UBC Faculty Research and Publications

Endovascular graft treatment of infrarenal aortic aneurysms Bassett, Kenneth, 1952-; Morris, Veronica; Chambers, Keith; Fry, Peter; Foerster, Victoria; Fatin, Neil Jun 30, 1998

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Centre for Health Servicesand Policy ResearchENDOVASCULAR GRAFTTREATMENT OF INFRARENALAORTIC ANEURYSMSBCOHTA 98:5J        JUNE 1998British Columbia Office of Health Technology AssessmentJoint Health Technology Assessment SeriesU N I V E R S I T Y  O F  B R I T I S H  C O L U M B I AEndovascular graft treatment of infrarenal aortic aneurysmsKen  Bassett, MD PhDSenior Medical Consultant, BC Office of Health Technology AssessmentAssociate Professor, Department of Family Practice, University of British ColumbiaVeronica Morris, RN BSc MPAManager Research and Accreditation, Capital Health Region, VictoriaKeith Chambers, MD CCFP MHScAssistant Director, Centre for Clinical Epidemiology and EvaluationVancouver Hospital and Health Sciences CentrePeter Fry, MD FRCSClinical Professor, Department of Surgery, University of British ColumbiaVictoria Foerster, MD MScMedical Consultant, Acute and Continuing Care DivisionMinistry of Health and Ministry Responsible for SeniorsNeil Fatin, MB BS FRACP MBA FRACMAMedical Consultant, Provincial Programs, Acute and Continuing Care DivisionMinistry of Health and Ministry Responsible for SeniorsEndovascular graft treatment of infrarenal aortic aneurysms 1BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTTable of ContentsINTRODUCTION TO THE SERIES 21.0  INTRODUCTION 32.0  CLINICAL BACKGROUND 33.0  TECHNOLOGY BACKGROUND 44.0  ASSESSMENT OF CLINICAL RESEARCH 64.1  Standards of evidence 64.2  Methods 65.0  DISCUSSION 126.0  CONCLUSIONS 13Endovascular graft treatment of infrarenal aortic aneurysms 2BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTIntroduction to the SeriesThe Joint Heath Technology Assessment Series reports on projects initiated bythe British Columbia Office of Health Technology Assessment (BCOHTA) andevidence-based medicine programs in BC. These programs are dedicated toproducing unbiased, systematic reviews of clinical efficacy and effectivenessevidence for health care providers, administrators, policy makers, and thegeneral public, and currently include:· Therapeutics Initiative (TI), Department of Pharmacology and Therapeutics,Faculty of Medicine, University of BC, Vancouver· Technology Assessment Committee, Capital Health Region, Victoria· Drug Benefit Committee, Pharmacare, and ad hoc Health TechnologyAssessment Committees, the Ministry of Health and Ministry Responsible forSeniors, Victoria· Technology Assessment Committee, Workers' Compensation Board of BC,Richmond· Population Testing Programs, Boundary Health Unit, South Fraser HealthUnit, Surrey· BC Research Institute for Child and Family Health, BC Women’s andChildren’s Hospital, Vancouver· Public Health Nursing, Boundary Health Unit, South Fraser Health Region,Surrey·    Centre for Clinical Epidemiology and Evaluation, Vancouver Hospital andHealth Sciences Centre, VancouverTopics reflect initiative and institutional needs. Priority is given to topics withsignificant impact on patient health and health care costs, and with issues inmore than one context. The goal is to teach systematic review and criticalappraisal skills and coordinate efforts among geographically separate andinstitutionally diverse contexts.Two different types of evidence-based medicine problems are addressed:1. uncertainty regarding new technology2. discrepancy between evidence and practice for established technology.The Joint HTA Series will produce scientifically valid systematic reviews that keyindividuals in each receptor site support. The key individuals are needed topresent and defend the systematic review conclusions during ongoing committeedebates. This step is essential to connect health policy, including fundingdecisions, to the available efficacy and effectiveness evidence.Endovascular graft treatment of infrarenal aortic aneurysms 3BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENT1.0 IntroductionEndovascular graft (EVG) treatment whereby a graft is inserted through the femoral arteryto repair nfrarenal abdominal aortic aneurysm (AAA) has potential advantages forpatients and the health care system. Patients may avoid the significant morbidity andmortality associated with current major abdominal surgery techniques utilized in thetreatment of AAA. The health care system may benefit from saving operating roomresources and reduced hospital utilization because this procedure requires less intra-operative and post-operative time.Cardiovascular surgeons at the Vancouver Hospital and Health Sciences Centre and inVictoria have requested funding for this procedure. The Vancouver Hospital requestasked the Acute and Continuing Care Division of the BC Ministry of Health to fund EVGplacement in patients with AAA that have a high incidence of fatal rupture, who areconsidered too frail for open abdominal resection and have no other treatment option. TheBC Ministry of Health agreed, on compassionate grounds, to fund 18 EVGs (not includindout of province cases) in inoperable patients with life-threatening aneurysms.The cardiovascular surgeons and radiologists working in the Capital Health Region inVictoria, in contrast to the initial request to the BC Ministry of Health, asked for a moregeneral application of EVGs beyond otherwise inoperable patients. The doctors in theCapital Health Region proposed EVGs as a substitute for open abdominal resection forpatients considered suitable for this procedure.2.0 Clinical backgroundAbdominal aortic aneurysm (AAA), along with coronary and cerebral artery occlusion, isone of the more severe features of arteri sclerotic vascular disease.1 AAAs are the mostfrequent form of aneurysm. AAAs are most often located between the ostiums of the renalarteries and the aortic bifurcation. Most AAAs occur in men during the 6th or 7thdecades.2,3 The most common symptom is back pain, although two-thirds of AAAs remainasymptomatic. AAA rupture is frequently the cause of death.4 Intra-operative mortalityincreases dramatically if rupture has occurred pre-operatively.5 Patients at greatest risk ofrupture also have the greatest operative risk due to extensive co-morbidity.6Symptomatic and large (>5cm) AAAs have been successfully treated, since the early1950s with resection of the affected aortic segment and replacement with a syntheticprosthesis.7 Operative morbidity and mortality rates (3-7% or higher, depending on patientselection and surgical expertise) while generally declining, vary markedly among treatmentcentres, depending greatly on patient inclusion and exclusion criteria.5p.807The treatment of AAAs smaller than 4-5cm remains controversial. Proponents of surgicalrepair argue that early treatment avoids the increased morbidity and mortality due to AAAenlargement and patient demise. Critics argue that surgical risk outweighs the risk of AAArupture because little is known about whether the smaller AAAs will continue to enlargeor will ultimately need resection.Endovascular graft treatment of infrarenal aortic aneurysms 4BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENT3.0 Technology backgroundEndovascular repair of AAAs reflects developments in both endovascular prostheses andimaging technology.Endovascular prostheses consist of two elements:1) a self-expanding or balloon-expandable stent, made from stainless steel or other alloys(i.e. Nitinol, a nickel titanium alloy). The stent portion is designed to maintain patencyof the affected vessel and to keep the graft in place. The self-expanding tents retaintheir arterial location using radial force while the balloon-expandable st nts usually usesome form of fixation pins or hooks2) a variety of woven and knitted fabrics (i.e. Dacron) grafts. Each fabric varies inimportant properties such as degree of tissue incorporation, elasticity, stability, andsize.EVGs have several technical requirements as summarized in a recent review article byGreen et al:An endoprosthesis must adhere securely to the atherosclerotic aortic cuff. Anymovement could compromise the renal or iliac artery orifices or result in a para-prosthetic leak. The prosthesis must also be secured distally in the aortic or iliacartery wall.8p.102Basic science studies have not reported on the long term interaction between blood, graft,stent and vessel wall.8p.106These fabric/stent EVG combinations are loaded into delivery systems of relatively smalldiameter. The more recent delivery system involves a wire introduce  over which the graftis inserted and positioned.The EVGs and their delivery systems have evolved rapidly from initial straight graphs tobifurcated grafts, inserted using bilateral femoral access. The advantages of a bifurcatedgraft are that it “allows the common channel to be very short, reduces the need for precisemeasurements of aneurysm length, and ensures adequate fixation of the distalcomponents.”8p.103The addition of bifurcated grafts provides an important technical advantage over straightgrafts because the two distal arms, which fit within the iliac arteries, help to secure thegraft both proximally and distally. The second arm of the graft is placed by obtainingaccess through the contra-lateral iliac artery. Most case series, some of which are reportedbelow, state that bifurcated grafts have increased the percentage of operable patients,particularly patients with a short proximal aortic cuff. Bifurcated grafts are thepredominant technology under evaluation.Along with rapid changes in graft technology have been equally rapid changes in imagingtechnology. Digital fluroscopic technology is needed not only to assess the size and shapeEndovascular graft treatment of infrarenal aortic aneurysms 5BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTof the AAA prior to surgery, but also in the operating room to monitor placement of theprosthesis, and to assess patency and leakage.Anatomical information is gathered on each aneurysm using aortography:The length and diameter of each cuff, the length of the aneurysm, the tort osity,size, and morphology of the iliac arteries, the location of the renal arteries and thesignificance of the inferior mesenteric artery must be determined in every case.This will require specialized imaging with three-dimensional reconstructions oreither computed omography or magnetic resonance imaging data andaortography.8p.102Cooperation is essential between radiologists and cardiovascular surgeons during the EVGplacement procedures.No straight or bifurcated EVGs have received approval by the US Food and DrugAdministration (FDA). Therefore, EVGs used to date at the Vancouver Hospital do notreflect regulatory approval in the US. A consultant at the Canadian Health ProtectionBranch (HPB) recently explained that the EVGs used in Vancouver represent virtually allof the EVGs use to repair AAA in Canada to date.The US FDA has approved Phase I and II studies9 of on  EVG, known as the “Talentgraft” manufactured in the US.10 This EVG graft and delivery system, which is used inVancouver, has been described in detail11,12 and received regulatory approval forcommercial release by Europeon authorities.A Phase II trial comparing EVG with conventional repair is described by Moore et al:During the Phase II portion of the study, a total of 15 centers will randomlyallocate patients with abdominal aortic aneurysms, suitable for EGS [EVG]implantation, to either conventional operation or ndovascular graft repair. Theobjective of the Phase II portion of the study will be to compare the 12 monthmorbidity, mortality, and cost between the experimental and control groups.10p.338Some early results of the Phase II trial are reported from one centre.13Endovascular graft treatment of infrarenal aortic aneurysms 6BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENT4.0 Assessment of clinical research4.1 Standards of evidenceThe individuals appraising the evidence at CHR, BC Ministry of Health, CCEE andBCOHTA all agree on the following standards of evidence for assessment of EVG :1) The burden of proof of patient benefit rests with the proponents of the EVGtreatment. 2) EVG treatment can only be considered in the context of institutions with operatingrooms with state-of-the-art imaging technology. 3) The effectiveness of EVG treatment of AAA should be scientifically proven wherefeasible in a randomized control trial. The necessary duration of patient assessmentremains controversial. One group of authors recommends a minimum two-yearassessment period,14 while other authors recommend a minimum five-year period.15The latter authors argue that a five-year period is necessary to determine the relativerate of aneurysm rupture. The two-year period seems reasonable at this early stage oftechnology development. 4) The circumstances in which evidence from a study other than a randomized controltrial may be acceptable is in the case of surgically inoperable patients with largeaneurysms known to have a high incidence of rupture. In these instances alternativestudy designs may be useful to compare the new technique with a historical controlgroup or some other comparison group. 5) Case series, while important to establish feasibility and safety, do not provide efficacyand effectiveness evidence.4.2 MethodsSearch strategyThe National Institute of Health, MEDLINE and European EMBASE databases, weresearched from 1980 to present using the keywords: abdominal aortic aneurysm,endovascular, endograft, stent, endoluminal, transfemoral, endoprosthesis. The CurrentContents database was searched to December 1997. The Cochrane Library was searchedfrom 1993 to 1997.The reference lists from retrieved articles were scanned to identify additional trials. Nodata was obtained directly from device manufacturers.A fugitive literature search was conducted to identify the published and unpublishedscientific literature that does not appear in peer-reviewed journals or that is not indexed inthe more widely used commercially available databases. A comprehensive search was alsoEndovascular graft treatment of infrarenal aortic aneurysms 7BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTperformed on all health technology assessment publication lists to verify the existence ofsimilar reports.Inclusion/exclusion criteriaThe primary search was for randomized controlled trials comparing EVG with openabdominal repair. Because randomized controlled trials have not been conducted, clinicalevidence obtained from non-randomized study designs was included if it met the followingcriteria:· prospective· reasonable number of patients· explicit process for patient selection and assessment, and· technology similar to what is being considered in BCReview articles were also included to establish background understanding of EVGtechnology. In addition, selected articles that present the epidemiology and natural historyof AAA were included.This review excluded literature reporting on the relative merits of various pre and postoperative imaging technologies.Search findingsNo published randomized or non-randomized, contolled trials have compared EVG withopen abdominal resection of AAA.One published case series by White et al (1996)15 compared patients treated withendovascular grafts with historical controls.Reports from three prospective case series are appraised below. White et al15 is includ dbecause it compares EVG with an, albeit historical, control group. Moore et al16 is ch s nbecause it is the report from the Phase I trial sanctioned by the FDA, the most relevantregulatory body to Canada, and it uses the EVG technology currently in use in BC. Blumet al17 was chosen because, although the trial uses a different form of EVG technologythan that currently approved by the FDA for clinical trials in the US, it does use the EVGtechnology promoted for purchase in the Capital Health Region. The third study also isone of the largest and has one of the longest post operative patient assessments to date.Endovascular graft treatment of infrarenal aortic aneurysms 8BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTSeveral case series without historical controls have been published throughout the world.*The following articles were retrieved, but not appraised:Australia15,18,19USA11,12,13,16Germany and Austria17United Kingdom20France14Netherlands21Multinational case series are also reported.20,22 Individual patient case histories are alsocommon, particularly describing adverse events.23Critical appraisalThe three case series15,16,17 were critically appraised by four different assessers at the BCMinistry of Health, the Capital Health Region, the Centre for Clinical Epidemiology andEvaluation, and BCOHTA by using the methodology of Schechter and Leblanc.241)  White et al (1996)15White et al compared 27 patients receiving straight and bifurcated endovascular grafts to28 matched historical controls. The authors did not consider the study as definitive.Rather, they compared the two populations in order to judge whether a randomized trialwas ethical and feasible.PopulationPatient selection, although described as sequential, is extremely problematic. The authorseliminated patients from both groups considered unsuitable for open surgical resection orEVG repair, respectively. The primary analysis also excluded the six EVG patients whorequired immediate conversion to open repair. Excluding these patients, as the authorsnote, biases results in favour of the EVG population.DesignThe study was designed to compare immediate surgical and post surgical complications,safety, and resource utilization. The duration of patient assessment was not stated, butseems very short. For example, it does not include mortality rates at 30 days.DeviceThree graft systems were used: the EVT Endograft (8 patients; 7 straight, 1 bifurcated),the White-Yu endoluminal graft system (19 patients; 14 straight, 4 bifurcated), the Chuterbifurcated graft (1 patient).                                         * Note: the majority of case series were not retrieved.Endovascular graft treatment of infrarenal aortic aneurysms 9BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTStudy findingsA strength of the report is that it includes details on individual patients, both operative andimmediate post-operative complications:mortality rate EVG = 0 Open = 1vascular complicationsEVG = 25% Open = 15%systemic complicationsEVG = 29% Open = 37%mean duration of operation EVG = Openincidence of remote/systemic complicationsEVG = Openlength of hospital stay EVG = Openblood loss EVG < OpenKey appraisal issuesBias is likely due to open selection of historical controls. The study did not report onpatient outcome after hospital discharge. No analysis of different EVG systems wasconducted.Study conclusionRCT is needed and seems feasible.Appraisal conclusionThe comparison is invalidated by patient selection bias and limited outcome measures. Thetrial provides no information on which version of a particular graft technology to use inthe subsequent trial.2)  Moore et al (1996)16The authors describe this as a feasibility, Phase I trial of straight tube grafts. The FDAestablished the necessary study design features and dictated which technology could beused. Partial reports of the same study population were published earlier.11,12,13Note: multiple publications based on the same patient population are common.PopulationA total of 46 patients, in 13 US centres were considered suitable for an EVG procedure.In particular, all patients met the most limiting inclusion criteria which is that they all hadan infrarenal AAA with at least 2 cm superior and inferior cuffs of non-aneurysmal vessel.Most patients with AAA were excluded. As the study reports:Although screening statistics were not a requirement of the study, one study centredid maintain these data; they reported that it was necessary to screen 69 patients toidentify the 10 who subsequently received tube graft repair. The most commoncause of rejection was the lack of a distal neck.17p.551Endovascular graft treatment of infrarenal aortic aneurysms 10BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTA study from the UK similarly found that only 5 of 44 patients were suitable for straighttube grafting.20DesignThe study was a prospective case series designed to provide descriptive details of patientselection, surgical technique, safety, resource utilization (13 centres were used, someinsertion, only 1 device).DeviceThe EVT graft consists of a self-expanding stent with metallic hook fixation devices thatare seated using a moveable balloon catheter; Dacron fabric. The initial device, called EGSI, malfunctioned causing a halt in the trial until an EGS II device was developed. Theproblem is described as a metallic attachment system failure.Primary end pointsA 30-day mortality data was reported on the entire cohort. The mean follow-up was 14months.Study findings39/46 attempts were successful; conversion to open abdominal resection was not required.Conversions to open abdominal resection were immediate (n=6) and after 4 days (n=1).The following complications were reported in the successful cases:· myocardial infarction = 1· iliofemoral artery injury = 8· minor thromoboembolism = 2· superficial cellulitis = 6· lymphatic lead = 1· postoperative fever = 9In addition, 17/39 patients showed leaks on contrast-enhanced CT scans. Of these, 8/17had persistent leaks, 5/17 underwent repeat percutaneous transluminal balloon angioplasty(successful in 1 patient). 1 needed open repair and 6 continued to leak without subsequentneed of interventions.Key appraisal issuesThe patients were carefully selected as suitable candidates for straight tube graft insertion.This likely explains the relatively high (85%) initial success rate. The carefully selectedpatients from this series cannot be compared with patients considered suitable for eitherstraight or bifurcated EVGs. A much higher percentage of patients with AAA are suitablefor repair with bifurcated EVGs.Endovascular graft treatment of infrarenal aortic aneurysms 11BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTAppraisal conclusionThis study only provides information to the research community and committeesconsidering whether or not, and how to conduct, Phase II trials of this technology. Noefficacy conclusion can be drawn form this study.3)  Blum et al (1997)17Blum et al report the largest case series published to date involving both straight andbifurcated EVGs. The authors, similar to Moore et al17 discussed above, describe theirresearch as a feasibility study.Population154/331 patients with infrarenal AAA (47%) were treated with straight (21/154) andbifurcated grafts (133/154) at three centres in Germany and Austria. Patients wereclassified into one of five categories determined by anatomical features of the AAA.Category A: suitable aortic length for straight EVGCategories B and C:suitable for bifurcated graftCategories D and E:unsuitable, need open repair.DesignThe study was designed as a Phase I trial to provide descriptive details of patient selection,surgical technique, safety, and resource utilization. Angiography and CT scans wereconducted at discharge, 3, 6, 12 and 24 months.DeviceThe graft is “a self expanding endoprosthesis composed of a nitinol frame annealed into atubular zigzag configuration by a 7.0 polypropylene thread and covered with a 0.1mmwoven-polyester fabric.”18p.15Primary end pointsPrimary technical success: “the complete exclusion of the abdominal aortic aneurysm fromthe circulation, with the restoration of normal blood flow.” 18p.15Study findingsPrimary technical success was achieved in 134/154 (87%) of patients.Category A, straight graphs = 18/21 (87%)· 2 patients: proximal· 1 patient: distal leak and dislodgmentCategories B and C, bifurcated graphs = 116/133 (87%)· 3 patients: converted to surgical repair· 1 patient: ruptured iliac artery with delivery device· 2 patients: insertion device could not be advanced· 8 patients: tears in polyester fabric required additional stentsEarly complicationsEndovascular graft treatment of infrarenal aortic aneurysms 12BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTMinor complications included insertion site damage and biochemical changesMajor complications were rupture of iliac artery = 1, embolic graft occlusion requiringamputation of the foot = 1, and acute hepatic failure and death = 1.Late complicationsCategory A, straight graphs: 3 patients required subsequent graphs due to leaks.Categories B and C, bifurcated graphs: no migration, 11 leaks. No open procedures wererequired.Appraisal conclusionFurther research is warranted and Phase II trials seem feasible.5.0 DiscussionThe initial clinical experience described by Parodi et al25 and current EVG use in BCprovide EVG on a compassionate basis to patients with contra-indications to conventionalopen abdominal resection. While much less commonly reported, other authors22 c ntinueto describe some success with EVG use in these highest risk patients. This review,however, concerns the much broader application of EVG technology as a potentialsubstitute to open surgical repair.In the continuum from experimental to state-of-the art, EVG treatment of AAA as asubstitute for open abdominal resection remains at what the US National Institutes ofHealth call the “investigational” stage.26 The investigational stage is defined as the placeon the continuum where: “There is insufficient evidence to determine the safety ofeffectiveness of the technology. Use of the technology in patient populations should beconfined largely to research protocols.”25p.19The investigation stage fits within a set of ordinal categories:· Inception: virtually untested· Innovation: preliminary testing· Investigation: as above· Promising: appropriate for some indications· Established: adequately evaluated· Guidelines: standard careEVG remains in the investigation stage for several reasons:1) EVG technology is in a rapid state of evolution. The technology used for repairs varieswithin studies, between studies, and even changes during studies. 2) Case series describe a wide range of procedural problems including the difficulties ofobtaining access through small or tortuous iliac arteries, obtaining accuratemeasurements of the aneurysm and adjacent arteries, and securing the EVGs bothproximally and distally. The attachment problems are particularly marked for patientsEndovascular graft treatment of infrarenal aortic aneurysms 13BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTwith a relatively short normal aortic cuff proximal to the aneurysm (but distal to therenal artery bifurcation). 3) EVG remains investigational because, while feasible in a few carefully selectedindividuals, the safety, effectiveness, and durability of any EVG system is not yetproven in randomized controlled trials. Most significantly, EVGs have not been shownto have medium and long term reduction in deaths from AAA rupture. The follow-upfor EVG is relative short averaging 14 months in the study by Moore et al16 and 13months in the study by Blum et al.17 Follow-up for conventional studies often exceeds10 years.7 4) Clinical trial methodology, particularly outcome measures, have not becomestandardized. This may change with adoption of the recommendations of recentconsensus conferences.27,28 These conferences recommended standardized methods foranatomical classification of AAAs, a definition of procedural success, and a procedurefor clinical assessment, as well as necessary data collection forms. Other authors29have called for more complete reporting of late as well as early EVG complications.6.0 Conclusions1) Decisions regarding public funding of EVG technology as a replacement for openabdominal resection of AAA must await technology maturity and clinical trial resultsregarding specific EVG technology. 2) The current practice of offering EVG on a compassionate basis to patients withcontra-indications to conventional open abdominal resection should continue understudy conditions. All patients should be offered a chance to enroll in a research studythat is designed to measure the effectiveness of this procedure in this specific group ofpatients. 3) Literature review for further evidence on the effectiveness, indications, and costbenefit of EVG should occur in conjunction with the various stakeholders in this newtherapy.Endovascular graft treatment of infrarenal aortic aneurysms 14BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENTReferences                                         1 Roger VL Ballard DJ, Hallett JW Jr, Osmundson PJ, Puetz P, Gersh BJ.  Influence of coronary arterydisease on morbidity and mortality after abdominal aortic aneurysmectomy: a population-based study,1971-1987. J. Am Coll Cardiol 1989;14:1245-52.2 Collin J, Aradjo L, Walton J, LIndsell D.  Oxford screening pro ramme for abdominal aortic aneurysmsin men aged 65 to 74 years.  Lancet 1988;2:613-5.3 Scott RAP, Ashton HA, Kay DN, Abdominal aortic aneurysm in 4237 screened patients: prevelence,development and management over 6 years.  Br J Surg 1991;78:1122-5.4 Greenhalgh RM.  Prognosis of abdominal aortic aneurysms.  BMJ 1990;301:136.5 Katz DI, Stanley JC, Zelenock GB.  Operative mortality rates for intact and ruptured abdominal aorticaneurysms in Michigan: an eleven year statewide experience. J Vasc Surg 1994;19:804-17.6 Cronenwett JL, Murphy TF, Zelenock GB, et al. Actuarial analysis of variables associated with ruptureof small abdominal aortica aneurysms.  Surgery 1985;98:472-83.7 Ernst CB.  Abdominal aortic aneurysm.  NEJM 1993;328:1167-728 Green RM,  Chuter TAM.  Evolution of technologies in endovascular grafting.  Cardiovascular Surgery1995;3(2):101-107.9 Phase I was designed to test the safety and efficacy of a limited number of implants in patients withAAA. Phase II is a prospective comparison of the results of EVG versus those of conventionaltransabdominal AAA repair.  Phase III is designed to look at the long-term results of EVG repair withrespect to stability and durability of the device and to protect against aneurysm enlargement and rupture.10 EndoVascular Technologies, Inc. (EVT); Menlo Park CA.11 Moore WS,  Vescera CL.  Repair of Abdominal Aortic Aneurysm by Transfemeral Endovascular GraftReplacement.   Annals of  Surgery 1994;220:331-341.12 Naslund TC, Edwards WH Jr, Neuzil DF, Martin RS Snydor SO Jr, Mulherin JL Jr, Failor M,Mcpherson K.  Technical Complications of e dovascular abdominal aortic aneurysm repair. J Vasc Su g1997;26:502-10.13 Edwards, WH Jr,  Naslund TC, Edwards WH Sr, Jenkens JM,  McPherson K.  Endovascular Grafting ofAbdominal Aortic Aneurysms.  A Preliminary Study.  Ann of  Surg 1996;223(5):568-575.14 Aho S, Long A, Pazart L.  Endovascular stent treatment of aortic aneurysms.  Paris: Agence Nationalepour le Development de l’Evaluation Medicale 1995:56.15 White GH,  May J,  McGahan T, Yu W, Waugh RC, Stephen MS, Harris JP.  Historic controlcomparison of outcome for matched groups of patients undergoing endoluminal versus open repair ofabdominal aortic aneurysms.  J Vasc Surg 1996;23:201-12.16 Moore WS, Rutherford RB.  Tansfemoral endovascular repair of abdominal aortic aneurysm: results ofthe North American EVT Phase I trial.  J V scSurg 1996;23:543-53.17 Blum U. et al.  Endoluminal Stent-grafts for infrarenal abdominal aortic aneurysms. NEJM1997;336:13-20.18 May J,  White GH,  Yu W,  Waugh R,  Stephen MS,  Sieunarine K,  Chaufrour X,  Harris JP.Endoluminal repair of abdominal aortic aneurysms: Strengths and weaknesses of various prosthesesobserved in a 4.5-year experience.  J  Endovasc Surg 1997; 4: 147-151.19 May J,  White GH,  Yu W,  Waugh R,  Stephen M,  Harris JP.  Concurrent comparison of endoluminalrepair vs. no treatment for small abdominal aortic aneurysms.  Eur J Va c Endovasc Surg 1997;13: 472-476.20 Andrews SM, Cuming ST, Barrett NK, Greenhalgh RM, Nott DM.  Assessment of feasibility forendovascular prosthetic tube correction of aortic aneurysm.  Br J of  Surg 1995;82:917-19.21 Balm R,  Eikelboom BC,  May J,  Bell PRF,  Swedenborg J,  Collin J. Early experience withtransfemoral endovascular aneurysm management (TEAM) in the treatment of aortic aneurysms.  Eur JVasc Endovasc Surg 1996;11: 214-220.22 Murphy KD,  Richter GM,  Henry M,  Encarnacion CE,  Le VA,  Palmaz JC.  Aortoiliac aneurysms:Management with endovascular stent-graft placement. Rad 1996; 198: 473-480.23 Sandison AJP,  Edmondson RA,  Panayiotopoulos YP,  Reidy JF,  Adam A, Taylor PR.  Fatal colonicischaemia after stent graft for aortic aneurysm.  Eur J Vasc Endovasc Surg 1997; 13:219-220.Endovascular graft treatment of infrarenal aortic aneurysms 15BC OFFICE OF HEALTH TECHNOLOGY ASSESSMENT                                                                                                                   24 Schechter MT,  LeBlanc FE.  Critical Appraisal of Published Research.  In, Hanstroidle W,  Spitzer O,McPeek B, Mulder DS,  McKneally MF, eds.  Principles and practice of research: strategies for surgicalinvestigations.  New York: Springer-Verlag:112-117.25 Parodi JC,  Palmaz JC, Baone HD.  Tansfermoral intraluminal graft inplantation for abdominal aorticaneurysms.  Ann Surg 1994;220:5:491-9.26 Ferguson JH.  Perspective of the National Institutes of Health.  In Grady ML (ed),  Summary Report.New Medical Technology: Experimental or S te-of-the-Art.  US Department of Health and HumanServices. Agency for Health Care Policy and Research.  ACHPR 92-0057, June 1992:19-23.27 Dorros G,  Parodi J,  Schonholz C,  Jaff MR,  Diethrich EB,  White G,   Mialhe C,  Marin ML,  StelterW-J,  White R,  Coppi G,  Bergeron P.   Evaluation of endovascular abdominal aortic aneurysm repair:Anatomical classification, procedural success, clinical assessment, and data collection. J Endovasc Surg1997;4(2): 203-225).28 Harris PL,  Buth J,  Mialhe C,  Myhre HO,  Norgren L,  Allen RC, Fogarty TJ.  The need for clinicaltrials of endovascular abdominal aortic aneurysm stent-graft repair: The EUROSTAR project.  J EndovascSurg 1997; 4: 72-79.29 Geroulakos G,  Lumley JSP,  Wright JG. Factors influencing the long-term results of abdominal aorticaneurysm repair.  Eur J Vasc Endovasc Surg 1997; 13: 3-8.

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