Surveillance After Endovascular Abdominal Aortic Aneurysm Repair

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  • REVIEW

    Surveillance After Endovascular Abdominal Aortic AneurysmRepair

    Donald M. L. Tse Charles R. Tapping

    Rafiuddin Patel Robert Morgan Mark J. Bratby

    Susan Anthony Raman Uberoi

    Received: 16 August 2013 / Accepted: 3 April 2014

    Springer Science+Business Media New York and the Cardiovascular and Interventional Radiological Society of Europe (CIRSE) 2014

    Abstract Surveillance after endovascular abdominal

    aortic aneurysm repair (EVAR) is widely considered

    mandatory. The purpose of surveillance is to detect

    asymptomatic complications, so that early secondary

    intervention can prevent late aneurysm rupture. CT angi-

    ography has been taken as the reference standard imaging

    test, but there is increasing interest in using other modali-

    ties to reduce the use of ionising radiation and iodinated

    contrast. As a result, there is wide heterogeneity in sur-

    veillance strategies used among EVAR centres. We

    reviewed the current evidence available on the outcomes of

    different imaging modalities and surveillance strategies

    following EVAR.

    Keywords Endovascular procedures Surveillance Abdominal aortic aneurysm Endoleak

    Introduction

    Endovascular abdominal aortic aneurysm repair (EVAR)

    has evolved over the past two decades into an established

    alternative to open surgical repair for patients with

    abdominal aortic aneurysms. The benefits of EVAR in

    terms of the reduction in perioperative mortality compared

    with open repair have been well documented in multiple

    trials and large registries [15]. The minimally invasive

    nature of EVAR enables its application in patients with

    significant comorbidities and high operative risk. However,

    as these trials and registries also have demonstrated, the

    short-term reduction in mortality from EVAR does not

    continue into the long term, due to a higher incidence of

    late complications and a linear rate of requirement for

    secondary interventions [69]. This has resulted in the

    consensus that surveillance following EVAR is mandatory.

    On the other hand, it has been noted that only 1.49 % of

    EVAR patients undergo reintervention solely because of

    surveillance-detected abnormalities, with the majority of

    reinterventions occurring in symptomatic patients with

    previously normal surveillance studies [1012]. This

    apparent discrepancy has led to much uncertainty and a

    wide heterogeneity regarding surveillance strategies

    employed by different centres [13]. The purpose of this

    review was to evaluate the rationale and evidence behind

    surveillance strategies post EVAR.

    Purpose of Surveillance Following EVAR

    The purpose of any surveillance strategy is to identify

    asymptomatic complications so that early treatment can

    result in better long-term outcomes and prevent late

    aneurysm rupture. For the prevention of aneurysm rupture

    following EVAR, the important features to detect include

    (a) enlargement of the aneurysm sac; (b) stent-graft struc-

    tural changes, including fracture; (c) stent-graft migration

    from its deployed position; (d) stenoses or occlusions in the

    endograft limbs or outflow iliac arteries; (e) endoleaks

    where there is blood flow external to the stent-graft inside

    the aneurysm sac. Type I and III endoleaks are particularly

    important to detect, because they invariably lead to sac

    D. M. L. Tse C. R. Tapping R. Patel M. J. Bratby S. Anthony R. Uberoi (&)Department of Radiology, Oxford University Hospitals,

    John Radcliffe Hospital, Oxford OX3 9DU, UK

    e-mail: raman.uberoi@ouh.nhs.uk

    R. Morgan

    Department of Radiology, St Georges Hospital,

    Blackshaw Road, London SW17 0QT, UK

    123

    Cardiovasc Intervent Radiol

    DOI 10.1007/s00270-014-0916-z

  • expansion and aneurysm rupture and require urgent treat-

    ment after detection. Although there is a general consensus

    that only type II endoleaks associated with sac expansion

    should be treated, it is still important to detect and observe

    these endoleaks [14]. Flow-limiting stenoses in the graft

    limbs or outflow arteries are important to detect even if

    they may be asymptomatic, as they may precipitate

    thrombosis and occlusion of the graft limb.

    EVAR Surveillance Using Computed Tomography

    Since the large, randomized, controlled trials and early

    registries, computed tomography angiography (CTA) has

    been taken as the reference standard imaging test for

    EVAR surveillance. The computed tomography (CT)

    scanning protocols used by centres vary widely [15, 16],

    but all include one or more of the following phases: non-

    contrast phase to help differentiate between contrast versus

    calcification in the arterial wall, thrombus, or graft mate-

    rial; arterial contrast phase to detect endoleaks; and venous

    or delayed phase at least 60 s after contrast injection to

    identify low-flow endoleaks that may not appear in the

    arterial phase [1719].

    One main issue of a surveillance strategy using CTA is

    the use of relatively high doses of ionising radiation, which

    can range from 15 to 31 mSv per study. This can lead to

    significant cumulative risks of solid organ cancer, espe-

    cially if EVAR is performed in younger patients and sur-

    veillance continues lifelong [2022]. The repeated use of

    iodinated contrast media for CTA also raises concerns

    regarding contrast nephrotoxicity, particularly in the

    elderly or patients with renal impairment. Image quality

    with CT is degraded by streak artifacts, which can be

    caused by metallic embolisation coils or high-density

    embolic agents, such as Onyx (Covidien, Irvine, CA). This

    poses a limitation for the detection of endoleaks on CTA

    for patients who have had embolisation treatment, as part

    of the primary EVAR procedure or for subsequent endo-

    leak. Furthermore, CTA is relatively expensive compared

    with modalities, such as ultrasound. Surveillance imaging

    and secondary procedures have been shown to increase the

    overall cost of EVAR by nearly 50 %, and this impacts on

    the cost effectiveness of EVAR as a treatment option [23].

    A number of studies have aimed at reducing the radi-

    ation dose of CTA by reducing the number of scan phases

    used. Iezzi et al. [24] compared: (1) arterial phase alone,

    (2) arterial and unenhanced phase, and (3) arterial and

    delayed phases, in the detection of endoleaks after EVAR.

    They found that in addition to the arterial phase, an un-

    enhanced phase can be performed at the first follow-up

    visit, which significantly increased the specificity (from 75

    to 97 %) and positive predictive value (from 55 to 93 %)

    for detecting endoleaks in their study population of 50

    patients, who had 14 endoleaks on CT 1 month post

    EVAR (2 type I, 14 type II, 1 type III). Although the

    addition of a delayed phase scan increased the detection of

    low-flow endoleaks, this did not reach statistical signifi-

    cance. Macari et al. [25] studied 110 CT examinations in

    85 patients and found that the 3 type I and 1 type III

    endoleaks were identified in both arterial and venous

    phases, but 3 of 28 type II endoleaks were only seen in the

    venous phase, and led the authors to conclude that the

    arterial phase can be omitted to reduce radiation dose.

    Bastos et al. [26] came to a similar conclusion in their

    study of 30 patients who underwent CTA and found that 3

    of 8 type II endoleaks were not visible in the arterial

    phase scans but were all visible in the venous phase (there

    were no type I or type III endoleaks in this series).

    However, the clinical significance of the endoleaks

    detected only in the venous phases in these studies was

    not known. In the study by Hong et al., in 144 patients

    with endoleaks, 8 of the endoleaks were detected in the

    delayed phase only but these all resolved spontaneously,

    suggesting that these low-flow endoleaks may not have

    clinical significance. The authors concluded that the

    delayed phase can be omitted from surveillance CT scans

    [27]. These studies are summarised in Table 1.

    Other researchers have investigated whether noncontrast

    CT scans can provide adequate information for surveil-

    lance after EVAR and obviate the need for contrast media.

    In the study by Bley et al. [28] of 70 patients, aortic volume

    analysis was performed on noncontrast images, and they

    found that in 10 type I or III endoleaks showed a mean

    10 % increase in aortic volume, whereas 37 type II en-

    doleaks showed a mean 5.4 % increase in aortic volume.

    The authors concluded that noncontrast CT with aortic

    volume analysis can be used for surveillance, and contrast-

    enhanced imaging only performed if there is an aortic

    volume increase of more than 2 %.

    Magnetic Resonance Imaging/Angiography

    Magnetic resonance imaging (MRI) and gadolinium-

    enhanced angiography provide an alternative imaging

    modality to CTA, with the obvious advantage being the

    avoidance of ionising radiation. Several different imaging

    protocols for MRI have been investigated. The majority of

    data on the use of magnetic resonance imaging/angiogra-

    phy (MRI/MRA) for surveillance post EVAR involves

    three-dimensional, gadolinium-enhanced dynamic and

    delayed MRA. More recently, time-resolved MRA has

    been used to provide information on the direction of flow

    of contrast medium post EVAR [2931]. Both extracellular

    and blood-pool contrast agents have been used successfully

    D. M. L. Tse et al.: Surveillance After EVAR

    123

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    D. M. L. Tse et al.: Surveillance After EVAR

    123

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    D. M. L. Tse et al.: Surveillance After EVAR

    123

  • to image endoleaks, with blood pool agents suggested to

    improve the detection of slow flow endoleaks [29, 30, 32].

    MRI is limited by cost and availability and is contra-

    indicated in patients with pacemakers or claustrophobic

    patients. The extensive susceptibility artefacts seen with

    stainless steel also mean that MRI has a very limited role in

    the imaging of patients with grafts containing stainless

    steel (e.g., Zenith Flex device; Cook, Bloomington, IN), as

    opposed to nitinol-based grafts, which produce less arte-

    fact. Moreover, as stainless steel embolization coils also

    produce MR artefact, MRI is not a good modality for the

    follow-up of patients who have undergone coil emboliza-

    tion of the internal iliac artery before EVAR. Patients with

    chronic kidney disease (CKD) stage 4 or 5 (GFR\30 mL/min) are at high risk of developing nephrogenic systemic

    fibrosis (NSF) after gadolinium administration, and there-

    fore the use of gadolinium-based contrast agents in these

    patients is contraindicated, whereas its use should be with

    caution in patients with CKD stage 3 (GFR 3059 mL/min)

    who are at lower risk of developing NSF [33].

    MRA has been shown to be comparable to CT for the

    measurement of the aortic diameter and thus the sac size

    [34]. For the detection of endoleaks, MRI has been eval-

    uated against CTA in several studies, 11 of which were

    included in a recent systematic review, totalling 369

    patients and 562 pairs of MRI and CTA examinations [30,

    3444]. These studies are summarised in Table 2. Overall,

    MRI detected 132 additional endoleaks compared with

    CTA, including 86 type II (187 for MRI vs. 101 for CTA)

    and 26 indeterminate (39 for MRI vs. 13 for CTA) en-

    doleaks. MRA missed 2 of 15 type I endoleaks detected on

    CTA. In one of these cases, a type Ib endoleak was masked

    by vessel wall calcification and the platinum markers of a

    distal limb, whereas in the other case, consensus reading of

    CTA and MRA between two readers concluded no type I

    endoleak [37, 38]. Twelve additional cases of type III en-

    doleaks were detected on MRI. In 1 case, the additional

    type III endoleak was classified as type II on subsequent

    catheter angiography [36]; among the other 11 cases

    reported by Pitton et al. [37], only 1 resulted in secondary

    treatment, and it was unclear why the other cases were not

    treated, as currently all type III endoleaks require treat-

    ment. Similarly, because information on aneurysm growth

    was not available, it is not clear how many of the additional

    type II endoleaks were clinically significant.

    There is difficulty in assessing device integrity with

    MRI, which limits its use as a sole modality for surveil-

    lance, and to date no published studies have evaluated the

    clinical outcomes of an MRI-based surveillance protocol.

    However, the added sensitivity for endoleaks from MRI

    means that it can be a useful complementary test, partic-

    ularly in cases where endoleak is suspected due to aneu-

    rysm growth, but not demonstrable on CTA.

    Duplex Ultrasound and Contrast-Enhanced Ultrasound

    There is considerable interest in the use of duplex ultrasound

    (DUS) and contrast-enhanced ultrasound (CEUS) as alterna-

    tives to CTA. There are obvious benefits of ultrasound, which

    uses no ionising radiation and no nephrotoxic contrast agents,

    and allows dynamic examination of the areas of interest. DUS

    allows an assessment of the direction and velocity of flow, is

    widely available, and is less expensive than CTA. Regarding

    CEUS, after the intravenous injection of contrast microbub-

    bles, the appearance of the contrast medium can be followed in

    real-time as it appears within the graft and any endoleak can be

    visualised as contrast outside the graft in the aneurysm sac.

    This provides a dynamic assessment of the endoleak, which

    enables the radiologist to identify the site of origin of the

    endoleak and therefore define the endoleak type. Because the

    contrast microbubbles can persist in the blood pool for some

    time, the ultrasound assessment can extend into the delayed

    phase continuously. The disadvantages of using ultrasound

    include operator dependence and the variability in image

    quality depending on patient body habitus. The use of contrast

    agents also adds to the cost of the examination, although

    CEUS is reported to still be cheaper than CTA [45].

    In a meta-analysis by Karthikesalingam et al., including 25

    studies comparing DUS, CEUS against CT for EVAR sur-

    veillance, the pooled sensitivities for all endoleaks were 0.74

    for DUS and 0.96 for CEUS and pooled specificities were 0.94

    for DUS and 0.85 for CEUS. However, when comparing

    ultrasound against CTA for only types I and III endoleaks,

    features that alone would be sufficient to necessitate reinter-

    vention, the pooled sensitivities were 0.83 for DUS and 0.99

    for CEUS, and pooled specificities were 1.00 for both DUS

    and CEUS [46]. The results suggest that the added benefit of

    CEUS over DUS would be in diagnosing type II endoleaks,

    which unless there is sac enlargement, do not require rein-

    tervention. Meanwhile, there is good correlation between US

    and CT for the measurement of aneurysm sac size, and

    although US may consistently underestimate sac diameter

    compared with CT, for individual patients it is the change in

    sac size that is most relevant [4750]. Therefore, aneurysm sac

    enlargement could be detected by DUS alone and direct fur-

    ther investigation with CEUS or CTA. Meanwhile, asymp-

    tomatic type II endoleaks without sac enlargement may be

    missed by DUS. However, type II endoleaks generally do not

    require intervention. Studies evaluating surveillance strate-

    gies using DUS and/or CEUS are summarised in Table 3 and

    discussed below.

    Plain Radiography

    The main role of plain radiographs is to assess the structural

    integrity and detect limb kinks or endograft migration. Plain

    D. M. L. Tse et al.: Surveillance After EVAR

    123

  • Ta

    ble

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    D. M. L. Tse et al.: Surveillance After EVAR

    123

  • radiography has no role in the assessment of aneurysm sac size

    and endoleak detection. Plain radiographs, when taken using

    consistent centring protocols, such as the Liverpool/Perth

    protocol, allow reliable detection of kinks and migration of the

    stent graft down to within 2 mm, at a fraction of the dose of CT

    [32, 5153]. However, plain radiographs cannot be used as a

    sole surveillance modality and must be combined with a

    modality, such as US, which can detect endoleaks and sac size

    enlargement.

    The complementary role of the abdominal radiograph

    (AXR) was reported by Harrison et al., which used annual

    AXR and DUS as the primary surveillance studies, with CTA

    performed only when there are significant findings on AXR or

    DUS, or if views of the aneurysm were unsatisfactory on DUS

    [54]. In 194 patients undergoing a median of 36 months of

    follow-up, AXR showed migration in 16 cases. Fifteen of the

    patients were investigated by CTA and migration was con-

    firmed in 10 patients, giving a positive predictive value (PPV)

    for AXR of 67 %. This protocol of AXR and DUS for follow-

    up reduced the use of CTA by 83, and 65 % of patients did not

    require any CTA at 4 years [54]. In another study, Dias et al.

    showed in 279 patients undergoing annual CT following

    EVAR that only 26 (9.3 %) of the patients benefited from CT

    surveillance and required reinterventions based on asymp-

    tomatic findings. Of these 26 patients, only 1 patient, who had

    partial coverage of the superior mesenteric artery and mal-

    perfusion, would not have been detected by AXR and simple

    diameter measurements using US [11]. These findings led to

    their conclusion that CT is not required for the follow-up of the

    majority of patients but should be used as a problem solver

    when DUS or AXR suggest a problem.

    Digital Subtraction Angiography

    Digital subtraction angiography (DSA) has a no role in the

    routine surveillance of patients following EVAR, given its

    invasive nature and availability of other highly sensitive

    imaging tests. However, DSA allows demonstration of contrast

    flow direction and therefore is more helpful than CTA for the

    classification of endoleaks in selected patients, where there is a

    question regarding the type of endoleak type on CTA. There-

    fore, the current role of DSA is as a problem solver to (a) define

    the type of endoleak where there is uncertainty on noninvasive

    imaging, and (b) as a final imaging modality to detect and treat

    an endoleak when there is an enlarging aneurysm sac and no

    visible endoleak on noninvasive imaging, including CEUS.

    Aneurysm Sac Pressure Measurement

    As an alternative to using imaging techniques, measure-

    ment of the aneurysm sac pressure provides physiological

    information about the repaired aneurysm [55]. Direct

    pressure measurement by percutaneous sac puncture has

    been reported by Dias et al. [56] in the follow-up of 37

    patients, which showed that high sac pressure was associ-

    ated with sac expansion, whereas low sac pressure was

    associated with shrinkage. Successful endoleak embolisa-

    tion in four patients resulted in pressure reduction. Non-

    invasive pressure measurement involves the use of wireless

    sensors, which can be implanted into the aneurysm sac at

    the time of EVAR. Okhi et al. [57] showed in a multicentre

    trial of 76 patients the safety profile of a wireless pressure

    sensor, and demonstrated a sensitivity of 0.94 and speci-

    ficity of 0.80 for the detection of type I or III endoleaks.

    Ellozy et al. [58] showed in 21 patients who underwent

    EVAR with an implantable remote pressure sensor that the

    sac pressure was significantly lower in patients who have

    aneurysm sac shrinkage compared with those with no

    aneurysm shrinkage. However, despite early promising

    results pressure measurements for EVAR surveillance its

    use has not become widespread. Limitations including the

    lack of information on graft structural integrity or graft

    migration, and the lack of long-term follow-up data.

    Can We Move Away From CT to US Plus AXR

    for Surveillance?

    Several groups have reported on the use of DUS alone for

    surveillance and reserving CTA for only patients with

    abnormal or inadequate US. These data are summarised in

    Table 3. Collins et al. reported a 5-year retrospective

    review of 160 patients who underwent DUS surveillance,

    with CTA performed in the event of aneurysm sac

    enlargement or endoleak on DUS. Forty-one endoleaks

    were identified out of 359 DUS exams in these patients; in

    35 cases investigated on subsequent CTA, 14 were con-

    firmed. In three cases CTA demonstrated endoleaks that

    were not detected on DUS, and in all three cases DUS

    demonstrated sac enlargement; however, none of these

    three endoleaks required additional intervention [59].

    Chaer et al. [60] initially moved to a surveillance protocol

    of using DUS alone from as early as 1 year post-EVAR, for

    patients with a collapsed aneurysm sac. Subsequently they

    expanded the use of DUS alone for surveillance in patients

    with any sac shrinkage by C5 mm or stable size over

    2 years. In their cohort of 184 patients with an average

    DUS-only follow-up of 24 months, 3 endoleaks were

    detected, including 2 type I endoleaks, which required limb

    extensions, and 1 type II endoleak, which did not require

    treatment. There were no adverse events, ruptures, device

    failures, or limb occlusions observed as a consequence of

    the DUS alone protocol [60]. Beeman et al. [48] converted

    from a combined CTA and DUS surveillance protocol to

    D. M. L. Tse et al.: Surveillance After EVAR

    123

  • Ta

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    D. M. L. Tse et al.: Surveillance After EVAR

    123

  • using DUS only, with additional imaging only if a problem

    was detected. In 117 patients who underwent the DUS only

    surveillance for average of 1.6 years, 29 patients (25 %)

    had an endoleak detected, although only 3 required sec-

    ondary intervention. There were no adverse events, such as

    rupture, graft migration, or limb occlusion, observed as a

    consequence of this change of strategy [48]. It was sug-

    gested that using DUS alone led to cost savings of $1,595

    per patient per year in their cohort [48].

    To date, there have been no studies evaluating surveil-

    lance protocols using CEUS alone or in combination with

    AXR to replace CTA surveillance. In a recent study of 539

    patients by Millen et al., the surveillance protocol consisted

    of the following: CTA at 1 month, followed by annual

    AXR and DUS, with further CTA only if AXR or DUS

    showed abnormality or inconclusive results; CEUS was

    used when there were discordant or nondiagnostic findings

    (including the identification of endoleak type, and signifi-

    cant sac expansion without identifiable endoleak) [45]. Of

    27 patients who had an endoleak of indeterminate type,

    CEUS demonstrated 4 to be type I (all confirmed at sec-

    ondary intervention); 21 endoleaks were demonstrated to

    be type II (5 of the 21 cases went on to secondary inter-

    vention and were confirmed as type II); in 2 cases CEUS

    excluded an endoleak but in 1 of these 2 patients, a type II

    endoleak was found on subsequent follow-up. Four patients

    in this study had sac enlargement with no endoleak dem-

    onstrated on DUS or CTA. CEUS demonstrated one type II

    endoleak confirmed at secondary treatment; in the other

    three patients no endoleak was detected, although in one

    patient a small type II endoleak was shown on subsequent

    follow-up (Table 4). The authors suggested that CEUS can

    be used to complement EVAR surveillance when other

    imaging modalities are nondiagnostic.

    Timing and Duration of Surveillance

    Most complications and secondary interventions, including

    ruptures, occur within the first 2-3 years following EVAR

    [61, 62]. As a result, most surveillance protocols involve

    early surveillance at most if not all of the following time

    points: at discharge, 1, 3, 6, 12 months, with subsequent

    annual follow-up after [61, 62].

    Several studies have investigated the value of surveil-

    lance at certain time points; these are summarised in

    Table 4. In the study by Waasdorp et al., CT was per-

    formed postprocedure and at 3 months. It was found that in

    287 of 291 patients, the postprocedural CT performed

    before discharge did not influence the treatment policy in

    the first 3 months after EVAR and led the authors to

    conclude that the predischarge postprocedural CT scan can

    be omitted after an uneventful EVAR procedure [63].

    However, in their cohort, four patients required early sec-

    ondary interventions based on predischarge CTA findings,

    including two type I and one type III endoleaks, which

    required extension or interposition cuffs, and coiling of a

    type II endoleak [63].

    The utility of the surveillance CT at 6 months was

    challenged in the study by Go et al. [64], which demon-

    strated that in 130 patients with a normal CTA at 1 month,

    no clinically significant findings warranting intervention

    were identified at 6 months, with only two type II en-

    doleaks without sac enlargement. Incidentally only 1 of the

    130 patients had an abnormal CTA at 1 year that required

    intervention. The omission of the surveillance at 6 months

    for low-risk patients also was reported in the 5-year follow-

    up study in the US Zenith multicentre trial, which included

    739 patients [65]. Indeed, surveillance at 6 months was not

    a requirement for the recent ENGAGE registry of the En-

    durant stent graft (Medtronic, Santa Rosa, CA) [66].

    While reducing the frequency and type of early sur-

    veillance studies has been studied in some detail, there is

    relatively little data or enthusiasm regarding the cessation

    of long-term imaging surveillance post EVAR. The paucity

    of very long-term (10?) years follow-up data for EVAR,

    especially for the newer generation of stent grafts, and the

    knowledge that at least up to 8 years there is still a linear

    rate for reinterventions means that for most patients the

    safest option would still be to continue surveillance [62].

    However, Nordon et al. [62] have proposed that patients

    who complete 3 years of surveillance without detection of

    endoleak or sac enlargement can be discharged from fol-

    low-up. Indeed, in a recently published survey of surveil-

    lance practice in the U.K., most centres would continue

    surveillance indefinitely annually, with some reducing the

    frequency to biannually but seemingly without much evi-

    dence-base [15].

    Risk Stratification for Surveillance

    In the large, clinical trials and registries of EVAR, the

    follow-up protocols are mostly uniform throughout. How-

    ever, in routine clinical practice, the spectrum of patients

    being treated is much wider and clearly a one size fits all

    surveillance strategy would likely result in over-investi-

    gation of low-risk patients and reduce the cost-effective-

    ness of an EVAR programme. It is known that hostile neck

    anatomy represents an independent risk factor for early and

    late complications after EVAR [6771]. In an evaluation of

    the Endurant stent graft (Medtronic) comparing patients

    treated according to device-specific instructions for use

    (IFU) against off-label use with unfavourable proximal

    neck anatomy, there was a significant increase in type I

    endoleak at 1 year in the off-label use group [72]. An

    D. M. L. Tse et al.: Surveillance After EVAR

    123

  • association between larger aneurysm size and an increased

    rupture risk after EVAR also has been seen in several trials

    [61]. These known risk factors suggest that it is possible to

    risk stratify patients for the risk of complications and target

    more intensive surveillance regimes to the high-risk

    patients only.

    The use of an initial surveillance imaging test to risk

    stratify patients also has been explored; the aim is to

    stratify patients into those at a high risk of complications

    and therefore justifying a more intensive protocol closer to

    the traditional CT-based surveillance schedule, and those at

    a low risk of complications where less frequent surveil-

    lance and the use of DUS should be considered. These

    studies are summarised in Table 4.

    The use of the initial predischarge CTA to stratify

    patients into high- or low-risk groups was investigated by

    Goncalves et al. in a cohort of 131 patients with 4.1 years

    follow-up. Patients were categorised as high risk if on the

    predischarge CTA there was a proximal or distal seal

    length of\10 mm, or if there was an endoleak; otherwise,they were categorised as low risk [73]. Of 62 low-risk

    patients, only 3 patients required secondary interventions,

    whereas 23 of 69 high-risk patients required secondary

    interventions. Freedom from aneurysm-related adverse

    events at 5 years was 98 % for the low-risk group and

    52 % for the high-risk group [73]. These results led the

    authors to conclude that surveillance in low-risk patients

    can be substantially reduced. The findings from this paper

    Fig. 1 Proposed EVARsurveillance pathway

    D. M. L. Tse et al.: Surveillance After EVAR

    123

  • are echoed by Patel and Carpenter who showed in their

    cohort of 345 patients that the initial postoperative CT was

    negative for endoleak in 247 patients, and only 9 of 247

    received subsequent secondary procedures, giving a nega-

    tive predictive value for freedom from secondary inter-

    vention of 96.4 %; the authors suggested that with DUS

    surveillance after initial CT to detect sac size expansion,

    the negative predictive value of follow-up can be improved

    to 97.6 % [74].

    In the European Society for Vascular Surgery (ESVS)

    2010 guidelines for the management of abdominal aortic

    aneurysms, following EVAR, the 1-month CTA and AXR

    should be used to dichotomise patients into those with and

    without endoleak. Patients without an endoleak should

    undergo one further CTA at 12 months and DUS ? AXR

    thereafter. Patients with a type II endoleak should undergo

    CTA at 6 and 12 months and annual CT and AXR thereafter

    [14].

    Conclusions

    There is a need to improve current surveillance strategies to

    reduce radiation dose, cost, and maintain quality of life for

    patients with a minimal risk of secondary complications

    particularly aneurysm-related rupture. Just as EVAR stent

    graft technology continues to evolve, strategies for sur-

    veillance after EVAR also are undergoing continuous

    refinement and will be expected to do so for the foreseeable

    future as more data accrues.

    We propose a surveillance strategy based on the above

    evidence (Fig. 1). Risk stratification is implemented

    throughout the strategy to reduce the use of CTA, and thus

    ionising radiation and iodinated contrast. DUS in combi-

    nation with AXR replaces CTA for low-risk patients, based

    on the findings of previous studies summarised in Table 3,

    which have demonstrated the sensitivity DUS and AXR for

    type I and III endoleaks, or sac enlargement, which can

    then trigger further investigation with CTA. The very high

    sensitivity demonstrated in meta-analyses of CEUS and

    MRA compared with CTA means that CEUS or MRA may

    be used as a replacement for CTA in selected patients [30,

    46]. Risk stratification occurs at multiple points:

    (a) immediately postprocedure where a larger aneurysm or

    unfavourable anatomy places the patient in higher risk of

    complications, as described by Torsello et al. [72]; (b) after

    predischarge CTA in high-risk patients, based on findings

    by Goncalves et al. and Carpenter et al. [73, 74]; (c) after

    1 year, at which point patients are stratified into low and

    high risk with potential for transition between the two

    groups based on subsequent follow-up findings, as sup-

    ported by the studies investigating DUS, and the ESVS

    2010 guidelines [14]. In terms of timing of surveillance

    studies, predischarge imaging allows the detection of type I

    and III endoleaks, which require immediate treatment, and

    risk stratification for subsequent follow-up; surveillance

    study at 6 months is eliminated based on lack of utility as

    demonstrated by Go et al. [64]; the discharge of low-risk

    patients from lifelong surveillance, while not widely

    practised, has been suggested in this strategy.

    Finally, it is evident that the precise surveillance strat-

    egy employed by each unit is likely to vary due to differ-

    ences in the choice of stent-graft, local expertise and

    experience, financial constraints, and availability of DUS

    and CEUS services until compelling data are available that

    will mandate a universal approach to surveillance after

    EVAR.

    Conflict of interest Donald M.L. Tse, Charles R. Tapping, Raf-iuddin Patel, Robert Morgan, Mark J. Bratby, Susan Anthony, Raman

    Uberoi have no conflict of interest.

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    Surveillance After Endovascular Abdominal Aortic Aneurysm RepairAbstractIntroductionPurpose of Surveillance Following EVAREVAR Surveillance Using Computed TomographyMagnetic Resonance Imaging/AngiographyDuplex Ultrasound and Contrast-Enhanced UltrasoundPlain RadiographyDigital Subtraction AngiographyAneurysm Sac Pressure MeasurementCan We Move Away From CT to US Plus AXR for Surveillance?Timing and Duration of SurveillanceRisk Stratification for SurveillanceConclusionsReferences

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