine if continuous data followed a normal distribution. The unpaired student t test was used to test the statistical significance of difference of variables that passed the normality test. The Mann-Whit-ney test was used for qualitative variables and for non-para-metric testing of continuous variables that did not pass the normality test. Comparison of proportions was performed using the chi-square test. The threshold of statistical sig-nificance was set at 5% (P= .05). Life-table analysis with the Kaplan-Meier method was employed for calculation of the cumulative proportion outcomes. Pairwise comparison of the Kaplan-Meier curves was performed with the log rank test. Results were stratified according to the type of treat-ment (PTA vs. SG). Statistical analysis was performed with use of the GraphPad PRISM statistical software package (5th edition, San Diego, California, USA).
r
esultsIn total, 35 patients (21 men, 67.8±14.3 years), treated be-tween April 2009 and January 2011, met the protocol’s cri-teria and were included in the study. All failing AVGs with
re-current anastomotic and outflow stenosis were treated with self-expanding Fluency stent-graft devices. All procedures were performed in synthetic AVGs. Of those, 20 patients had undergone plain balloon angioplasty and 15 patients underwent angioplasty and BMS of the same treatment site in the past. In most cases upper extremity AVG were treated (33/35), while two patients had a lower extremity AVG (2/35). The majority were straight grafts (33/35, 94.3%), while only two loop grafts were treated (5.7%). Thirty-three stent-grafts were inserted into the venous-graft anastomotic site and four in central venous outflow stenotic lesions for a total of 37 Fluency devices as two subjects received two overlap-ping stent-grafts. In one case the second overlapoverlap-ping graft was necessary in order to completely cover the stenosis and in the second case the second graft was deployed be-cause of the inaccurate deployment of the first one.
The mean AVG age at the time of treatment was 26.4 ± 20.6 months (range 1.2 – 92.4 months) for group PTA and 40.4 ± 22.9 months (range 6 – 105.6 months) for group SG. Mean length of treated lesions was 4.8±1.7cm (range 1.0- 8.5 cm). The diameter and length of the stent grafts ranged between 7 to 12 mm and 40 to 100 mm, respective-ly, while most grafts (34/37, 91.9%) were deployed through an 8 or 9 French sheath according to instructions for use. Patients’ baseline demographics, dialysis access, and stent graft details are analytically reported in Tables I and II. The technical and clinical success rates in all study groups were 100%. There were no procedure-related major com-plications associated with any of the procedures. Minor complications included two small puncture-site related he-matomas (2/35, 5.7%). Primary patency was significantly better in the SG group [Hazard Ratio (HR) = 0.2 (95% CI= 0.11-0.36], P=.0001 by log-rank test. The estimated six and 12-month patency rates were 76.9% vs. 25.7%, and 61.4% vs. 8.6% for the SG and PTA groups, respectively (P<.0001) (Fig. 1). Overall dialysis survival rate was 100% as all AVGs circuits (35/35) were functional at the completion of the study. The study’s endpoints are presented in Table III.
d
IscussIonKeeping AVG patent is the crucial objective when treating hemodialysis patients and the main hazard to this enduring, demanding effort, is venous anastomosis stenosis (3, 4, 7, 15). Balloon angioplasty, which has been considered for many years as the gold standard percutaneous endovascu-lar method for the management of failing dialysis access, is generally associated with poor mid- and long-term patency rates (3, 16-18). As a result, several clinical trials advoca-ted alternative instruments to ameliorate long-term graft
pa-TABLE I
BASELINE CHARACTERISTICS OF STUDY PATIENTS AND DIALYSIS ACCESS CIRCUITS
Age (years) 67.8±14.3 (range, 30-95 y)
Male sex 16/35 (45.7)
Side of dialysis access (Right/total) 10/35 (28.6)
Body region 33 upper arm / 2 upper leg (94.3/5.7)
Configuration of synthetic graft 33 straight / 2 loops (94.3/5.7) Cause of renal failure:
• Diabetes 8/35 (22.9) • Hypertension 2/35 (5.7) • Polycystic kidney disease PKD 3/35 (8.6) • SLE Nephropathy 1/20 (2.9) • Unknown 15/35 (42.9) • Other 9/35 (25.7)
Index lesion length (cm) 4.8±1.7 cm (range, 1.0-8.5 cm)
Baseline variables were registered at the time of the first intervention of the target site.
TABLE II
FLUENCY ePTFE STENT GRAFT LOCATION, DIAMETERS, AND LENGTHS
Diameter/Sheath Anatomic location Number Length (mm) Number
7 mm/8 Fr Venous anastomosis 4 40 14
8 mm/9 Fr Venous anastomosis 17 60 15
9 mm/ 9 Fr Venous anastomosis/ outflow vein 13 80 7
10 mm/9 Fr Outflow vein 2 100 1
12 mm/10 Fr Outflow vein 1
tency such as bare metal stents, cutting balloons, and cryo-plasty, but to date none has proved to be superior to plain balloon angioplasty (10, 19-21). Especially regarding bare metal stents, the 2000 National Kidney Foundation’s Dialysis Outcome Quality Initiative (K-DOQI) Vascular Access Clinical Practice Guidelines, reported that stenting should be reser-ved as a bail-out solution following suboptimal or compli-cated PTA (22). Nonetheless, several studies have reported that the use of nitinol, self-expanding, bare metal stents in venous stenosis may achieve highly superior primary pa-tency rates compared to previous generation stainless steel
stents (23, 24). In a recent multicenter, controlled trial, Haskal et al compared the effectiveness of “traditional” PTA with that of PTA followed by the insertion of stent graft at the ste-nosed venous anastomosis site. The primary endpoints in-cluded patency of the treated area and patency of the entire vascular access unit. Both six-month primary treatment site patency and primary access circuit patency rates were ap-proximately double in the stent-graft group (11). This study marked the beginning of a new era in the endovascular ma-nagement of failing AVG access, as several other multicen-ter trials such as RENOVA and REVISE are now underway,
which aim to strengthen high-level scientific evidence about the use of stent grafts for the treatment of AVG stenosis. In keeping with the aforementioned optimistic results Chan MG et al moved a step forward and recently reported the initial results following the utilization of a heparin-coated self-ex-pandable stent graft for the treatment of refractory dialysis access circuits, demonstrating significantly superior results compared to conventional stent-grafts (six-month primary patency rates 57% vs. 11%, P=.06, respectively) (25). This is a cross-over study designed to compare the estab-lished interventional approach for failing dialysis access, that of balloon angioplasty and/or bail out stenting with the
newly proposed covered stents. A cross-over study has the advantage of reduced influence of confounding covariates as each cross-over subject also serves as its own control and the new treatment is applied and compared to the old one on the same patient, the same dialysis access, and on the same treatment site (26). Our results demonstrated a significantly superior one-year target lesion primary patency in the stent-graft group, almost five times higher compared to the use of plain balloon angioplasty and/or bail-out bare metal stents (Fig. 1). Moreover, the patency rates reported herein have resulted from a combined angiographic and clinical follow-up scheme as opposed to most studies that have only used the dialysis access function as the primary endpoint (27, 28). Of note, international guidelines suggest that the acceptable unassisted patency rate of an AVG ste-nosis following successful PTA is 50% at six months, while in this study the 12-month unassisted patency in group SG was above 65% according to rigorous follow-up (22). On the other hand, the technical success and overall access survival rates in both study groups was equal (100%), sug-gesting that both percutaneous methods are equally feasi-ble and safe in the treatment of failing AVG dialysis access. Nonetheless, the superior patency outcomes of the revision of a venous anastomotic stenosis with a covered stent may be attributed to the minimization of elastic recoil and tissue in-growth as compared with that following balloon angio-plasty and bare metal stenting. Moreover the specific graft is constructed with the same material as the AVG. Thus, its application could be considered as the percutaneous en-dovascular minimally invasive extension of the pre-existing graft, imitating the surgical revision of the access without sutures, allowing at the same time immediate access us-age, and avoiding interim placement of an additional dialy-sis catheter. In particular, the majority of re-stenotic lesions in group SG were noted at the edges of the covered stent, while in our experience most of the late thrombotic events
Fig. 1 - Kaplan-Meier analysis of lesion primary patency up to 24 months of follow-up. Note the significantly improved patency outcomes in case of the lesions treated with stent-graft placement.
TABLE III
STUDY ENDPOINTS
Endpoint Group PTA Group SG (log-rank)P
Technical success 100% 100% n/a
12-month target lesion primary patency 8.6% 61.4% <.0001 Major procedure- related complications None (0.0%) None (0.0%) n/a
Fig. 2 - Representative case of recurrent anastomotic AVG stricture treated with stent-graft placement. A) Recurrent he-modynamically significant stenosis four months after place-ment of a self-expanding BMS at the level of the venous anastomotic site (white arrowhead). B) Lesion was treated with repeat balloon pre-dilation and placement of an 8 x 80 mm Flunecy device (white double arrow). C) Follow-up an-giogram six months later reveals a widely patent AVG without any signs of recurrent stenosis (white double arrow).
occurred in cases where the stent graft was deployed just adjacent to a venous valve and we tried to avoid that with the use of longer SGs. Hence, it is strongly recommended that the stent-graft should be long enough to cover any ve-nous valve in proximity to its distal edge.
Of note, in four cases the stent graft was positioned in the outflow vein just distally to the vein-graft anastomosis and no further than the mid segment of the axillary vein. These patients were symptomatic according to the inclusion cri-teria, with a >70% stenosis diagnosed during intra-proce-dural DSA. As no other in-graft and/or anastomotic stenosis was detected, the graft dialysis dysfunction was attributed to the venous outflow stenosis. At this point it should be underlined that owing to the nature of the study, the only continuously changing parameter between the two groups was the age of the dialysis access, as the same patients were first managed with PTA and/or BMS and subsequently with stent-grafts. This resulted in a significantly higher age of AVG dialysis circuits in the stent graft group. However, this fact should represent an inherent bias in favor of the control PTA group, as younger AVGs have been subjected to less use and therefore less punctures, less declotting pro-cedures, and have developed less pseudoaneurysms and heavily fibrotic lesions, all of which may normally contribute to a decline in the expected AVG survival. On the contrary, this study demonstrates that even after a long period of con-tinuous percutaneous efforts to maintain AVG function, the application of a self-expandable covered stent significantly reduced re-intervention procedures and improved patency of the AVG treated sites (Fig. 2). Subsequent to this study, our department’s protocol routinely endorses the primary deployment of a stent-graft in all stenotic venous anasto-motic sites of synthetic AVG and annual imaging follow-up visits have been reduced from six to three on average.
This study’s limitations include its single-center nature and the small number of patients included. Moreover, because of the study design, a selection bias cannot be excluded. However, optimal crossover designs are statistically efficient and therefore may require fewer subjects than non-cross-over trials (29). In addition, the design of this study is more representative of real-life endovascular management of fail-ing dialysis grafts. To sum up, in this sfail-ingle center, cross-over study, the percutaneous insertion of self-expandable stent grafts for the management of venous anastomotic site stenosis resulting in failing dialysis AVG access demonstrat-ed significantly superior long-term angiographic primary patency rates and decreased need for repeat procedure in comparison with conventional balloon angioplasty and/or bail-out bare metal stents. In conclusion, stent-graft place-ment significantly improved the primary patency of recurrent stenoses of failing prosthetic arteriovenous grafts. Larger trials are needed in order to provide valid conclusions.
Financial support: None.
Conflict of interest statement: The authors declare that they have no conflict of interest.
Address for correspondence: Dimitris Karnabatidis
Assistant Professor of Interventional Radiology Department of Interventional Radiology Patras University Hospital
School of Medicine Rion, 26504, Greece [email protected]
r
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