Journal of Vascular Surgery
Volume 49, Issue 3 , Pages 589-595, March 2009

Late conversion of aortic stent grafts

Presented at Society for Vascular Surgery Annual Meeting, San Diego, Calif, Jun 7, 2008.

Department of Vascular Surgery, Cleveland Clinic Foundation, Cleveland, Ohio

Received 6 August 2008; accepted 11 October 2008. published online 12 January 2009.

Article Outline

Objectives

The frequency of late removal of endovascular abdominal aortic repair (EVAR) parallels the rise of endovascular aortic repair. Evaluation of outcomes for EVAR explants may identify risks for complications and alter clinical management.

Methods

A patient database was used to identify EVAR patients requiring explant >1 month after implant. A retrospective analysis was conducted of the type of graft, duration of implant, reason for removal, operative technique, death, and length of stay.

Results

During 1999 through 2007, 1606 EVARs were performed, and 25 patients required explantation, with an additional 16 referred from other institutions (N = 41). The average age was 73 years (range, 50-87 years); 90% were men. Grafts were excised after a median of 33.3 months (range, 3-93 months). Explanted grafts included 16 AneuRx (40%), 7 Ancure (17%), 6 Excluder (15%), 4 Zenith (10%), 4 Talent (10%), 1 Cook Aortomonoiliac rupture graft, 1 Endologix, 1 Quantum LP, and 1 homemade tube graft. Overall hospital mortality was 19% and occurred after conversion for rupture in 4, and in infected graft, aortoenteric fistula, repair of new aneurysm of the visceral segment, and claudication due to graft stenosis in one patient each. Elective EVAR-related mortality was 3.3%. Mortality was higher in patients with rupture compared with nonrupture (4 of 6 vs 3 of 35, P ≤ .01). Thirty patients (73%) had one or more endoleaks (type I, 16; II, 9; III, 9; endotension, 5). Migration (n = 10), rupture (n = 6), aortoenteric fistula (n = 3), infection (n = 1), limb thrombosis (n = 3), and claudication (n =1) were also factors. Proximal aortic control was above the endograft (supravisceral, 23; suprarenal, 12; infrarenal, 6). Reconstruction was an aortoiliac repair in 63% and tube graft in 25%. Grafts with suprarenal fixation required longer proximal aortic clamp time of 43 minutes vs 28 minutes for infrarenal fixation. Complete graft removal was achieved in 85%. Proximal or distal portions of the endograft were incorporated into the repair in the remaining six.

Conclusion

Elective EVAR conversion, although technically challenging may be done with mortality similar to primary open repair. Mortality for conversion for infected grafts and ruptured aneurysms remains high. EVAR is associated with continued risk of conversion, and surveillance may identify late complications that require removal, justifying lifelong monitoring. Aggressive management of late complications and elective conversion may minimize the mortality associated with this procedure.

 

Endovascular aortic abdominal aneurysm repair (EVAR) has quickly gained popularity for infrarenal aortic aneurysm (AAA) repair during the last 2 decades. EVAR has been proven safe and effective in repair of AAA patients.1, 2, 3, 4, 5, 6 Successful EVAR for AAA has improved with growing physician experience and increased understanding of the limitations of different devices. Although long-term durability of EVAR remains a concern among physicians and patients alike, many of the complications after EVAR are successfully addressed with endovascular means.

Late or secondary conversions are needed for a variety of reasons, including endoleaks that are not amenable to endoluminal therapy, graft infection, rupture, migration, and limb thrombosis.7 The rate of secondary conversions has been reported as 0% to 9% in EVAR series,3, 4, 5, 6, 8, 9, 10, 11, 12, 13, 14, 15 and the risk increases over time. Our previously reported incidence of conversion is 1.7%, with no significant difference in frequency amongst all devices used.16 Overall mortality from late conversion is markedly higher than primary elective open aneurysm repair and is influenced by rupture and infection. Compiled data from published series on surgical conversion report an average mortality rate of 22%.17 We review our experience with late conversions of AAA stent grafts to identify risks for complications, outcomes, and technical factors that may alter clinical management.

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Methods 

A patient database at the Cleveland Clinic Foundation was used to identify all patients who underwent an EVAR endograft explant during 1999 to 2007 by Current Procedural Terminology (CPT) and International Classification of Disease-9 revision (ICD-9) codes. Late conversion was defined as graft removal >1 month after implant of an endograft. Patients were excluded from analysis if conversion was performed at the time of the initial endograft placement or ≤1 month of placement. Patients with open repair of endoleaks or other attempts at increasing fixation without explant of the graft were also excluded.

Type of endograft, duration of implant, reason for removal, operative technique, mortality, and length of stay were identified. Reasons for removal in the analysis included endoleaks (stratified by type),18 migration, rupture, thrombosis, and enlargement of the aneurysm >5 mm. Operative factors included surgical approach, position, and duration of the proximal aortic cross-clamp, type of reconstruction, and blood loss. Statistical analysis was then performed using Excel 2003 (Microsoft, Redmond, Wash), the t test, and exact Pearson χ2 testing. Significance was identified for P ≤ .05.

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Results 

During the 8-year period from October 1999 to December 2007, 1606 EVARs were performed at the Cleveland Clinic. During this same interval, 41 patients were identified who required EVAR explant. Of these, 16 patients (39%) underwent endograft placement at other institutions were referred for management. Patients were an average age of 73 years (range, 50-87 years), and 90% were men.

Grafts were excised after a median of 33.3 months (range, 3-93 months) from the time of implant. Explanted grafts included 16 AneuRx (40%) and 4 Talent (10%; Medtronic AVE, Santa Rosa, Calif), 7 Ancure (17%; Guidant, Menlo Park, Calif), 6 Excluder (15%; W. L. Gore, Flagstaff, Ariz), 4 (10%) Zenith and 1 aortomonoiliac rupture graft (Cook Inc, Bloomington, Ind), 1 Powerlink (Endologix, Irvine, Calif), 1 Quantum LP (Cordis Corp, Miami Lakes, Fla), and 1 homemade tube graft. Conversions were performed by 11 different surgeons, with a median of three cases per surgeon (range, 1-6).

Average length of stay was 16 days (range, 1-56 days). Among the 25 endografts that were also implanted at the Cleveland Clinic were 9 AneuRx, 4 Excluder, 3 Talent, 3 Zenith, 2 Ancure, and 1 each of a Quantum LP, Homemade tube graft, and an aortomonoiliac rupture graft.

Explant was required for multiple indications, including endoleak, migration, aneurysm enlargement, rupture, infected graft, aortoenteric fistula, limb thrombosis, and claudication (Table I). In 76% of patients, there was more than one indication for conversion (mean, 2 ± 0.77). Five patients had more than one type of endoleak. Three patients had limb thrombosis as the indication for removal, one of whom presented with bilateral thrombosis and acute ischemia as the indication for repair.

Table I. Indications for explant (patients may have ≥1)
VariableNo. (%)
Patient total41(100)
Endoleak30(73)
Type I16(39)
Type II9(22)
Type III9(22)
Aneurysm growth30(73)
With endoleak25(83)
Without endoleak6(20)
Migration10(24)
Rupture6(15)
Aortoenteric fistula3(7)
Infected Graft1(2)
Limb thrombosis3(7)
Claudication1(2)

Before the explants took place, 25 patients underwent a mean of 1.6 ± 1.0 endovascular salvage interventions. Patients with an endovascular intervention to salvage their EVAR were primarily asymptomatic and diagnosed based on surveillance computed tomography (CT) scans. Compared with patients that did not have an intervention before their explant, patients who underwent secondary intervention of a late complications had a longer time from initial diagnosis of an endograft problem to the time of their explant (180 vs 833 days) and also had EVAR devices implanted for a longer time before removal (838 vs 1162 days).

Acute rupture was the presenting indication for explant in six patients (15%). All patients that presented with rupture had type I or type III endoleak or graft migration. Two of these were initially treated for a ruptured aneurysm with an EVAR, and both patients then presented with a second rupture requiring conversion as a result of a type I endoleak, aneurysm growth, and migration. The first patient was initially treated with a Cook two-piece aortomonoiliac rupture graft as part of a physician-sponsored investigational device exemption (IDE) use. Despite a 1-month follow-up CT scan without endoleak, he presented 6 months after implant with acute back pain and rupture. The second patient presented with rupture 4 years after his initial repair with an Ancure endograft with AneuRx extension limbs at another hospital.

There was an equal distribution of the approach used to remove the endograft: a retroperitoneal incision was used in 19 patients (46%) and a midline incision in 22 (54%). During the operation, once proximal and distal control was obtained, the sac was opened before clamping in most cases without clear reason for failure. This identified and confirmed the presence or absence and type of endoleak or other reason for failure of the endograft before clamping. Proximal aortic control was primarily above the endograft: supravisceral in 23, suprarenal in 12, and infrarenal in 6. Suprarenal or supravisceral clamping was used unless a sufficient distance existed between renal arteries and the beginning of the graft. The average renal ischemic clamp time for the proximal anastomosis was 33.4 ± 21.8 minutes. Endografts with suprarenal fixation required a longer proximal aortic clamp time of 43 minutes vs 28 minutes for infrarenal fixation (P = .39). There was no difference in outcome by multivariate analysis of graft type (Table II), including death, blood loss, clamp time, or renal failure.

Table II. The distributions of outcomes by graft type are shown a
VariableAncure, No. (%)AneuRx, No. (%)Zenith, No. (%)Excluder, No. (%)Talent, No. (%)P b
Total c716464
Endoleak4(57)14(88)3(75)2(33)3(75).19
Type I2(29)6(38)2(50) 2(50).41
Type II2(29)6(38) 1(17) .37
Type III1(14)6(38)1(25) 1(25).45
Aneurysm growth4(57)14(88)1(25)4(67)4(100).057
With endoleak3(75)13(93)1(25)2(50)3(75).40
Migration2(29)5(31)1(25) 1(25).70
Rupture1(14)3(19)1(25) .77
Aortoenteric fistula1(14)1(6) 1(17) .99
Infected graft 1(17) .38
Limb thrombosis2(29) 1(25) .096
Death2(29)3(19)1(25)1(17)1(25).99

aPatients may have ≥1 indication for explant.

bP is from an exact Pearson χ2 test.

cFour other grafts with N ≤1 were excluded from this analysis.

Primary reconstruction was an aortobiiliac repair in 63% and tube graft in 25%. The exception was patient who was converted after placement of a two-piece aortomonoiliac device and an established femoral–femoral bypass. No reconstruction was performed in two patients who died intraoperatively. Four additional reconstructions were performed in patients requiring a suprarenal repair and then either left renal reimplantion (n = 2) or left renal bypass (n = 2). One of these repairs was for a new aneurysm along the uncovered suprarenal segment of a Talent graft, which continued to exclude the infrarenal AAA component. This patient was repaired as a type IV thoracoabdominal repair and sewing distally into the stent graft main body with explant of the proximal graft and suprarenal fixation stent (Fig 1, C).

  • View full-size image.
  • Fig 1. 

    Hybrid reconstruction. Examples incorporating residual endografts into the aortic reconstruction. A, Incorporated proximal Zenith endograft into distal aortobiiliac repair. B, Proximal Dacron graft with distal AneuRx limbs. C, Bevelled proximal Dacron graft with left renal implant anastomosed to distal Talent endograft.

Four patients (10%) with aortoenteric fistulas or infected grafts underwent endograft removal and axillobifemoral bypass (n = 2), aortobifemoral bypass with bilateral femoral vein (n = 1), or no reconstruction owing to intraoperative death (n = 1).

Complete graft removal was achieved in 85%. In one patient after removal of both incorporated iliac limbs of an AneuRx endograft with a tube graft repair, there was inadequate distal flow due to an iliac dissection. This was treated with an aortoiliac bypass during the same operation. In six cases the stent graft was not completely removed and was incorporated into the proximal or distal portions of the repair. Stent grafts were not completely removed due to (1) aneurysmal progression of the suprarenal segment with AAA exclusion and good distal fixation, (2) difficulty removing a well-incorporated endograft both proximally and distally, and (3) isolated limb problem with good proximal fixation. Hybrid reconstructions were performed in these patients (Fig 1).

Average estimated blood loss was 6636 ± 5529 mL. There was no difference in blood loss in patients with suprarenal fixation compared with infrarenal fixation, those presenting with rupture (9500 mL) vs nonrupture (6082 mL; P = .23), or perioperative death (10,160 mL) vs alive (5987 mL; P = .33). Five patients required perioperative dialysis: four of 35 (11%) after suprarenal clamping and one of six (17%) after infrarenal clamping. One patient underwent aortorenal bypass as part of the reconstruction. Three of the renal failure patients died; two after emergency operation for presentation with rupture and one after an elective operation. Clamp location did not affect the risk of developing renal failure. No patient needed long-term dialysis after discharge, and only seven patients had a decrease in glomerular filtration rate (mean, 26% ± 18%) at the time of discharge.

Overall hospital mortality was 19% (8 of 41), with a 30-day mortality rate of 17% (7 of 41). Mortality was higher in patients with rupture compared with nonrupture (67% vs 9%, P ≤ .01). In patients who died, the indications for graft removal were four patients with rupture, and one patient each with infected graft, aortoenteric fistula, new aneurysmal changes of the visceral segment, and claudication due to graft stenosis.

After excluding emergency repairs for rupture, aortoduodenal fistula, graft infection, and the thoracoabdominal repair for visceral aneurysmal change above the original endograft, only one patient requiring elective conversion for an infrarenal AAA and EVAR-related problem died (mortality, 3.3%; Fig 2). This patient originally had an Excluder endograft, developed a type I proximal endoleak, and was treated with a Zenith Renu Aortouniiliac converter (AUI) and a TFLE 18-71 limb extension and femoral–femoral bypass, all at an another hospital. Graft occlusion of the AUI endograft occurred 1 month later, and he was treated with thrombolysis and angioplasty of the graft. Although this was successful, the narrowing of the TFLE limb within the Gore device caused disabling claudication and he underwent open aortobiiliac repair. The patient died on postoperative day 6 of a myocardial infarction.

  • View full-size image.
  • Fig 2. 

    Mortality of late conversion. Breakdown by urgency of operation shows high mortality for conversion occurring emergently, urgently, or with extensive reconstruction. EVAR, endovascular aneurysm repair.

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Discussion 

EVAR has revolutionized aortic surgery. Although the initial complication rate for infrarenal EVAR is lower than open repair, long-term follow-up data have confirmed the need for continued surveillance and secondary interventions to achieve complete exclusion. The rate of secondary intervention varies depending on the graft type and individual series, with a range from 8% to 42%.3, 8, 15, 19 No device has been immune to late failure requiring explantation, an observation that becomes more concerning with extended follow-up.9, 12

To our knowledge, this is the largest single-center series to date evaluating late conversion of EVAR. It is challenging to estimate the incidence of conversion, given that a significant percentage of the patients requiring conversion had undergone EVAR elsewhere and were simply referred in the setting of difficult complications. When evaluated in the context of devices implanted at this institution, the conversion rate approximates 1.6% (25 of 1606). Although an endovascular attempt at salvage of EVAR complications such as migration and endoleaks is a viable and often successful option for many patients, conversion is required for those that fail.

With increasing numbers of patients with EVARs undergoing longer follow-up, the incidence of conversion will undoubtedly rise, and thus defining outcomes with explant may help future patients. The indications for conversion are frequently multiple. The most common indications for explant, as expected, were aneurysm growth and endoleaks (Table I). Patients who undergo elective conversion fare much better than those presenting with rupture (67% vs 3% mortality). All patients presenting with rupture had type I or type III endoleaks and migration. Similar findings were noted in the European Collaborators on Stent-Graft Techniques for AAA and Thoracic Aortic Aneurysm and Dissection Repair (EUROSTAR) registry.13, 20 These observations stress the importance of detailed analysis of imaging studies after EVAR and an aggressive management stance on type I and III endoleaks as well as graft migration, whether endovascular or with conversion. Furthermore, in all patients with growing aneurysm—including those with type II endoleaks—we recommend conversion if patients are not candidates for endovascular salvage procedures or have failed intervention. We currently do not recommend conversion for type II endoleaks in the absence of AAA growth.

In this study we found no difference in explantation outcome when stratified by device type (Table II). With multiple different available aortic stent grafts, comparisons of conversion outcomes by graft type in future series may influence implant choices. Additional multivariate analysis of the risk of death based on the presence of suprarenal fixation also showed no difference. An overall hospital mortality of 19% is consistent with currently published data, but is an improvement over early series that noted mortality as high as 43%.1, 21 The risk of death is largely affected by the emergency and urgent cases for rupture and infection. Our mortality rate for elective conversion for AAA-related issues was 3.3% and compares favorably with the 5% to 8% mortality in observational and randomized controlled studies evaluating open repair.1, 2, 10, 22, 23 We believe that elective conversion in skilled hands can therefore be done with acceptable results and recommend early removal for failing EVAR before emergency or urgent repair is necessary.

Several technical considerations are important when performing a conversion. Previous research has recommended a retroperitoneal approach,12 and others a midline approach.9, 24 Both approaches were equally effective in this series, and their use largely depended on surgeon preference. Also, no association was found between clamp positions (suprarenal vs infrarenal) and perioperative hemodialysis. In general, endografts with proximal fixation problems were more likely to be approached from the side and require a suprarenal clamp. Once the graft was removed, the clamp position could be moved to the infrarenal location in many patients, limiting the renal and visceral ischemic insult.

Experience with endograft removal has also led to helpful maneuvers that assist in successful removal of the aortic stent graft, in addition to a traditional “clamp and pull” method. Several of these were used in this series on an individual basis. They included removing suprarenal fixation using metal cutters,7 collapsing the proximal fixation into a 20 mL syringe,25 and pouring iced saline on nitinol stents to help reduce size and ease removal. Wire cutters can be used not only to transect the barbed suprarenal stent of a Zenith graft but also to facilitate atraumatic removal at any point in devices with metal in the construct. After clamping, iced saline can be placed on nitinol elements to help collapse the metal to the predeployment state and ease removal from the arterial wall.

Technical challenges encountered during removal of endografts included incorporation of stents from endografts into the vessel wall, presence of external stents or barbs, and periaortic inflammation.7, 12, 26 We have observed increased periaortic inflammation with both active and passive fixation of endografts. This finding is unpredictable and not always present, however, even within similar graft types. To aid in removal of incorporated portions of endografts, we recommend secure aortic control above the area in question, removing the device piecemeal, or consideration of incorporating the EVAR device into a hybrid open repair.

Although complete graft removal is always the goal, incomplete removal is sometimes necessary. Early publications initially recommended against using a transected endograft as a part of the anastomosis because of concern regarding future pseudoaneursyms.9 In 2003, Lipsitz et al26 reported follow-up results from seven patients who underwent partial resection with a hybrid reconstruction. At an average of 22 months from time of explant, no patients have had anastomotic complications. Two technical points that they mention include incorporating native artery into the anastomosis as an additional buttress and tight closure of the aortic sac to minimize potential movement.26

Location of the endograft problem (proximal or distal), extent of the problem, and prevention of native tissue injury are important in deciding when not to remove the entire endograft. Portions of stents that are often difficult to remove, including barbs and small distal limbs with external stents, may be left in situ as long as they are not the culprits of endograft failure. These patients should continue with yearly endograft surveillance because future complications of remaining EVAR elements remain a possibility. A hybrid reconstruction using sections of well-incorporated graft may potentially improve survival by limiting the technical challenges and complications of a more extensive operation, but we believe complete removal of the endograft should be the goal of the procedure.

This study has several limitations. The largest is that this is a retrospective review that only evaluated patients who required conversion at our institution. We routinely monitor all patients treated with EVAR at our institution with either CT scan or ultrasound imaging at the discretion of the treating physician at 1 month after EVAR, 6 months, 1 year, and yearly thereafter.16 However, we are unable to ascertain with complete certainty the risk of conversion for patients we have treated, because all charts of patients treated with EVAR were not reviewed and the possibility that some patients may be lost to follow-up or required conversion at another hospital.

This study was unable to identify preoperative anatomic factors leading to graft failure and eventual conversion, because many of the preoperative CT scans were unavailable for review. Because CPT and ICD codes were used to identify patients, it is also not possible to evaluate how many patients avoided conversion because of successful endovascular therapies. Given the small number of observations and number of grafts explanted per stent type, there is insufficient power to identify differences using exact statistical analysis.

Another potential confounding factor is the changing availability of endografts and variable length of follow-up after implantation, which may affect the eventual conversion rates. Two notable examples are the removal of the Ancure device from the United States market and the change in the permeability of the Excluder material that appears to reduce or eliminate the risk of endotension.27, 28 Data from these endografts are incomplete, however, because surveillance and explantation of these devices continue to occur. Continued research and evaluation of explanted devices will provide larger sample sizes and, hopefully, further clinical information regarding indications for explant.

The future incidence of late conversion of endografts is changing. With increasing off label use, the limitations of graft design are being stretched and redefined. As interventionalists become more comfortable with EVAR devices and use devices in anatomy that is outside the instructions for use, we can expect to have inferior outcomes compared with data from IDE trials that may predispose some patients to late conversion. An important factor influencing the incidence of explants is graft durability; over time, the late risk of material fatigue will undoubtedly rise. Graft materials and construction are constantly undergoing testing to provide better configurations. Hopefully, new generations of devices with improved material and stent design will minimize EVAR complications while providing increased indications for use and durability.

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Conclusion 

In this series, mortality for elective late EVAR AAA-related conversion is not significantly different than primary open repair but is technically more challenging. Endovascular surveillance may identify late complications that require removal and justifies continued monitoring. Early elective conversion of EVAR for type I and type III endoleak or migration that cannot be treated with endovascular procedures may improve outcomes. All patients presenting with rupture in our series had either type I or type III endoleak or migration, and as with open repair, the mortality rate for conversion in the setting of rupture or infection remains very high.

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Author contributions 


Conception and design: RK, SL, ME, RG, DC

Analysis and interpretation: RK, SL, BB

Data collection: SL, BB, RK

Writing the article: RK, SL

Critical revision of the article: RK, SL, BB, ME, RG, DC

Final approval of the article: RK, SL, BB, ME, RG, DC

Statistical analysis: RK, SL

Obtained funding: Not applicable

Overall responsibility: SL

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References 

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 Competition of interest: Dr Lyden is a speaker for Medtronic and Cook Inc, and receives consulting fees from Cook Inc. Dr Greenberg receives funding from Cook Inc for consulting, intellectual property, and travel expenses, and research funding from Cook Inc, Boston Scientific, W. L. Gore, and Cordis. Dr Greenberg receives funding from Cook Inc for consulting, intellectual property, and travel expenses. Dr Clair is a speaker for Cook and W.L. Gore, a consultant for Cordis, and an advisory board member for Medtronic and Boston Scientific.

PII: S0741-5214(08)01789-8

doi:10.1016/j.jvs.2008.10.020

Journal of Vascular Surgery
Volume 49, Issue 3 , Pages 589-595, March 2009

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