Journal of Vascular Surgery
Volume 45, Issue 5 , Pages 885-890, May 2007

Five-year report of a multicenter controlled clinical trial of open versus endovascular treatment of abdominal aortic aneurysms

  • Brian G. Peterson, MD

      Affiliations

    • Saint Louis University, St. Louis, Mo
    • ,
  • Jon S. Matsumura, MD

      Affiliations

    • Northwestern University, Chicago, Ill
    • Corresponding Author InformationReprint requests: Jon S. Matsumura, MD, Department of Surgery, Northwestern University Feinberg School of Medicine, Suite 10-105, 251 E. Huron St, Chicago, IL 60611.
    • ,
  • David C. Brewster, MD

      Affiliations

    • Massachusetts General Hospital, Boston, Mass
    • ,
  • Michel S. Makaroun, MD

      Affiliations

    • University of Pittsburgh, Pittsburgh, Pa
    • ,
  • Excluder Bifurcated Endoprosthesis Investigators

Received 12 July 2006; accepted 8 January 2007. published online 31 March 2007.

Article Outline

Objective

Compare long-term results of endovascular treatment and standard open repair of abdominal aortic aneurysms in a multicenter, concurrent-controlled trial.

Methods

334 subjects were treated with standard open repair (control, n = 99) or the original EXCLUDER Bifurcated Endoprosthesis (test, n = 235). Five-year clinical evaluations and corelab radiographic results are analyzed.

Results

Overall and aneurysm-related survival are similar. There have been ten open conversions, most frequently for enlarging sacs without endoleak. Two patients died after conversion. Including reinterventions and complications of reinterventions as adverse events, there is significant, persistent long-term reduction in major adverse events. At 5 years, corelab reported 0% limb narrowing, 0% trunk migration, 0% component (contralateral leg, aortic extender, and iliac extender) migration, 0% fracture, endoleak in 3% (2 type II/68), and aneurysm growth (>5 mm compared to baseline) in 38% (30/78) of the test group. There are no aneurysm ruptures in either test or control group.

Conclusions

After 5 years follow-up, endovascular repair is a safer and effective treatment compared with open surgical repair for abdominal aortic aneurysms. Major adverse events are less frequent with the endograft despite the need for late reinterventions. Aneurysm expansion is observed in nearly two-fifths of patients but is not associated with endoleak or aneurysm rupture. Multicenter clinical trials are evaluating a newer version of this device designed to avoid this high rate of sac expansion.

 

Since the report of endovascular abdominal aortic aneurysm repair (EVAR) appeared in 1991 by Parodi et al,1 several endoluminal devices designed to treat abdominal aortic aneurysms (AAA) have been developed. Evaluating the safety and efficacy of these devices continues in randomized trials2, 3 and nonrandomized trials.4, 5, 6, 7, 8 In 1997, a feasibility study was undertaken to evaluate the safety, the accuracy of placement, and the reliability of deployment of the original EXCLUDER Bifurcated Endoprosthesis (WL Gore & Associates; Flagstaff, Ariz) for the treatment of AAA. The results of this investigation have previously been reported elsewhere.9 This original investigation was followed a year later by a pivotal nonrandomized controlled clinical trial with the objectives to evaluate the safety of EVAR compared with open surgical repair and the effectiveness of EVAR to exclude the AAA from the blood circulation with the intent to prevent aneurysm related death. Two-year interim results have been published,10 and this study presents the 5-year long-term outcomes.

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Methods 

The trial design has been previously published in detail.10 Briefly, enrollment in this multicenter, concurrent-controlled trial occurred from December 1998 to January 2000, at 19 institutions across the United States. Institutional review board approval was obtained at each site. Devices were deployed in accordance with the labeled instructions for use.

Follow-up 

Patients were seen in follow-up at 1, 6, and 12 months postprocedure, and yearly thereafter. Both test and control subjects were followed for 5 years. Importantly, subjects were not discharged from the study routinely after conversion or explantation. At the time of the follow-up visits, patients received a physical examination, endovascular protocol CT scan, and four-view plain radiographs (in test subjects only). Each institution’s principle investigator was responsible for submission of clinical data, and a core laboratory reviewed all radiographic studies independently. Corelab interpretation is being reported because it has uniform methodology across sites. Clinical evaluations are included regardless of whether corelab data is available for a visit interval. The device-specific radiographic characteristics that were evaluated by the corelab included evidence of limb narrowing, trunk, contralateral leg, aortic extender, and iliac extender component migration, stent fracture, endoleak, and aneurysm size change. Trunk or extender migration was considered significant if it was associated with another complication (ie, endoleak or major adverse event), or moved by ≥10 mm from the initial postoperative imaging modalities. Aneurysm size change was calculated by comparing the maximum aneurysm diameter at each follow-up visit to the baseline. The baseline measurement was taken from the first postoperative imaging. Aneurysm growth by ≥5 mm compared to the baseline measurement was considered significant.

Prior to final data cut-off, there were 128 eligible test patients entering the 5-year interval. Of these 128 test patients, 14 withdrew from the study in the final year, and 3 missed the follow-up visit in the 5-year window. This left 111 test patients available for follow-up in the 5-year window. Of these 111 test patients, 102 had CT scans. Corelab was unable to assess for specific radiographic parameters such as endoleak or migration when there were limitations of imaging (ie, no pre- and postcontrast imaging may compromise the ability to assess for endoleak or lack of paired thin slice reconstructions may preclude accurate assessment of migration). This results in a slightly different denominator of assessable subjects for each corelab parameter.

Adverse events 

Adverse events were defined in accordance with the definitions previously published by Sacks et al11 and are categorized as follows: major adverse events (MAE)- (1) requires therapy and short hospitalization (24 to 48 hours), (2) requires major therapy, unplanned increase in level of care, or prolonged hospitalization (>48 hours), (3) requires permanent adverse sequelae, or (4) requires death. Furthermore, specifically included as MAE are any reinterventions (including conversions) after EVAR and any complications of reinterventions. Aneurysm-related death was defined as death during the same hospitalization or within 30 days of the initial procedure or any reintervention, or death related to the aneurysm or device. By this definition, aneurysm-related mortality includes deaths that are the result of complications after conversion to an open procedure.

Statistical analysis 

The final cut-off for the collection of the 5-year data including clinical evaluations and corelab radiographic results occurred on August 7, 2006. Results are reported as mean ± standard deviation where appropriate; log-rank tests are used to compare overall survival, aneurysm-related survival, and freedom from any MAE throughout follow-up. P values ≤.05 were considered statistically significant. The time-related accumulation of major adverse events within each treatment group was estimated by the Nelson nonparametric method.12 The mean cumulative function (MCF) is a nonparametric estimate of the mean number of major adverse events experienced by subjects over time. Similar to the Kaplan-Meier estimates, the MCF estimation accounts for censoring (including drop out and lost-to-follow-up) of subjects. Graphically, this population mean curve is a step function with many small steps, one for each event in the population. The plots shown in Fig 1 and Fig 2 were created using the Reliability Procedure in the SAS/QC software of SAS Institute (SAS Institute, Inc., Cary, NC). There is no omnibus statistical test for comparing MCF curves, and exploratory 95% confidence limits are plotted at 1 month, 6 months, and annual intervals.

  • View full-size image.
  • Fig 1. 

    Curves show the time-related accumulation of major adverse events (MAE) within the control (dashed) and test (solid) groups estimated by the Nelson nonparametric method. Through the 60-month follow-up period, the total mean cumulative MAE for control subjects was 3.2 events/subject compared with test subjects with 2.4 events/subject.

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Results 

Patient demographics 

Three hundred thirty-four patients were included in this study and underwent either standard open repair of AAA (n = 99; control group) or EVAR (n = 235; test group). Baseline demographics, physical characteristics, laboratory values, and anatomic variables have been previously detailed,10 and there were few significant differences, including: test group had a higher percentage of male subjects, had mean age that was 3 years greater, had higher mean blood urea nitrogen and serum creatinine levels, and had a higher percentage of subjects with hyperlipidemia.

Overall survival 

As shown in Fig 3, survival is comparable between test and control subjects (at 60 months, the survival rates are 72% test vs 81% control). Over the 60- month follow-up period, the survival difference is not statistically significant (P = .12; log rank test).

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  • Fig 3. 

    Kaplan-Meier curves show overall survival in both control (dashed) and test (solid) groups. Over the 60-month follow-up period, the survival difference is not statistically significant (P = .12). Also shown is the number of patients at risk in each population at annual increments over 5 years.

Review of the primary causes of death throughout the 5-year follow-up period demonstrates that both groups experienced a similar pattern. Subjects died of cardiac, neoplastic, pulmonary, and neurologic causes in decreasing order of frequency in both groups. There were no deaths due to aneurysm rupture.

Aneurysm-related survival 

Freedom from aneurysm-related mortality is shown in Fig 4. Rates for test and control are similar, with four aneurysm-related deaths in the test group and two aneurysm-related deaths in the control group during the first 12 months. Between the 12- and 60-month follow-up, there were two additional aneurysm-related deaths in the test group and no additional aneurysm-related deaths in the control group (at 60 months, the survival rates are 97% test vs 98% control). One of the aneurysm-related deaths in the test group was attributed to aspiration pneumonia, which occurred after open surgical explantation of an infected endoprosthesis. The other death was due to prosthetic valve endocarditis after a surgical conversion for aneurysm expansion. Over the 60-month follow-up period, the aneurysm-related survival difference is not statistically different (P = .8; log rank test).

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  • Fig 4. 

    Curves show percentage of patients in control (dashed) and test (solid) groups free from aneurysm-related mortality. Over the 60-month follow-up period, the aneurysm-related survival difference is not statistically different (P = .8). Also shown is the number of patients at risk in each population at annual increments over 5 years.

Major adverse events 

In contrast to the similarities seen between the two groups in terms of overall and aneurysm-related survival at 5-year follow-up, there is a significant difference in the freedom from MAE seen between the two groups. Fig 5 displays the time-related proportion of subjects that remained free of a major adverse event. At 12 months, test subjects had a higher proportion that remained free of a major adverse event compared with controls (65% test vs 26% control). This safety advantage for the test group is maintained between 12- and 60-month follow-up (at 60 months, the proportion free from MAE are 31% test vs 15% control). Over the 60-month follow-up period, the freedom from major adverse events is significantly greater for the test group compared with control (P < .001; log rank test) and strongly support that EVAR with the test device is safer compared to standard open surgery over the 60-month follow-up period.

  • View full-size image.
  • Fig 5. 

    Curves show percentage of patients in control (dashed) and test (solid) groups free from major adverse events (MAE). Over the 60-month follow-up period, the freedom from MAE is significantly greater for the test group compared with the control group (P < .001). Also shown is the number of patients at risk in each population at annual increments over 5 years.

Included in the calculation of MAE for the test group were reinterventions such as conversion to open surgery and resultant complications. Of the 235 patients in the test group, there were 57 reinterventions, including 33 (58%) embolization procedures and 10 surgical conversions. The Table shows the incidence of reinterventions, which are more frequent in the first 2 years after implantation. In one patient who had undergone several previous angiograms and coil embolization procedures, there was evidence of an aorto-enteric fistula seen at the 49-month follow-up leading to open conversion for infected endoprosthesis (previously described). There were two conversions (at 28 and 52 months postprocedure) secondary to aneurysm sac enlargement associated with endoleak. Seven patients underwent conversion to open procedure (range 24 to 62 months postprocedure) for aneurysm sac enlargement without evidence of endoleak.

Table. Reinterventions table for test subjects listing the number of subjects available for evaluation at each time point along with the number of reinterventions and number of subjects undergoing reinterventions at each time point
Report Detailed and/or summarized report6 Months12 Months24 Months36 Months48 Months60 Months
Subjects available for evaluation230221213185161128
Subjects with any reintervention10(4.3%)8(3.6%)16(7.5%)3(1.6%)7(4.3%)3(2.3%)
Total number of reinterventions10817383

In the 5-year corelab evaluation of patients undergoing EVAR there is 0% limb narrowing (0/77), 0% stent fracture (0/74), 0% component (contralateral leg, aortic extender, or iliac extender) migration (0/75), 0% trunk migration (0/70), and 3% endoleak (2 type II/68). No patient had migration, type I or type III endoleak reported by corelab or sites at 5 years in this study, but with larger datasets, rare events are likely to be identified. After 5 years, 32 patients (41%) were noted to have stable aneurysms in terms of size, 16 patients (21%) were noted to have a decrease in aneurysm size, and 30 patients (38%) were noted to experience aneurysm sac enlargement.

Of the 30 patients with sac enlargement at 60 months, three patients were noted previously to have had type II endoleaks at some point during follow-up, two had endoleaks of indeterminate source, 22 patients had no endoleak, and three were not assessed by corelab for endoleak. These 30 patients have had 11 reinterventions: 10 coil embolizations and one ligation of the inferior mesenteric artery. The mean aneurysm diameter of these 30 patients is 6.8cm at 5 years. None of these patients have developed device or component migration, or clinical sequelae of hemorrhagic or nonhemorrhagic rupture.

Cumulative adverse effects 

As many subjects suffer more than one MAE, analysis of cumulative MAE is enlightening. Fig 1 displays characteristics of cumulative major adverse events over the 60-month follow-up for test and control groups. The control group accumulates major adverse events more quickly during the first month. After the first month, the two treatment groups maintain a similar pattern in the mean cumulative major adverse event rates, with the mean consistently higher for the control group over the 60-month follow-up period. Through 1 year, the total mean cumulative events for test subjects was 0.8 events/subject compared with controls with 1.9 events/subject. Through 60 months, the total mean cumulative events for test subjects was 2.4 events/subject compared with controls with 3.2 events/subject.

The MCF difference of MAE between test and control groups is depicted in Fig 2. The graph illustrates the persistent difference in cumulative MAE between the two groups. Ninety-five percent confidence limits widen over time as the sample size decreases. The MCF difference curve permits assessment of the impact of later complications and reinterventions over 5 years compared with the initial differences between test and control groups.

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Discussion 

Numerous endovascular devices have been evaluated for treatment of abdominal aortic aneurysms, and each possesses unique characteristics. EVAR with most of these devices has shown improved short-term results in perioperative morbidity and mortality when compared with open surgical repair, but there are concerns about whether these benefits will persist in the long term because of the higher reintervention rates with EVAR. In the previously published report, striking short-term advantages of EVAR over open surgical repair of AAA was apparent.10 This study demonstrated decreased blood loss, fewer homologous transfusions, and shorter length of stay in comparison to the control group. Early MAE were markedly reduced in the test group (14% vs 57%), and this difference persisted at 2-year follow-up. There was no difference in survival between the two groups at 2 years. A concern was that reinterventions may result in loss of these early benefits of EVAR. The current study follows these same patients out to 5 years postprocedure and demonstrates persistent benefit of reduced MAE with EVAR compared with standard open repair of AAA. It also demonstrates a similar overall survival and aneurysm-related survival, although the study was not powered to evaluate survival differences.

Other limitations of this study include the nonrandomized design and relatively small sample size of patients who had 5-year corelab imaging follow up. The nonrandomized design of the trial may have led to a different risk profile as suggested by significant pretreatment differences previously reported, including mean age 3 years greater, higher mean blood urea nitrogen, higher mean serum creatinine, and anatomic differences necessary for EVAR in the test cohort compared with control group.10 During the course of 5 years, many subjects withdrew from the study, died, or were otherwise lost to follow-up. The smaller sample size of subjects with corelab data did not identify any aneurysm rupture, type I or III endoleak, fracture, or migration; and larger datasets such as in postapproval studies are being gathered to determine the incidence of these rare events.

After 5 years follow-up, there were ten conversions to open procedures in the test group (4.3% of the original test cohort). The reasons for conversion are interesting. Included in these conversions were two patients with endoleaks and aneurysm sac enlargement seen at 28 and 52 months postprocedure. There were seven additional patients who underwent open conversion between 24 and 62 months post-EVAR for aneurysm sac enlargement without demonstrable endoleak. The final conversion was in a patient who had undergone selective catheterization of the superior mesenteric artery and inferior mesenteric artery (IMA) collaterals with embolization who was noted to have persistent endoleak 1 year later necessitating another embolization for progressive enlargement of the aneurysm. At 36-month follow-up, this patient was noted to have developed another type II endoleak of unknown origin and had growth in the aneurysm, and this was followed. At 48-month follow-up, the endoleak had resolved and the aneurysm sac was smaller, but on imaging air was noted in the aneurysm sac indicating possible stent-graft infection. Therefore, this patient underwent open surgical conversion with graft removal and died after complications following the open conversion. This series of conversions from 24 to 62 months postprocedure emphasizes the need for continued surveillance beyond 2 years and opportunities for device improvements.

Not only is continued surveillance important for determining the need for open conversion, but it is also important in determining if reintervention using endovascular techniques is needed. Significant aneurysm growth, defined as diameter increase of ≥5 mm compared to baseline, was seen in 38% of patients in the test group at 5 years. Of note, there were no aneurysm ruptures in this group, but 11 reinterventions were done in these subjects throughout the 5-year follow-up period. Ten of these reinterventions included coil embolization procedures, and there was one patient who underwent ligation of the IMA. Including these reinterventions as MAE, the test group still experienced an advantage of freedom from any MAE in comparison to the control group.

Despite aneurysm sac enlargement in almost two-fifths of the test population, it is noteworthy that there were no aneurysm ruptures. While there has been concern that morphology changes of the aneurysm neck with sac growth may adversely affect the stability and adequacy of the stent-graft in excluding the aneurysm from the native circulation, this was not evident at 5-year follow-up after EVAR. Other reports concur that neck fixation is stable with endotension with three different endograft devices.13 No new type I endoleaks were seen in a detailed analysis of neck apposition by 3-D CT reconstruction in patients treated with this device with midterm sac growth by site or corelab interpretation, including a patient with an initially poor neck and a patient with decreasing apposition distance.14 In a detailed study of a cohort of conversions from five different trials of similar devices, one patient had an initial type I endoleak related to severe 90 degree neck angulation and another patient who developed a paravisceral aneurysm had the endograft removed during the open thoracoabdominal repair.15 There were no other type I endoleak or fixation concerns. Taken together, these studies and the corelab data reported here suggest that late type I endoleak rarely, if ever, results from sac growth. Nonetheless, it is prudent to follow neck apposition length as it may shorten and potentially lead to loss of seal.

It is interesting that 22 of the 30 patients who experienced aneurysm sac enlargement had no demonstrable endoleak throughout the 60-month follow-up. This was initially a perplexing issue for the treating physician and has been addressed with continued observation, laparoscopic or open aneurysm sac decompression, endograft relining, and open conversion.16, 17, 18 While intervention is technically possible, we caution that it may not be necessary in most instances, as the clinical significance of aneurysm sac enlargement without endoleak could be non-hemorrhagic rupture.13, 19 Conversion to open procedure in patients with aneurysm enlargement after EVAR has been shown to be a hazardous procedure.20 While most treating physicians believe that patients experiencing aneurysm enlargement in the setting of persistent endoleak may be candidates for reintervention, the need for these secondary procedures in patients without endoleak is unclear. No concrete scientific evidence exists to guide management of these patients. Clearly, almost all ruptures following EVAR have occurred in the setting of known or acute endoleak.21, 22 These data show that the 30 aneurysms that expand without evidence of endoleak did not rupture over 5 years.

Various mechanisms have been speculated for aneurysm sac enlargement without endoleak and include inability to detect the presence of small endoleaks using conventional imaging modalities, inadequate seal zones that results in thrombus being in contact with the native circulation, and ultrafiltration through the graft material.14, 17, 18, 23, 24, 25, 26, 27, 28 However, based on explant analysis, information gathered from surgical conversion procedures, and in vitro animal studies,15, 29, 30 the movement of serum and fibrin components through the ePTFE graft material used in this device is the predominant contributing factor to the fluid accumulation. It is not clear why this phenomenon occurs in only a minority of patients. The graft composition has been modified to stop ultrafiltration, and another multicenter trial will assess the clinical result of eliminating transmural movement of serous fluid through the device and aneurysm sac growth. A preliminary two-center study suggests that at 12 months, the graft modification has vastly reduced the rate of aneurysm dilatation.31

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Summary 

Five year results of this controlled trial demonstrate that EVAR has fewer major adverse events compared with open repair. Overall and aneurysm-related survival between the two groups is not different. Aneurysm sac growth due to transgraft ultrafiltration occurs frequently with the original device design and has been addressed with subsequent graft modification.

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Author contributions 


Conception and design: BP, JM, DB, MM

Analysis and interpretation: BP, JM

Data collection: BP, JM

Writing the article: BP, JM

Critical revision of the article: BP, JM, DB, MM

Final approval of the article: BP, JM, DB, MM

Statistical analysis: JM

Obtained funding: JM

Overall responsibility: JM

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References 

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  29. Trocciola SM, Dayal R, Chaer RA, Lin SC, DeRubertis B, Ryer EJ, et al. The development of endotension is associated with increased transmission of pressure and serous components in porous expanded polytetrafluoroethylene stent-grafts: characterization using a canine model. J Vasc Surg. 2006;43:109–116
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 Competition of interest: Dr Matsumura has been a paid consultant, clinical investigator, and/or received support from Abbott, Bard, Cook, Cordis, ev3, Medtronic, and WL Gore.

PII: S0741-5214(07)00060-2

doi:10.1016/j.jvs.2007.01.044

Journal of Vascular Surgery
Volume 45, Issue 5 , Pages 885-890, May 2007

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