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In a more actual study, all of the 14 patients with IAAAD were treated by endovascular means, with an important primary technical success of 100%, low mortality rate, and good outcomes. However, in the clinical setting of IAAAD, data
remain inconclusive [8,13].
There is also the problem of branch obstruction and the visceral or peripheral ischemia, which are in most cases the main
cause of serious complications. There are multiple mechanisms involved. The most common are caused by the dissection
flap lying and/or entering into the origin of the vessels, branches arising from the low circulated false lumen, thrombosis or
embolization into the branches or preexisting atherosclerotic lesions.
One of the most utilized treatment options in this situation is the aortic fenestration, a method that decompresses the
false lumen by creating a hole in the distal part of the dissection. Open surgery fenestration is now a part of history, but
percutaneous fenestration is now a good alternative with low procedural risk.
The need for visceral stenting or fenestration in conjunction with endovascular grafting remains controversial. Some
authors suggested that adjunctive stents within dissected branch vessels are unnecessary [16], even though more other
studies showed that the decision to stent a branch prior of the endovascular treatment is dependent on the time required to
perform this procedure and the risk of the branch vessel occlusion [17].
REFERENCES
[1] Peacock TB. Edinburgh Med Surg J 1843;60:276.
[2] Peacock T.B. Transactions of the Pathological Society of London. ;14:106.
[3] Laennec RTH. 2nd ed. Traite de l’auscultation Mediate et des Maladies des Poumnons et du Coeur. 1826, vol. 2, p. 696. Paris.
[4] Roberts CS, Roberts WC. Aortic dissection with the entrance tear in the abdominal aorta. Am Heart J 1991;121:1834–5.
[5] Trimarchi S, Tsai T, Eagle KA, Isselbacher EM, Froehlich J, Cooper JV, et al. International Registry of Acute Aortic Dissection (IRAD) investiga-
tors. Acute abdominal aortic dissection: insight from the International Registry of Acute Aortic Dissection (IRAD). J Vasc Surg 2007;46:913–9.
[6] Becquemin JP, Deleuze P, Watelet J, Testard J, Melliere D. Acute and chronic dissections of the abdominal aorta: clinical features and treat- ment.
J Vasc Surg 1990;11:397–402.
[7] Graham D, Alexander JJ, Franceschi D, Rashad F. The management of localized abdominal aortic dissections. J Vasc Surg 1988;8:582–91.
[8] Kouvelos GN, Vourliotakis G, Arnaoutoglu E, et al. Endovascular treatment for isolated acute aortic dissection. J Vasc Surg 2013;58:1505–11.
[9] Le Pimpec-Barthes F, Kieffer E. Traumatismes ferme′s de l’aorte ab- dominale. In: Kieffer E, editor. Traumatismes arte riels. Paris: AERCV; 1995.
p. 407–25.
[10] Graham D, Alexander J, Franceschi D, et al. The management of localized abdominal aortic dissections. J Vasc Surg 1988;8:582–91.
[11] Peterson AH, Williams DM, Rodriguez JL, et al. Percutaneous treatment of a traumatic aortic dissection by balloon fenestration and stent placement.
AJR Am J Roentgenol 1995;164:1274–6.
[12] Farber A, Wagner WH, Cossman DV, Cohen JL, Walsh DB, Fillinger MF, et al. Isolated dissection of the abdominal aorta: clinical presentation and
therapeutic options. J Vasc Surg 2002;36:205–10.
[13] Jonker FH, Schlösser FJ, Moll FL, Muhs BE. Dissection of the abdominal aorta. Current evidence and implications for treatment strategies: a review
and meta-analysis of 92 patients. J Endovasc Ther 2009;16:71–80.
[14] Berthet JP, Marthy-Ane CH, Veerapen R, et al. Dissection of the abdominal aorta in blunt trauma: endovascular or conventional management? J Vasc
Surg 2003;38:997–1004.
[15] Mantelas M, Antonitsis P, Kaitzis D, Hatzibaloglou A, Moros I. Spontaneous isolated dissection of the abdominal aorta: single-center experience.
Interact Cardiovasc Thorac Surg 2009;8:398–401.
[16] Dake MD, Kato N, Mitchell R, Semba CP, Razavi M, Shimono T, et al. Endovascular stent-graft placement for the treatment of acute aortic dissec-
tions. N Engl J Med 1999;340(20):1546–52.
[17] Greenberg R, Khwaja J, Haulon S, Fulton G. Aortic dissections: new perspectives and tratement paradigms. Eur J Vasc Endovasc Surg 2003;26:579–86.
Chapter 37
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The Various Types of Endovascular Stent
Grafts for EVAR: How Do They Compare?
Efstratios Georgakarakos, Nikolaos Schoretsanitis
“Democritus” University of Thrace, University Hospital of Alexandroupolis, Alexandroupolis, Greece
Chapter Outline
Introduction 415
Technical Characteristics of Commercially Available Endografts 416
Endografts With Active Fixation and Sealing via Outward
Radial Force 416
Direct Accommodation Onto the Aortic Bifurcation 416
A Novel Mode to Dissociate Fixation and Sealing 417
Introducing Endovascular Aneurysm Sealing 417
Anatomic Suitability of Different Endografts in AAA 417
Comparing the Clinical Efficacy Between Various Endografts 417
Mechanical Differences Between Endografts 418
The Impact of Nitinol Configuration on the Iliac Limbs of
Endografts 418
Effect of EVAR on Arterial Wave Reflection 418
The Influence of Various Stent Grafts on the Infrarenal Neck 419
Discussion 419
References 419
INTRODUCTION
Since its introduction in 1991, the endovascular repair (EVAR) of abdominal aortic aneurysms (AAA) has been widely
accepted by physicians and patients due to its minimal invasive nature and its lower perioperative mortality and morbidity [1,2]. The first endograft was implanted by Juan Parodi in 1991 and was handmade, extremely rigid, with a large
profile. Since then, the stent-graft technology has evolved rapidly and newer endografts have been introduced in the
market, widening the eligibility for EVAR [3,4]. The ideal endograft should accommodate to the infrarenal neck to
ensure adequate sealing and provide fixation to resist to the forces that predispose to migration with a subsequent loss of
sealing (central and peripheral endoleaks Ia and Ib, respectively) and repressurization of the aneurysmal sac. Its delivery
system should be flexible, with hydrophilic coating and low profile to facilitate navigation through tortuous and stenotic
iliac vessels.
Over the last two decades, significant modifications have taken place to evolve the mechanical enhancement of
the aortic endografts and, hence, their practical applicability and clinical performance in the long run [5]. As such,
there are different fabric (woven polyester and (polytetrafluoroethylene) PTFE) and skeleton (nitinol, stainless steel
or cobalt chromium alloy) designs among the endografts; most importantly, significant variations exist in the sealing
and/or fixation modes with infrarenal and suprarenal fixation with pins, hooks, and barbs accompanying the integrated suprarenal stents existing in the vast majority of endograft patterns. There are two configurations of stent grafts
for AAA repair: (1) the bifurcated graft and (2) the aortouniiliac configuration (AUI) with contralateral common iliac
artery occlusion and femorofemoral cross-over bypass.
Undeniably, the long-lasting clinical efficacy (AAA sac exclusion from systematic pressure, avoidance of sac
expansion or rupture) and incidence of complications leading to major interventions are the crucial reference
points when comparing the various endografts. However, this task may not be that simple as it sounds because
no direct comparisons between various endografts exist in the literature. Clinical registries, single- or multicenter studies (prospective or retrospective) provide mostly the data to compare. Moreover, apart from any form
of clinical studies, in vitro laboratory studies provide additional information about the biomechanical properties
of various endografts’ patterns and designs as well as the impact of the latter on the central hemodynamics of the
patients. This chapter provides useful clinical and hemodynamic information for the endografts commercially
New Approaches to Aortic Diseases from Valve to Abdominal Bifurcation. http://dx.doi.org/10.1016/B978-0-12-809979-7.00037-7
Copyright © 2018 Elsevier Inc. All rights reserved.
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available and discusses the major drawbacks and limitations between current data. Furthermore, we attempt to
delineate certain information regarding the mechanical properties of endografts and incorporate it into routine
clinical practice.
TECHNICAL CHARACTERISTICS OF COMMERCIALLY AVAILABLE ENDOGRAFTS
Endografts With Active Fixation and Sealing via Outward Radial Force
The C3 Gore Excluder is a third-generation device featuring an original design with a flexible, catheter-mounted introduction and active infrarenal attachment with barbs. It is a modular bifurcated system composed of PTFE. It is designed to be
a three-step process with the option of repositioning after deployment and before the release of the active fixation stent.
According to its instructions-for-use (IFU), this endograft is approved for infrarenal necks measuring ≥15 mm in length and
≤60 degrees angulation [6].
The Endurant II (Medtronic, Santa Rosa, CA) is a modular bifurcated stent graft composed of nitinol stents and polyester graft. The combination of the M-shaped configuration of nitinol stents and improved suprarenal active fixation with
anchoring pins provides better resistance to migration in short and angulated proximal aortic necks. It is approved for
infrarenal necks of ≥10 mm length with angulation ≤60 degrees or of 15 mm and ≤75 degrees. More recently, in November
2014, the new three-piece Endurant-IIs received Food and Drug Administration (FDA) approval [7].
The Zenith Flex (Cook Medical, Bloomington, USA) is a modular bifurcated system consisting of a stainless steel
Z-stents sutured to a woven polyester graft material. The proximal stent contains barbs for suprarenal fixation. The Zenith
Flex device is delivered through 18- to 24-Fr sheaths. The IFU includes a minimum 15 mm infrarenal neck and an infrarenal
angulation of ≤60 degrees. The new Zenith low profile is constructed of nitinol stents instead of stainless steel with a thinner
polyester material and its 16-F delivery system allows the treatment of patients with iliac diameters of 6 mm [8].
The Treo abdominal stent graft (Bolton Medical, Barcelona, Spain) is a tightly woven polyester nitinol trimodular endograft with a main bifurcated stent graft and two leg extensions. It is the only endograft to possess a combination of both
suprarenal and infrarenal fixation. The main body comes in three different lengths, whereas the overlapping length between
the main body and the limb extension is adjustable (40 mm adjustable landing zone for the ipsilateral and 10 mm for the
contralateral limb). Each iliac gate has five dull barbs to prevent the separation of the limbs from the main component.
According to its IFU, the Treovance is suitable for infrarenal necks ≥10 mm and angulation ≤60 degrees or a length ≥15 mm
and angulation 60–75 degrees [9].
The Incraft stent graft (Cordis, Bridgewater, NJ, USA) was designed to overcome the limitation of the small diameter
of the access vessels. It is a trimodular bifurcated device constructed of a seamless, low porosity, woven polyester graft
supported by a series of self-expanding nitinol stents throughout the entire graft. Suture knots on the outer surface of the
limb prosthesis serve as an interlocking mechanism to decrease the risk of limb disunion. The delivery system for the main
body has an outer diameter of 14 Fr. The Incraft endograft can be delivered through iliac vessels with diameters of 4.7 mm,
broadening the eligibility of EVAR [10].
The Anaconda One Lok stent graft (Vascutek, UK) is a three piece device made of nitinol rings and a polyester graft. Its
active infrarenal fixation is accomplished via eight hooks. A magnet system facilitates the cannulation of the contralateral
gate. It requires an infrarenal neck length ≥15 mm [11].
The E-vita stent graft (Jotec, Hechingen, Germany) is a modular two-piece endograft with suprarenal fixation composed
of polyester fabric and nitinol stents. The IFU includes an infrarenal neck length of ≥15 mm with angulation ≤60 degrees
and an iliac diameter of 11–23 mm. The delivery system starts at 16 Fr for the extensions and 20 Fr for the main body [12].
Its most recent development, E-tegra, features the squeeze-to-release deployment mechanism for the most precise positioning and handling. Its IFU includes a neck length ≥15 mm, a neck diameter of 19–32 mm, an infrarenal angulation≤75
degrees and an iliac diameter between 8 and 25 mm.
The Aorfix stent graft (Lombard Medical Technologies, Oxfordshire, UK) is composed of nitinol rings on a polyester
fabric. The rings are deformed to have a saddle or fish mouth shape. This shape allows the rings to be placed transrenally
with the fish mouth trough aligned with the renal arteries juxtarenally and the fish mouth peak extending suprarenally. The
IFU includes a neck length of ≥20 mm and a neck diameter of 19–29 mm. It is the only available endograft that can be used
in infrarenal angulation up to 90° [13].
Direct Accommodation Onto the Aortic Bifurcation
The AFX stent graft (Endologix, Inc, Irvine, CA, USA) is a unibody endograft based on the concept of anatomic fixation. It contains a proximal extension (suprarenal or infrarenal) that seals to the aortic neck by exertion of radial force.
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The stents of the AFX device (made of cobalt-chromium) are sutured on the inside of the graft material and only at
the proximal and distal ends of the graft allowing the movement of the graft material outside the stents. Therefore, the
graft material accommodates to the irregularities of the aortic neck (angulation, calcification, thrombus), whereas an
inflexible material might fail to do. A significant advantage of the AFX is the efficacy to manage patients with narrow
bifurcation (≤15 mm) because the limited aortic space in such cases may prohibit the complete expansion of the iliac
limbs of a bifurcated endograft. The IFU includes an infrarenal neck length ≥15 mm, a neck diameter 18–32 mm, an
infrarenal angulation <60°, and an iliac sealing diameter of 10–32 mm [14].
A Novel Mode to Dissociate Fixation and Sealing
The Ovation-prime aortic stent graft separates fixation from sealing by means of a pair of compliant, inflatable rings
filled with a low-viscosity radiopaque polymer. The conformable paired O-rings guarantee a precise accommodation
onto the neck surface irrespective of the degree of calcification or the amount of neck thrombus. The Ovation stent
graft does not depend on the length of neck as long as the first ring seals 13 mm below the inferior renal artery in a
diameter ≤30 mm [15].
Introducing Endovascular Aneurysm Sealing
The endovascular aneurysm sealing (EVAS) philosophy was recently introduced with the Nellix system (Endologix, Inc,
Irvine, CA, USA) offering an alternative approach to endovascular treatment of AAA. This endograft consists of dual
balloon-expandable endoframes, each surrounded by a polymer-filled endobag, to achieve anatomical fixation in the aneurysm sac, dissociating the sealing efficiency from the shape and contour of the proximal aortic neck. The endobags fill
the aneurysm sac obstructing the side branches, and therefore, EVAS has the potential to reduce the incidence of type II
endoleaks. The Nellix stent graft is particularly suitable for patients with conical necks as the endobags apply on the entire
length of the conical neck elongating the sealing zone [16].
ANATOMIC SUITABILITY OF DIFFERENT ENDOGRAFTS IN AAA
The anatomic suitability for EVAR according to the IFU of three commercially available bifurcated grafts (Zenith
Flex, Excluder, Endurant) was recently compared by Kristmundson et al. [17]. The computed tomography (CT) scans
of 241 patients with AAAs were evaluated with regards to the anatomic suitability of these AAA for each of the three
endografts. They concluded that the suitability (by brand) was 28.6% for the Zenith, 25.7% for Gore Excluder, and
48.1% for the Endurant. Narrow iliacs, short necks, and combination of these factors were the commonest reasons
for nonsuitability. Additionally, Van Keulen et al. compared the suitability of Zenith, Excluder, Talent, and Endurant
stent grafts in 100 patients treated originally with the Endurant device [18]. The anatomic suitability of these AAA
for each of the aforementioned alternative endografts (Zenith, Excluder, Talent) was 52%, 60%, 73%, and 81%,
respectively. Again, the Endurant showed the greatest suitability, but a significant proportion of patients were still
treated outside the IFU.
COMPARING THE CLINICAL EFFICACY BETWEEN VARIOUS ENDOGRAFTS
In a retrospective comparison between newer endografts (Endurant, Zenith, low-porosity Excluder and second generation
Anaconda) and older ones (AneuRx, Fortron, Talent, first generation Excluder and first generation Anaconda), Verzini et al.
documented higher freedom from reintervention and late conversion, (83.6% vs. 74.2%, 96.1% vs. 89.1) as well as from
AAA sac growth for the newer endografts at 7 years [19]. In another single institution study comparing the Endurant stent
graft with its predecessor (Talent), the rate of Type I endoleaks was higher for the Talent group (5.7% vs. 2.8%, P = .614),
type III endoleaks occurred only in the Talent group (2.9% of patients; P = .493) while type II endoleaks were significantly
more common in the Talent group (28.6% vs. 8.3%; P = .035). These results suggest that the newer Endurant endograft has
better outcomes than its predecessor despite the higher incidence of patients with challenging anatomy in the Endurant
group (41.7% kinking of the iliac arteries in the Endurant group vs. 14.3% in the Talent group; P = .017 and mean proximal
neck length of 3.96 ± 0.19 cm in the Talent group versus 3.21 ± 1.35 cm in the Endurant group; P = .084). The higher incidence of migration and higher incidence of Type I endoleaks for Talent versus Endurant stent graft has been well reported
in the literature [20–22].
It is known that the regression of the aneurysmal sac after EVAR is an accepted indicator of aneurysm exclusion
and clinical success. Cieri et al. studied the effect of the stent graft type on aneurysm shrinkage in 1450 patients
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undergoing EVAR at a single center over a 10-year period. Persistent shrinkage was defined as a ≥5 mm regression
of the AAA sac diameter persisting or increasing until the end of follow-up, without reintervention. During a median
follow-up of 45 months, persistent shrinkage was detected in 768 (53%) aneurysms. Persistent shrinkage rates were
significantly higher for Zenith (P < .0001), Endurant (P = .013), and Excluder (P < .0001) devices. Cox analyses confirmed that persistent shrinkage rates were independently associated with the Zenith and Endurant endografts and
negatively associated with the older generation AneuRx device. The authors concluded that last generation devices
seem to be important factors in inducing aneurysm sac shrinkage with similar clinically relevant effects among
single models [23].
On the contrary, the newer endografts present similar outcomes. Early results from the GREAT registry (Global
Registry for Endovascular Aortic Treatment) registry are comparable to the results of the ENGAGE (Endurant Stent
Graft Natural Selection Global Postmarket Registry) for Endurant, in terms of initial technical success (both 99.0%),
30-day mortality (0.5% in GREAT vs. 1.3% in ENGAGE), and estimated survival at 1-year (96% in GREAT vs.
91.6% in ENGAGE) [6,24]. Estimated freedom from reintervention at 1-year was also similar between the two registries (95.2% in GREAT vs. 95.1% in ENGAGE). Interestingly, the main difference was the leading cause for reintervention. The 46.2% of all reinterventions in the GREAT registry was aimed at the treatment of type II endoleaks,
whereas the main reason for reintervention in the ENGAGE registry was the iliac limb graft thrombosis (3.4%). The
abovementioned registries represent the performance of an endograft with active suprarenal fixation (Endurant) and
the performance of an endograft with active infrarenal fixation (Excluder C3) in real-world conditions, i.e., enrollment of patients who fell outside the IFU criteria was accepted for both grafts (17% in the GREAT vs. 17.9% in the
ENGAGE) [6,24]. Interestingly, no migration was observed in both registries showing no difference in the migration
incidence between the suprarenal and infrarenal fixation mode. The same observation was confirmed by Hager et al.
The authors compared the outcomes between the Zenith and the Excluder in short aortic necks <15 mm and infrarenal
angulation <60 degrees, documenting no difference in the incidence of migration and type Ia endoleaks [25].
MECHANICAL DIFFERENCES BETWEEN ENDOGRAFTS
The Impact of Nitinol Configuration on the Iliac Limbs of Endografts
Demanget et al. investigated the mechanical performance of eight different endograft limbs using finite element analysis. The authors concluded that spiral and circular spiral stents may provide lower stress values, better flexibility, and
better durability compared to Z-stents [26,27]. For angulation greater than 60°, the Aorfix limb was more flexible than
the Zenith limb. This flexibility may decrease the incidence of complications in the setting of tortuous aortoiliac aneurysms. Because the iliac limb graft occlusion represents an important cause of reintervention after EVAR, it becomes
apparent that further research should focus on comparing spiral, circular, and Z-shaped stents of various endografts.
Effect of EVAR on Arterial Wave Reflection
The implantation of an aortic stent graft for treatment of AAA has been shown to influence the aortic stiffness quite
early postoperatively [28,29]. Such effect may be differentiated not only by the endograft’s fabric but also by the type
of endoskeleton (nitinol or stainless steel) [30–32]. Kadoglou et al. documented a greater PWV (pulse wave velocity)
elevation in patients treated with polyester-covered stent grafts [31]. Wave reflection takes place at all bifurcations
and discontinuities of the vasculature. Normally, the major part of the reflections takes place at the arterioles, i.e.,
there may be bifurcations present over short distances [33]. In addition, there appears to be a distinct reflection site
in the distal abdominal aorta. The moment the reflected pressure wave returns at the heart depends on the distance
of the reflection site from the heart, the pressure wave speed and the wall mechanical properties at the reflection site
(i.e., the phase of reflection coefficient). The majority of recent reports have focused solely on the influence of EVAR
on aortic PWV as a surrogate of aortic stiffness [28–34]. Moreover, the increase of aortic systolic blood pressure
due to wave reflections (Augmentation Index) represents an additional marker of arterial stiffness or the impedance
that the increased stiffness of the infrarenal aorta (where the endograft is hosted) posed to the normal arterial wave
transmission.
The arrival time of the backward pressure waves has a crucial role; if this reflected pressure wave component arrives
before the aortic valve closure, then the left ventricular afterload will be elevated and additional myocardial work will be
needed to overcome this. Therefore, an increase of Augmentation Index along with the coinciding decrease of the reflection
magnitude in almost all cases shows that peripheral vasoconstriction can modify the pressure wave reflection toward the
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ascending aorta (centrally) and the amplitude of the backward- and the forward wave (reflection magnitude). The critical
issue of myocardial performance remains the most critical task to be investigated postinterventionally because previous
studies have associated PWV and AI@75 (augmentation index) with adverse cardiovascular events [34–36].
The Influence of Various Stent Grafts on the Infrarenal Neck
The chronic outward radial pressure exerted on the AAA neck by the Nitinol-skeleton endografts has been implicated
in the AAA neck distention, which facilitates dislodgement of the endograft and migration with resultant loss of sealing
and generation of central endoleaks. Malas et al. observed no significant neck dilatation in a series of AAA treated with
balloon-expandable stent grafts (BES) in a mean-follow-up periods of 31 months [37], whereas Monahan et al. reported
a continuous post-EVAR neck dilatation when treated with a self-expandable stent grafts [38]. Dalainas et al. identified
also a significantly higher rate of dilatation in 200 AAA patients treated with SES compared to those managed with SES
(27.5% vs. 7.1%, P = .023) [39]. Most recently, Savlovskis et al. not only confirmed the continuous dilating effect of SES
on AAA neck but also the absence of expansion with the newest Nellix BES endograft [40]. Additionally, de Donato et al.
measured no significant neck enlargement in any of 88 AAA patients treated with the Ovation stent graft in a multicenter
registry of 161 patients with a mean follow-up period of 32 months [40]. So, there seems that stent grafts that ensure sealing without exerting a continuous radial force protect the AAA infrarenal neck from enlargement and consequent need for
future interventions.
DISCUSSION
Although comparing the clinical performance of different endografts may sound easy, there are certain barriers and
limitations toward this pathway. Although randomized controlled trials constitute the gold standard for the assessment
of surgical innovations, the distinctive characteristics of these studies limit their applicability in clinical practice,
especially with respect to the direct comparison between endografts [41]. The time needed for requirement, assessment, and analysis of evidence from randomized controlled trials poses a difficulty in keeping up pace with the rapid
evolving technology and evolution in endograft designs. The ongoing and evolving technologies, the new technique
advances, and increased operator experience, which can also significantly affect the results of evaluation of endografts’ performance, can be adapted and reflected more easily in cohort studies, registries, single-center prospective
studies, etc. On the other hand, the bias in selection of cases, the under-reporting of least favorable results, the difference in experience between various centers and the lack of a thorough, standardized format in reporting the anatomic
characteristics of the treated AAA render the direct comparison of synchronous endografts cautious, if not difficult.
So, there seems that the only safe comparison is between endografts of older and newer generations. Hence, according
to the UK’s 2009 National Institute for Health and Clinical Experience (NICE) appraisal, long-term complications
following EVAR in randomized controlled trials were higher than those documented in current UK practice [41].
Therefore, it is imperative that a detailed standardized reporting format should be universally introduced to upgrade
the comparison—even indirectly—among endografts.
Furthermore, the evolution and improvement of the endograft armamentarium provide the clinicians with more therapeutic options than before. Hence, one has to be aware of the intrinsic mechanical properties and technical characteristics
of each device to provide a more patient-specific therapeutic solution. For example, different length-ratios in AAA of same
maximum transverse are associated with different tendency for displacement and migration of endografts from the fixation sites, whereas newer stent grafts whose fixation is based on polymer inflation, Nitinol-free design may serve better
AAA with marginal diameter of infrarenal neck (i.e., acting no outward force and eliminating the risk of enlargement of
a 28–30 mm neck) [42]. Moreover, noninvasive modalities of assessing and comparing the effect of different endograft
designs on central hemodynamics and myocardial performance of recipients may not only help in the improvement of
future stent grafts but also contribute to the optimal choice for some patients with impairment of myocardial function.
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[15] Georgakarakos E, Ioannou CV, Georgiadis GS, Storck M, Trellopoulos G, Koutsias S, Lazarides MK. The ovation abdominal stent graft for the
treatment of abdominal aortic aneurysms: current evidence and future perspectives. Expert Rev Med Devices 2016;13(3):253–62.
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Chapter 38
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Endovascular Stent-Graft Repair of
Abdominal Aortic Aneurysms
Joel A. Lardizabal, Sanjiv S. Sharma
Bakersfield Heart Hospital, Bakersfield, CA, United States
Chapter Outline
Background 423
Indications for EVAR 424
Anatomic Criteria for EVAR Device Eligibility 424
Preoperative Imaging 427
Vascular Access 427
BACKGROUND
The EVAR Device 428
Stent-Graft Deployment 428
Endoleaks 429
Post-EVAR Surveillance Imaging 430
References 430
Abdominal aortic aneurysm (AAA) is a significant public health burden as up to 12.5% of men aged 75–84 years is afflicted
by clinically significant forms of this condition. Although the attributable mortality rate has declined by 15% in the United
States, the total deaths from AAA actually increased from 99,600 in 1990 to 151,500 in 2013 because of a growing and
aging population [1].
The natural history of AAA is the progressive expansion (large aneurysms expand more rapidly than smaller ones) and
the development of mural thrombus because of turbulent flow within the sac. These features are responsible for the three
most common complications of AAA: rupture, thromboembolic events, and mass effect/compression of adjacent structures.
Rupture is the most catastrophic complication of AAA. Mortality approaches 90% as most patients die before reaching
the hospital [2]. Outcomes are grim even for those who make it to the hospital, as death rates remain as high as 53%–66%
(lower inpatient mortality is observed in areas where intervention rates are higher) [3].
Since its inception in the 1950s, open surgical resection and graft replacement had been the mainstay of definitive
therapy for clinically significant AAA. Although the procedure is highly effective in lowering the overall mortality from
AAA, open repair is highly invasive and associated with major morbidity. Operative mortality for open surgical repair
approaches 50% for ruptured AAA and is nearly 5% for intact aneurysms [4]. Furthermore, many high-risk patients with
multiple comorbidities are often deemed inoperable and denied the potential benefits of AAA intervention.
The need for a safer, less invasive approach to AAA repair has led to the development in the mid-1980s of intraluminal
graft devices that could be deployed through endovascular techniques [5–7]. This revolutionary endovascular abdominal
aortic aneurysm repair (EVAR) procedure was successfully performed in humans in 1990. The prosthetic device comprised
of a tubular Dacron graft with balloon-expandable stents sutured at both ends. The graft was delivered via catheter into
the aorta through common femoral artery access under local or regional anesthesia. When deployed, the stents fixed the
ends of the graft to the aortic wall, directing the blood flow through the graft lumen and excluding the aneurysm from the
circulation [8].
Subsequent technological advances in the design of the stent graft and delivery device, as well as continuous
improvements in procedural techniques, have led to the rapid development and wide acceptance of EVAR as a safer
alternative to open surgical repair of AAA. It also expanded the treatment base to include high-risk patients who
were previously deemed inoperable. Compared to open repair, EVAR has significantly lower operative mortality
for both ruptured AAA (27% vs. 46%) and elective intervention (1.2% vs. 4.6%). Epidemiologically, a significantly
lower inpatient mortality for AAA rupture is observed in areas where the uptake of EVAR is higher [3]. Overall, the
AAA mortality has declined steeply after the introduction of EVAR. By 2005, EVAR has surpassed open repair as
New Approaches to Aortic Diseases from Valve to Abdominal Bifurcation. http://dx.doi.org/10.1016/B978-0-12-809979-7.00038-9
Copyright © 2018 Elsevier Inc. All rights reserved.
423
424 PART | III Treatment
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the predominant treatment modality, accounting for 56% of all intact AAA repairs in the United States. Utilization
of EVAR continued to rise to 75% by 2010; inhospital mortality and length of stay significantly declined during this
period [1].
INDICATIONS FOR EVAR
The same indications for open surgical repair of AAAs apply for EVAR, provided the required anatomic eligibility criteria
specific for each device are met. The patient must also be able to comply with periodic long-term surveillance imaging to
monitor for endoleak, stability of the aneurysm sac, and integrity of the stent graft.
Emergent intervention is indicated for AAA rupture, which classically presents with the clinical triad of abdominal/back
pain, pulsatile abdominal mass, and hypotension. EVAR is indicated for symptomatic AAAs regardless of size. Symptoms
may be associated with compression or erosion of surrounding structures from mass effect and thromboembolic events
from mural thrombus.
For asymptomatic patients, eligibility primarily depends on aneurysm size as it is the strongest predictor of AAA
rupture. Risk of rupture is low for sac diameter below 4 cm. Eventual rupture risk is approximately 20% for aneurysm
diameter over 5 cm, 40% above 6 cm, and 50% above 7 cm. To eliminate the risk of rupture in asymptomatic AAA, EVAR
is indicated for infrarenal or juxtarenal aneurysms 5.5 cm in diameter or larger [9]. There are inconsistencies among different clinical practice guidelines for AAA diameter below 5.0 cm [10]. Earlier repair is considered reasonable for AAA
sizes between 5.0 and 5.4 cm in young healthy patients. Because AAA rupture occurs at smaller diameters in women
compared to men, a lower size cutoff of ≥4.5 cm is proposed for women, but this is debatable. Accelerated expansion is
also a predictor of AAA rupture, so EVAR may be justified for an aneurysm of at least 4.0 cm in diameter if expansion
rate exceeds 0.5 cm in 6 months or 1.0 cm in 1 year. Earlier rupture occurs more commonly with saccular aneurysms compared to fusiform AAA, so while benefit is not definitively established, elective EVAR may be considered in these cases
(Table 38.1).
ANATOMIC CRITERIA FOR EVAR DEVICE ELIGIBILITY
There are several EVAR devices that are available commercially and many more are currently under investigation. Each
device has its own specific criteria for anatomic suitability for the procedure. Adherence to the instructions for use (IFU)
of the particular device is strongly recommended as off-label utilization is associated with a higher incidence of endoleaks,
stent-graft migration, and reintervention [11].
For most of the currently available EVAR devices (Table 38.2), the following requirements must be met:
1. Patent celiac trunk or superior mesenteric artery. Because the inferior mesenteric artery is essentially occluded
with EVAR, at least one of these two major branch arteries have to be intact to prevent mesenteric ischemia or
infarction.
2. A proximal landing zone of at least 10–15 mm (measured just below the ostium of the lowest renal artery to the superior
edge of the aneurysm) free from significant calcification or thrombus. This is to allow adequate seal of the stent graft
against the aortic wall.
3. A distal landing zone of at least 10–15 mm of normal common iliac segment.
TABLE 38.1 Indications for Endovascular Abdominal Aortic Aneurysm Repair
Therapeutic
Abdominal aortic aneurysm (AAA) rupture
Symptomatic AAA regardless of size
Prophylactic Against Rupture
AAA diameter >5.5 cm
Rapid AAA expansion >0.5 cm in 6 months or >1.0 cm in 1 year, if size is at least 4.0 cm
Early repair may be considered for AAA size >5.0 cm in women and young healthy men
Elective repair may be considered in patients with saccular aneurysm
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