Devices Used for Endovascular Aneurysm
`Repair: Past, Present, and Future
`Benjamin M. Jackson, M.S., M.D.,1 and Jeffrey P. Carpenter, M.D.2
`
`ABSTRACT
`
`Since its first implementation in patients in 1991, endovascular aneurysm repair
`for abdominal aortic aneurysms has gained wide acceptance and availability. This develop-
`ment has been fueled in great part by advances in stent-graft design and by a variety of
`devices for various anatomic features. This commentary will summarize some of these
`endograft developments and indicate the path forward for novel endoprostheses.
`
`KEYWORDS: AAA, endovascular aneurysm repair (EVAR), stent graft, endograft
`
`Objectives: Upon completion of this article, the reader should be able to recall the history of stent-graft development for abdominal
`aortic aneurysms, current devices used in the United States, and upcoming developments and novel endografts.
`Accreditation: Tufts University School of Medicine (TUSM) is accredited by the Accreditation Council for Continuing Medical Education
`to provide continuing medical education for physicians.
`Credit: TUSM designates this educational activity for a maximum of 1 AMA PRA Category 1 CreditTM. Physicians should only claim
`credit commensurate with the extent of their participation in the activity.
`
`Herein we present a review and some commen-
`tary on the current and future state of endovascular
`aneurysm repair (EVAR) devices, for the treatment of
`abdominal aortic aneurysms (AAAs). The discussion
`will commence with a brief review of the history of
`endovascular AAA repair.
`
`PAST
`No history of EVAR may start without mention of Dr.
`Juan Parodi’s elective repair in five patients with AAA in
`19911 using a custom-made Dacron tube endoprosthesis,
`inserted transfemorally, and fixed with balloon-expand-
`able stents. Subsequently, bifurcated endografts were
`described and implanted, initially in 1994.2 And aorto-
`uni-iliac or aorto-uni-femoral grafts, requiring coincident
`occlusion of the contralateral common iliac and femoral-
`
`femoral bypass grafting, were reported in 19973,4; many
`still consider this approach the standard or best for the
`endovascular treatment of ruptured aneurysms.
`Over time, EVAR gained traction for use in
`patients with ruptured aneurysms; this approach was
`initially reported in 1994 by Yusuf et al.5 The modular
`design of current endoprostheses was pioneered by the
`Sydney, Australia group.6
`
`PRESENT
`There are presently five endograft platforms, from four
`companies, which have received U.S. Food and Drug
`Administration (FDA) approval for clinical use. These
`devices, their manufacturers, and their dates of FDA
`approval are listed in Table 1. The largest proximal neck
`treated by each device is listed in Table 2.
`
`1Division of Vascular Surgery and Endovascular Therapy, Department
`of Surgery, Hospital of the University of Pennsylvania, Philadelphia,
`Pennsylvania; 2Department of Surgery, Cooper University Hospital,
`Camden, New Jersey.
`Address for correspondence and reprint requests: Benjamin M.
`Jackson, M.S., M.D., Assistant Professor, Division of Vascular Surgery
`and Endovascular Therapy, Department of Surgery, Hospital of the
`
`University of Pennsylvania, 4 Silverstein Pavilion, 3400 Spruce Street,
`Philadelphia, PA 19104 (e-mail: benjamin.jackson@uphs.upenn.edu).
`Aortic Stent Grafts; Guest Editor, S. William Stavropoulos, M.D.
`Semin Intervent Radiol 2009;26:39–43. Copyright # 2009 by
`Thieme Medical Publishers, Inc., 333 Seventh Avenue, New York,
`NY 10001, USA. Tel: +1(212) 584-4662.
`DOI 10.1055/s-0029-1208382. ISSN 0739-9529.
`
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`40
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`SEMINARS IN INTERVENTIONAL RADIOLOGY/VOLUME 26, NUMBER 1 2009
`
`Table 1 FDA-Approved Devices for EVAR
`
`Device
`
`Manufacturer
`
`Date of Initial
`FDA Approval
`
`Stent
`Material
`
`Graft Material
`
`Delivery System Distinctive Feature
`
`AneuRx
`
`Medtronic
`
`1999
`
`Nitinol
`
`Woven polyester
`
`Integrated sheath No anatomic fixation
`
`AAAdvantage
`
`Excluder
`
`Gore
`
`Zenith Flex
`
`Cook
`
`2002
`
`2003
`
`Nitinol
`
`ePTFE
`
`Separate sheath*
`
`Infrarenal active
`
`(hooks) fixation
`
`Stainless steel
`
`Woven polyester
`
`Integrated sheath Pararenal uncovered
`
`nor pararenal stent
`
`Powerlink
`
`Endologix
`
`2004
`
`Cobalt chromium
`
`ePTFE
`
`Integrated sheath Unibody design
`
`Talent
`
`Medtronic
`
`2008
`
`alloy
`
`Nitinol
`
`Woven polyester
`
`Integrated sheath Pararenal uncovered
`
`stent
`
`*In contrast to the other stent grafts listed, the Gore Excluder is delivered through a separate sheath: there is no sheath integrated into the
`delivery system.
`FDA, U.S. Food and Drug Administration; EVAR, endovascular aneurysm repair; ePTFE, expandable polytetrafluoroethylene.
`
`stent with suprarenal
`
`active (hooks) fixation
`
`The Cook Zenith Flex device (Bloomington, IN)
`had long been the only FDA-approved endoprosthesis
`capable of treating 32-mm proximal aortic necks (the
`Zenith accomplishes this with a 36-mm graft),7 until the
`Powerlink 34-mm aortic cuffs and Medtronic Talent
`were approved in 2008. Its design is remarkable for a
`pararenal uncovered stent with active fixation (hooks), as
`demonstrated in the inset to Fig. 1A.
`Medtronic (Minneapolis, MN) currently markets
`two endografts for infrarenal AAAs. The AneuRx device
`is marketed in part as the device with the smallest
`
`delivery system to treat a 26-mm aortic neck: the
`AneuRx 28-mm proximal main body comes with in a
`21-French (outer diameter) integrated sheath.8 The
`AneuRx has no active fixation: neither proximal hooks
`nor the ability to rest on the aortic bifurcation (Fig. 1B).
`Possibly because of the more complete long-term sur-
`vival data amassed in studies of this graft, the FDA has
`issued a series of warnings (most recently in 2008) that
`late aneurysm-related mortality may be higher in pa-
`tients treated with the AneuRx device than in those
`treated with conventional open surgery.9
`
`Figure 1 Currently available Food and Drug Administration–approved stent grafts for treatment of abdominal aortic
`aneurysm. (A) Zenith. (B) AneuRx. (C) Talent. (D) Powerlink. (E) Excluder.
`
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`DEVICES USED FOR EVAR/JACKSON, CARPENTER
`
`41
`
`Table 2 Largest Proximal Neck Treated: Current
`FDA-Approved Devices
`
`Device
`
`AneuRx
`
`AAAdvantage
`
`Excluder
`
`Zenith Flex
`
`Powerlink
`
`Talent
`
`Largest Neck
`Treated (mm)
`
`Sheath (OD) to
`Treat 26-mm
`Proximal Neck (Fr)
`
`26
`
`26y
`32
`
`32
`
`32
`
`21
`
`21*
`
`24
`
`22
`
`24
`
`*In contrast to the other stent grafts listed, the Gore Excluder is
`delivered through a separate sheath: there is no sheath integrated
`into the delivery system.
`yThe Excluder 31-mm device can treat 27-mm to 29-mm aortic
`necks, but
`it
`is currently available in the United States for
`investigational use only. The sheath that Gore markets to deliver
`the 28-mm aortic endoprosthesis is 18-Fr with an OD of 21-Fr.
`FDA, U.S. Food and Drug Administration; OD, outer diameter; Fr,
`French.
`
`The Talent device is also manufactured by Med-
`tronic and is the only FDA-approved device whose on-
`label instructions for use allow treating aortic necks as
`short as 10 mm.10 The Talent is a modular bifurcated
`graft, but given the large variety of main body config-
`urations, repair can often be accomplished with a two-
`piece design. Although the Talent has no active fixation
`by proximal hooks,
`it does incorporate a suprarenal
`uncovered stent (Fig. 1C).
`The Powerlink device, from Endologix (Irvine,
`is the only currently marketed device that is
`CA),
`described as ‘‘unibody,’’ as opposed to modular bifur-
`cated.11 (Contrast Fig. 1D with the other devices de-
`picted in Fig. 1.) Among the benefits of this system are:
`(1) contralateral access is accomplished—usually percu-
`taneously—with a very small-diameter
`sheath (9-
`French), and (2) the usually obligatory—and often
`time-consuming—contralateral gate cannulation is ren-
`dered unnecessary by the unibody design.
`Recently, Endologix has obtained FDA approval
`for some new components of its system,
`including
`suprarenal extensions (comprising an uncovered stent
`proximal to an aortic cuff), 34-mm aortic cuffs capable of
`treating proximal necks up to 32 mm in diameter, and
`iliac limb extensions with distal diameters of 25 mm
`capable of treating iliacs up to 23 mm.
`Finally, Gore (Flagstaff, AZ) produces the Ex-
`cluder device for EVAR.12 This device is distinct from
`all of the above endografts in that it is delivered through
`standard percutaneous introducer sheaths; there is no
`sheath incorporated into the delivery system. This ap-
`proach to stent-graft insertion is compelling in its
`flexibility and adaptability, especially in the situation of
`small or otherwise difficult iliofemoral access vessels.
`Using the Gore device, it is most often possible to design
`a two-piece repair of an AAA, given the vast variety of
`diameters and lengths of the integrated main body and
`
`ipsilateral limb graft (Fig. 1E). Earlier versions of the
`Excluder had lower rates of aneurysm sac shrinkage than
`with other devices; most recently, a ‘‘low-permeability’’
`version is manufactured and preliminary results indicate
`that it is less prone to ‘‘endotension’’ (sac expansion in
`absence of demonstrable endoleak). Although Gore
`plans the addition of devices with larger-diameter prox-
`imal aortic necks, currently the largest device is 28.5 mm
`proximally, which is able to treat up to 26-mm necks.
`This is smaller than other current FDA-approved de-
`vices, except the AneuRx endoprosthesis.
`One additional EVAR device had been FDA
`approved: the Ancure device from EVT, a subsidiary
`of Guidant, was FDA-approved in 1999, but its approval
`was suspended in 2001 due to nonreporting of many
`device failures and adverse patient outcomes. Subse-
`quently reapproved, Guidant stopped manufacturing
`the device in 2003.
`Several other devices have undergone FDA-sanc-
`tioned trial in the United States. The Edwards Lifepath,
`a balloon-expandable modular bifurcated graft, suffered
`from stent fractures of the main body.13 The Cordis
`Fortron incorporated transrenal fixation but has never
`come to market.14 Finally, the Trivascular Enovus device
`was deliverable through a small-diameter sheath because
`its support structure was in part derived from injectable
`polymer.15 The Enovus also employed a ‘‘gasket’’ at its
`proximal seal zone, with the capability to seal in angled or
`calcified necks, which,
`in necks with circumferential
`thrombus, may be augmented by iterations on this device,
`similar designs, or other mechanisms such as ‘‘staples.’’16
`
`FUTURE
`Required secondary interventions during long-term fol-
`low-up of patients having undergone EVAR, to prevent
`aneurysm-related mortality, partially offset early advan-
`tages in recovery and perioperative mortality as com-
`pared with open repair.17 Therefore, device design to
`maximize the durability of EVAR and safely minimize
`the requirements for follow-up and monitoring will
`continue to be sought after.
`Increasing the applicability of EVAR to patients
`with difficult anatomic features will
`likewise require
`improvements and innovation in device design. The
`three most common anatomic reasons for exclusion
`from endovascular repair of AAAs are inappropriate
`aortic (proximal) neck, iliac artery aneurysms, and in-
`adequate iliac access.18,19
`The next frontier of endovascular AAA repair is
`clearly the continued adoption and development of
`endografts capable of treating juxtarenal, pararenal, and
`thoracoabdominal aortic aneurysms.
`Therefore, the challenges for the next generation
`of EVAR devices are: (1) increasing the durability of
`stent-graft repair, (2) refining and redesigning grafts to
`
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`42
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`SEMINARS IN INTERVENTIONAL RADIOLOGY/VOLUME 26, NUMBER 1 2009
`
`Table 3 EVAR Devices Currently in Trial or Limited Use
`
`Device
`
`Manufacturer
`
`Stent Material
`
`Fabric Material
`
`Delivery System
`
`Anaconda
`
`Vascutek
`
`Nitinol
`
`Woven polyester
`
`Integrated sheath
`
`Aorfix
`
`Lombard
`
`Nitinol
`
`Woven polyester
`
`Integrated sheath
`
`Aptus
`
`Aptus
`
`Nitinol
`
`Woven polyester
`
`Integrated sheath
`
`Endurant
`
`Metronic
`
`Nitinol
`
`Woven polyester
`
`Integrated sheath
`
`Distinctive Features
` Repositioning capability
` Magnetic guidance for cannulation
`of contralateral gate
` Circumferential ring stents and
`‘‘crumple zones’’
` May provide flexibility for
`angulated necks
` Small delivery system (16 Fr)
` Endostaples
` Pararenal uncovered stent with
`suprarenal active (hooks) fixation
`
`EVAR, endovascular aneurysm repair; Fr, French.
`
`allow treatment of today’s ‘‘difficult’’ anatomic features,
`and (3) advancing our abilities to treat aneurysms in-
`volving the renal and visceral segments of the aorta.
`
`Future Devices
`Several endografts for EVAR are currently on trial in the
`United States or are awaiting FDA approval (Table 3).
`The Anaconda device, developed by Vascutek, is cur-
`rently in the FDA approval process.20,21 It is purported
`to provide facile contralateral gate cannulation, owing to
`a unique dual-wire system equipped with magnets,
`flexible delivery system, and—most remarkably—the
`capacity to collapse and reposition after the proximal
`neck (with active fixation hooks) has been deployed. In
`addition, the proximal ring stent has a saddle-shaped
`stent, allowing a portion of the proximal device to be
`placed at and above the renals, without actually covering
`the ostia.
`The Aorfix device, from Lombard, features cir-
`cumferential
`ring stents with intervening ‘‘crumple
`zones’’ at its proximal seal zone, in an attempt to allow
`treatment of more angulated hostile necks.22
`The Aptus endoprosthesis incorporates novel
`proximal neck screws, or ‘‘endostaples,’’ providing fixa-
`tion of the graft to the transmural aorta. The device
`requires only a 16-French delivery system. The pivotal
`trial is currently underway in the United States.
`Medtronic has a novel device, called Endurant,
`which is currently being used in Europe, with upcoming
`trials in the United States. This device incorporates both
`the pararenal uncovered stent that the company utilizes
`in its Talent endoprosthesis and active fixation hooks
`proximally.
`
`ment. That said, a couple of these improvements are
`either currently in trial or are widely anticipated. Since
`2003, Gore has marketed a 31-mm Excluder device for
`sealing proximal necks up to 29 mm. This device has
`been trialed in the United States but is not currently
`available for regular use. A ‘‘next-generation’’ Cook
`Zenith device is in development: among its features is
`a greatly reduced sheath diameter (reportedly, 16-
`French to 18-French outer diameter).
`
`Fixation
`Current approaches to fixation of grafts—to prevent
`migration, especially of the proximal graft from its
`implanted juxtarenal position—include: (1) radial force;
`(2) hooks, anchors, or barbs to embed in the aortic wall;
`(3) columnar stiffness of the graft with distal anchoring
`in the iliacs or on the aortic bifurcation (the Powerlink
`device). Hooks may be positioned in either the infrarenal
`portion of the graft (the Gore Excluder) or in the para-
`renal uncovered stent (Zenith and Endurant devices).
`The Aptus device attempts to address this issue in a novel
`and unique manner, as discussed previously.
`
`Branched and Fenestrated Endografts
`Branched grafts, fenestrated grafts, or some combination
`thereof may potentially extend EVAR to AAAs with
`short or ‘‘difficult’’ proximal necks, as well as to juxtare-
`nal and suprarenal aneurysms.23 The first reported ex-
`perience with fenestrated endografts to treat aortic
`aneurysms with branch vessel ostia in the anticipated
`seal zone came in 1996 from Park et al.24 Subsequently,
`the Cleveland Clinic group has reported their experience
`with a Cook fenestrated device.25,26
`
`Improvements to Current Devices
`The various companies with FDA-approved EVAR
`devices are all fairly secretive with respect to novel
`devices, components, or features currently in develop-
`
`Branched Iliac Grafts
`In current practice, common iliac involvement in aneur-
`ysmal change (aortoiliac aneurysm) is most often treated
`
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`DEVICES USED FOR EVAR/JACKSON, CARPENTER
`
`43
`
`with embolization of the ipsilateral internal iliac (except
`in ruptured AAAs) and coverage of the ostium of that
`vessel by landing and sealing the stent-graft limb in the
`external iliac. However, this approach has several dis-
`advantages: it is seldom utilized in cases of bilateral
`common iliac aneurysms (owing to the high risk of
`colonic ischemia),
`it can result in ipsilateral gluteal
`claudication, and it makes iliac stent-graft limb patency
`entirely dependent on femoral outflow, which can be
`compromised in patients with atherosclerosis who have
`undergone femoral access and repair. Early iterations of
`devices incorporating branched iliac endografts have
`been reported but are not currently on trial in the United
`States.
`
`DISCUSSION
`The two most frequently encountered barriers to EVAR
`are inadequate or inappropriate proximal neck anatomy
`and inadequate caliber of iliofemoral access vessels.
`Hence, the abilities of any device, present or future, to
`accommodate patients with difficult necks or treacherous
`access vessels are important, even essential. Novel bifur-
`cated endografts and the development of widely available
`branched and fenestrated grafts will help address these
`barriers, building upon the remarkable clinical success of
`the past and current generations of endovascular pros-
`theses for the treatment of AAAs.
`
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