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Editor's Choice – A Comparison of Computed Tomography Angiography and Colour Duplex Ultrasound Surveillance Post Infrarenal Endovascular Aortic Aneurysm Repair: Financial Implications and Impact of Different International Surveillance Guidelines

Open ArchivePublished:June 14, 2021DOI:https://doi.org/10.1016/j.ejvs.2021.04.005

      Objective

      Use of colour duplex ultrasound (CDUS) and computed tomography angiography (CTA) for infrarenal endovascular aortic aneurysm repair (EVAR) surveillance differs in internationally published guidelines. This study aimed firstly to compare CDUS detection of significant sac abnormalities with CTA. Secondly, a sensitivity analysis was conducted to compare financial estimates of the, predominantly CDUS based, local and Society of Vascular Surgery (SVS) protocols, the risk stratified European Society of Vascular Surgery (ESVS) protocol, and the CTA based National Institute of Health and Care Excellence (NICE) protocol.

      Methods

      Agreement between CDUS and CTA was assessed for detection of significant sac abnormalities. Surveillance protocols were extrapolated from published guidelines and applied to infrarenal EVAR patients active on local surveillance at a large, single centre. Surveillance intensity was dependent on presence of endoleak and subsequent risk of treatment failure in accordance with surveillance recommendations. Estimates for each surveillance protocol were inclusive of a range of published incidences of endoleak, contrast associated acute kidney injury (AKI), and excess hospital bed days, and estimated for a hypothetical five year surveillance period.

      Results

      The kappa coefficient between CDUS and CTA for detecting sac abnormalities was 0.68. Maximum five year surveillance cost estimates for the 289 active EVAR patients were £272 359 for SVS, £230 708 for ESVS, £643 802 for NICE, and £266 777 for local protocols, or £1 270, £1 076, £3 003, and £1 244 per patient. Differences in endoleak incidence accounted for a 1.1 to 1.4 fold increase in costs. AKI incidence accounted for a 3.3 to 6.2 fold increase in costs.

      Conclusion

      A combined CTA and CDUS EVAR surveillance protocol, with CTA reserved for early seal assessment and confirmatory purposes, provides an economical approach without compromising detection of sac abnormalities. AKI, as opposed to direct imaging costs, accounted for the largest differences in surveillance cost estimates.

      Keywords

      The Society of Vascular Surgery (SVS), European Society of Vascular Surgery (ESVS), and National Institute for Health Care and Excellence (NICE) guidelines, and a local surveillance protocol were compared using a sensitivity analysis to estimate the financial implications post infrarenal endovascular aortic aneurysm repair. Variations in published incidences of endoleak, acute kidney injury (AKI), and excess bed days were factored in estimates. Large increases in costs were associated with preferential use of computed tomography angiography (CTA) primarily because of the inclusion of AKI. Reserving CTA for early seal assessment and confirmatory purposes, reduces costs without compromising patient safety.

      Introduction

      Infrarenal endovascular aortic aneurysm repair (EVAR) is widely used to treat patients with both unruptured and ruptured abdominal aortic aneurysms (AAA) below the level of the renal arteries. However, complications such as endoleaks, limb kinking, and device migration are common.
      • White G.H.
      • Yu W.
      • May J.
      • Chaufour X.
      • Stephen M.S.
      Endoleak as a complication of endoluminal grafting of abdominal aortic aneurysm: classification, incidence, diagnosis and management.
      • Nordon I.M.
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      • Holt P.J.
      • Loftus I.M.
      • Thompson M.M.
      Secondary interventions following endovascular aneurysm repair (EVAR) and the enduring value of graft surveillance.
      • Chaikof E.L.
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      • Eskandari M.K.
      • Jackson B.M.
      • Lee W.A.
      • Ashraf M.
      • et al.
      The Society of Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm.
      Endoleak incidence varies by type, and ranges from 4% to 10% for type 1 and 3 endoleaks
      • Quinn A.A.
      • Mehta M.
      • Teymouri M.J.
      • Keenan N.
      • Paty P.S.K.
      • Zhou Y.
      • et al.
      The incidence and fate of endoleaks vary between ruptured and elective endovascular abdominal aortic aneurysm repair.
      ,
      • Verzini F.
      • Romano L.
      • Parlani G.
      • Isernia G.
      • Simonte G.
      • Loschi D.
      • et al.
      Fourteen-year outcomes of abdominal aortic aneurysm endovascular repair with the Zenith stent graft.
      and 10% to 27% for type 2 endoleaks.
      • Verzini F.
      • Romano L.
      • Parlani G.
      • Isernia G.
      • Simonte G.
      • Loschi D.
      • et al.
      Fourteen-year outcomes of abdominal aortic aneurysm endovascular repair with the Zenith stent graft.
      • Guo Q.
      • Du X.
      • Zhao J.
      • Ma Y.
      • Huang B.
      • Yuan D.
      • et al.
      Prevalence and risk factors of type II endoleaks after endovascular aneurysm repair: A meta-analysis.
      • Sidloff D.A.
      • Stather P.W.
      • Choke E.
      • Bown M.J.
      • Sayers R.D.
      Type II endoleak after endovascular aneurysm repair.
      Lifelong imaging surveillance is mandated in internationally published guidelines
      • Chaikof E.L.
      • Dalman R.L.
      • Eskandari M.K.
      • Jackson B.M.
      • Lee W.A.
      • Ashraf M.
      • et al.
      The Society of Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm.
      ,
      • Wanhainen A.
      • Verzini F.
      • van Herzeele I.
      • Allaire E.
      • Bown M.
      • Cohnert T.
      • et al.
      European Society for Vascular Surgery (ESVS) 2019 Clinical practice guidelines on the management of abdominal aorto-iliac artery aneurysms.
      ,

      National Institute for Health and Care Excellence (NICE). Abdominal aortic aneurysm: diagnosis and management (NICE guideline [NG156]). Available from https://www.nice.org.uk/guidance/ng156. [Accessed 20 Mar 2020].

      to detect abnormalities with the aim of mitigating sac re-pressurisation; however, recommendations vary.
      Computed tomography angiography (CTA) is traditionally considered the gold standard for endoleak detection; however, colour duplex ultrasound (CDUS) is used widely, with good agreement reported between modalities.
      • Baderkhan H.
      • Wanhainen H.
      • Haller O.
      • Björk M.
      • Mani K.
      Detection of late complications after endovascular abdominal aortic aneurysm repair and implications for follow up based on retrospective assessment of a two centre cohort.
      The North American Society of Vascular Surgery (SVS) guidelines
      • Chaikof E.L.
      • Dalman R.L.
      • Eskandari M.K.
      • Jackson B.M.
      • Lee W.A.
      • Ashraf M.
      • et al.
      The Society of Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm.
      recommend annual CDUS surveillance as a minimum requirement following EVAR, whereas the frequency of scans in the European Society of Vascular Surgery (ESVS) guidelines
      • Wanhainen A.
      • Verzini F.
      • van Herzeele I.
      • Allaire E.
      • Bown M.
      • Cohnert T.
      • et al.
      European Society for Vascular Surgery (ESVS) 2019 Clinical practice guidelines on the management of abdominal aorto-iliac artery aneurysms.
      is stratified according to risk of device or treatment failure. The recently published National Institute for Health and Care Excellence (NICE) guidelines

      National Institute for Health and Care Excellence (NICE). Abdominal aortic aneurysm: diagnosis and management (NICE guideline [NG156]). Available from https://www.nice.org.uk/guidance/ng156. [Accessed 20 Mar 2020].

      in the UK concluded that the absence of endoleak detection on CDUS was insufficient to confirm exclusion, and therefore annual CTA assessment is required.
      CTA is associated with increased surveillance costs, risk of malignancy,
      International Commission on Radiological Protection (ICRP)
      Avoidance of Radiation Injuries from Medical Interventional Procedures. ICRP Publication 85.
      and contrast induced nephropathy (CIN).
      • Saratzis A.N.
      • Goodyear S.
      • Sur H.
      • Saedon M.
      • Imray C.
      • Mahmood A.
      Acute kidney injury after endovascular repair of abdominal aortic aneurysm.
      CIN resulting in acute kidney injury (AKI) is reported in 2% – 5% of cases,
      • Lee J.
      • Cho J.Y.
      • Lee H.J.
      • Jeong Y.Y.
      • Kim C.K.
      • Park B.K.
      • et al.
      Contrast-induced nephropathy in patients undergoing intravenous contrast-enhanced computed tomography in Korea: a multi-institutional study in 101487 patients.
      • Mitchell A.M.
      • Jones A.E.
      • Tumlin J.A.
      • Kline J.A.
      Incidence of contrast-induced nephropathy after contrast-enhanced computed tomography in the outpatient setting.
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      with 0.5% – 1% requiring renal replacement therapy (RRT).
      • Rudnick M.
      • Feldman H.
      Contrast-induced nephropathy: what are the true clinical consequences?.
      ,
      • Moos S.I.
      • van Vemde D.N.H.
      • Stoker J.
      • Bipat S.
      Contrast induced nephropathy in patients undergoing intravenous (IV) contrast enhanced computed tomography (CECT) and the relationship with risk factors: a meta-analysis.
      Treatment for AKI is associated with further costs, resources, and prolonged hospital stay.
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      ,
      • Rudnick M.
      • Feldman H.
      Contrast-induced nephropathy: what are the true clinical consequences?.
      Reserving CTA for confirmatory purposes following CDUS abnormality detection may be a preferable alternative.
      This study firstly describes experience of a predominantly CDUS surveillance programme in a large, single centre with respect to protocol and performance of directing post EVAR re-interventions. Secondly, attempts were made to estimate the five year financial implications of the SVS, ESVS, and NICE surveillance guidelines, and local surveillance protocols, post infrarenal EVAR using a multivariable sensitivity analysis, taking into consideration variations in the published incidences of endoleaks, AKI, and excess hospital days.

      Methods

      Imaging modality comparison

      All patients that underwent an infrarenal EVAR procedure at the study centre were identified retrospectively from a prospectively maintained surveillance database. The current surveillance protocol (Fig. 1) was established in 2007, prior to which all EVARs underwent annual CTA surveillance for between two and four years before transferring to CDUS surveillance. EVARs performed pre-2007, and those with isolated iliac aneurysms and complex EVARs, including fenestrated, thoracoabdominal, or endovascular sealing devices (e.g. Nellix), were excluded. All CTA images were reviewed by a vascular surgeon or interventional radiologist. All CDUS assessments were performed and reported by experienced clinical vascular scientists. Follow up data obtained included: CTA confirmation of early aneurysm seal (defined as apposition to a non-diseased aortic wall for at least 10 – 15 mm), sac abnormalities, re-interventions, and rupture rates.
      Figure 1
      Figure 1Local post infrarenal endovascular aortic aneurysm repair (EVAR) surveillance protocol. CTA = computed tomography angiography; CDUS = colour duplex ultrasound.
      The kappa coefficient of agreement was calculated for CDUS and CTA scans occurring within a four week window over a five year period (2012–2017). Agreement was assessed for detection of significant sac abnormality (defined as absence of any endoleak or sac expansion ≥ 5 mm).

      Endovascular aortic aneurysm repair surveillance financial sensitivity analysis

      Predicted costs of the SVS, ESVS, NICE and local surveillance protocols were compared over a five year period by constructing a hypothetical model and multivariable sensitivity analysis using estimates published in large population studies. The model was constructed with three patient risk categories based on potential for EVAR failure: low, intermediate, and high, depending on endoleak status (Table 1). Differences in surveillance protocol for each risk category are described in Table 2, according to the corresponding recommendations.
      Table 1Definitions of patient risk categories included in hypothetical model to estimate the five year costs of the Society of Vascular Surgery (SVS), European Society of Vascular Surgery (ESVS), National Institute of Health and Care Excellence (NICE) and local surveillance protocols post infrarenal endovascular aortic aneurysm repair
      Patient risk categoryClinical detailsAssumptions
      LowNo endoleak detected throughout surveillanceNone
      IntermediateType 2 endoleak detected in first yearEndoleak resolves spontaneously; does not require re-intervention
      HighType 1 or 3 endoleak detected in first yearEndoleak successfully treated; does not recur during surveillance
      Table 2Society of Vascular Surgery (SVS), European Surgery of Vascular Surgery (ESVS), and National Institute of Health and Care Excellence (NICE) surveillance guidelines for patients with low, intermediate, and high risk of infrarenal endovascular aortic aneurysm repair (EVAR) device failure
      ProtocolRisk of EVAR device failure
      Low, no endoleakIntermediate, type 2 endoleakHigh, type 1 or 3 endoleak,
      SVS
      • Chaikof E.L.
      • Dalman R.L.
      • Eskandari M.K.
      • Jackson B.M.
      • Lee W.A.
      • Ashraf M.
      • et al.
      The Society of Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm.
      1 mo CTA, annual CDUS if no type 1 or 3 endoleak or sac expansion (CTA if CDUS unavailable); 5 y CTAType 2 endoleak – 6mo surveillance for 24 mo; annual CDUSConfirmatory CTA if abnormal CDUS findings – evaluate for re-intervention
      ESVS
      • Verzini F.
      • Romano L.
      • Parlani G.
      • Isernia G.
      • Simonte G.
      • Loschi D.
      • et al.
      Fourteen-year outcomes of abdominal aortic aneurysm endovascular repair with the Zenith stent graft.
      1 mo CTA – if adequate seal CTA at 5 yType 2 endoleak – annual CDUS for sac diameter; postpone surveillance if sac shrinkage ≥ 1 cmFurther imaging to evaluate for re-intervention if type 1 or 3 endoleak
      NICE
      • Guo Q.
      • Du X.
      • Zhao J.
      • Ma Y.
      • Huang B.
      • Yuan D.
      • et al.
      Prevalence and risk factors of type II endoleaks after endovascular aneurysm repair: A meta-analysis.
      1 mo CTA; annual CTA to detect endoleak (CDUS can be used for sac diameter but not to exclude endoleak)Not explicitly specified – evaluate for re-intervention if type 2 endoleak with sac expansionNot explicitly specified – evaluate for re-intervention
      CTA = computed tomography angiography; CDUS = colour duplex ultrasound.
      Cost estimates factored differences in incidence of endoleaks, CIN resulting in AKI and RRT, and subsequent extension of hospital stay. Sensitivity analysis was used to factor the uncertainty and variation of observed endoleak and AKI rates, and included three categories with differing published incidences, A, B, and C for endoleak
      • Quinn A.A.
      • Mehta M.
      • Teymouri M.J.
      • Keenan N.
      • Paty P.S.K.
      • Zhou Y.
      • et al.
      The incidence and fate of endoleaks vary between ruptured and elective endovascular abdominal aortic aneurysm repair.
      • Verzini F.
      • Romano L.
      • Parlani G.
      • Isernia G.
      • Simonte G.
      • Loschi D.
      • et al.
      Fourteen-year outcomes of abdominal aortic aneurysm endovascular repair with the Zenith stent graft.
      • Guo Q.
      • Du X.
      • Zhao J.
      • Ma Y.
      • Huang B.
      • Yuan D.
      • et al.
      Prevalence and risk factors of type II endoleaks after endovascular aneurysm repair: A meta-analysis.
      • Sidloff D.A.
      • Stather P.W.
      • Choke E.
      • Bown M.J.
      • Sayers R.D.
      Type II endoleak after endovascular aneurysm repair.
      and I, II, and III for AKI.
      • Lee J.
      • Cho J.Y.
      • Lee H.J.
      • Jeong Y.Y.
      • Kim C.K.
      • Park B.K.
      • et al.
      Contrast-induced nephropathy in patients undergoing intravenous contrast-enhanced computed tomography in Korea: a multi-institutional study in 101487 patients.
      ,
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      Two lengths of excess hospital bed days as a result of AKI were included; Y and Z.
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      Definitions and assumptions of all parameter categories are summarised in Table 3. Estimates in this study did not consider direct costs of RRT, such as temporary haemodialysis.
      Table 3Definitions of endoleak incidence, acute kidney injury (AKI), renal replacement therapy (RRT) incidence, and number of excess bed days included in multivariable sensitivity analysis to estimate five year infrarenal endovascular aortic aneurysm repair (EVAR) surveillance costs for the Society of Vascular Surgery (SVS), European Society of Vascular Surgery (ESVS), National Institute of Health and Care Excellence (NICE), and local protocols
      Model parametersModel parameter valuesEvidence source
      Endoleak incidence
      Remaining patients in cohort assumed to have no endoleak.
      – %
      Type 1 or 3Type 2
       A00Extreme best case scenario
       B510Sidloff et al. (2013)
      • Sidloff D.A.
      • Stather P.W.
      • Choke E.
      • Bown M.J.
      • Sayers R.D.
      Type II endoleak after endovascular aneurysm repair.
      ; Quinn et al. (2017)
      • Quinn A.A.
      • Mehta M.
      • Teymouri M.J.
      • Keenan N.
      • Paty P.S.K.
      • Zhou Y.
      • et al.
      The incidence and fate of endoleaks vary between ruptured and elective endovascular abdominal aortic aneurysm repair.
       C1025Guo et al. (2017)
      • Guo Q.
      • Du X.
      • Zhao J.
      • Ma Y.
      • Huang B.
      • Yuan D.
      • et al.
      Prevalence and risk factors of type II endoleaks after endovascular aneurysm repair: A meta-analysis.
      ; Verzini et al. (2017)
      • Verzini F.
      • Romano L.
      • Parlani G.
      • Isernia G.
      • Simonte G.
      • Loschi D.
      • et al.
      Fourteen-year outcomes of abdominal aortic aneurysm endovascular repair with the Zenith stent graft.
      AKI incidence – %AKIRRT
       I00Extreme best case scenario
       II20.5Lee et al. (2014)
      • Lee J.
      • Cho J.Y.
      • Lee H.J.
      • Jeong Y.Y.
      • Kim C.K.
      • Park B.K.
      • et al.
      Contrast-induced nephropathy in patients undergoing intravenous contrast-enhanced computed tomography in Korea: a multi-institutional study in 101487 patients.
       III51Aubry et al. (2016)
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      Excess hospital bed daysAKIRRT
       Y1015N/A; conservative estimate
      Conservative estimate included for comparison with published estimate.
       Z1528Aubry et al. (2016)
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      N/A = not available; endoleak A = no endoleak; endoleak B = 5% type 1/3 endoleaks, 10% type 2 endoleaks, 85% no endoleak; endoleak C = 10% type 1/3 endoleak, 25% type 2 endoleak, 65% no endoleak; AKI I = no AKI; AKI II = 2% AKI, 0.5% RRT; AKI III = 5% AKI, 1% RRT; excess bed days Y = 10 days for AKI, 15 days for RRT; excess bed days Z = 15 days for AKI, 28 days for RRT.
      Remaining patients in cohort assumed to have no endoleak.
      Conservative estimate included for comparison with published estimate.
      Cost estimates were based on NHS tariff rates of £48 for CDUS, £85 for CTA, and £346 for an excess bed day.
      National Health Service (NHS)
      Reference costs 2016/2017.
      Mean annual attrition rate (inclusive of death, loss to follow up, relocation, or discharge from surveillance) was used to predict the remaining active surveillance patients each year post EVAR and was assumed to be linear for the five year period. The study complies with the Declaration of Helsinki and local ethics committee guidelines.

      Results

      Local endovascular aortic aneurysm repair surveillance analysis

      A total of 912 EVARs were referred for imaging surveillance between 2007 and 2019, of which 720 were infrarenal and therefore included in the analysis (87.2% male, median age 75.2 years, IQR 11 years, Fig. 2). Median surveillance duration was 57 months (IQR 53 months). The overall re-intervention rate was 20.7% (n = 149). Median time from initial procedure to re-intervention was 29.8 months (IQR 42 months). Early CTA assessments were performed on 653 (91.3%) patients, confirming adequate seal in 523 (72.6%) patients, adequate seal with a type 2 endoleak in 90 (12.5%) patients, and inadequate seal in 40 (5.6%) patients. Endoleaks occurring at any time during surveillance were detected in 239 patients (33.2%); 42 type 1 (5.8%), 184 type 2 (25.6%), 10 type 3 (1.4%) and three combined endoleaks (0.4%, two type 1 and 2, and one type 2 and 3). Median time to endoleak detection was 12.5 months (IQR 12 months). Of all endoleaks, 179 (74.9%) were detected in the first surveillance year and 60 (25.1%) subsequently. Forty (72.9%) type 1 and 3 endoleaks were detected in the first surveillance year and 15 (27.2%) subsequently. Twelve (1.7%) patients with an adequate seal on early CTA assessment developed a type 1 or 3 endoleak during the follow up period (median time to detection of 35.5 months, range 8 – 96), seven (1.0%) occurring between one and five years post implantation. One concomitant type 2 endoleak was detected in this group.
      Figure 2
      Figure 2Study flow chart for comparison of computed tomography angiography and colour duplex ultrasound surveillance post infrarenal endovascular aortic aneurysm repair (EVAR).
      Twelve patients (1.7%) in this cohort presented with post-implantation sac rupture (Table 4). Median time to sac rupture was 42.5 months. Three ruptures occurred as a result of late type 1 or 3 endoleak despite adequate seal on initial CTA assessment.
      Table 4Clinical details of patients presenting with post-infrarenal endovascular aortic aneurysm repair implantation ruptures amongst 720 patients
      PatientTime to rupture – moImaging findingsClinical presentationActionSurvival – days
      15Type 1a endoleak detected on CTA and CDUS 1 mo post EVARPresented with sudden abdominal pain; rupture occurred between diagnosis and elective treatmentProximal extension>30
      213Endoleak detected on 1 y CDUS (type not defined); type 1a endoleak detected on CTAOnset sudden abdominal pain; small, contained rupture detected on CTADevice relining>30
      316Type 2 and possible type 1 endoleaks detected 4 mo prior to rupturePrevious known type 2 endoleak, presented with sudden lower back pain; type 2 and 1 endoleaks confirmed peri-operatively; rupture occurred between CDUS detection of endoleak and symptom onsetProximal cuff>30
      424Type 2 endoleak with small sac increase detected 1 y previous to rupture, not detected on confirmatory CTAPresentation unknown; known previous type 2 endoleak with sac increase – type 1b additionally detected peri-operativelyLeft limb extension14
      540No endoleak detected on routine annual CDUS assessmentsSudden onset back pain 6 mo after previous CDUS assessment; endoleak confirmed peri-operatively (type not reported)Proximal cuff>30
      640Type 3 endoleak reported on CDUS, reported as type 2 on CTA; CTA confirmed type 3 6 mo laterSevere back pain 6 mo after type 3 endoleak confirmed with CTA; rupture occurred between diagnosis and elective treatmentProximal extension and left renal chimney graft5
      745Increase in sac size CDUS, type 1b confirmed on CTARupture occurred prior to multidisciplinary planningDistal left limb extension>30
      847Poor apposition of stent to aortic wall reported on CDUS, no confirmatory CTA occurredSudden collapse. Type 1a endoleak confirmed peri-operatively. Patient died as a result of bleeding during procedureProximal extension (patient died)0
      963Large type 3 endoleak detected with CDUS, confirmed with CTAAbdominal pain and palpable pulsatile mass. Previous type 3 endoleaks treated at 6 and 18 mo mitigating rupture; large type 3 and 1b endoleaks confirmed peri-operativelyRight limb extension and left limb relining (unsuccessful)13
      1068Persistent type 2 endoleak and sac expansion detected with CDUS, increase size of leak confirmed with CTA – conservative treatmentSudden abdominal pain and collapse. Known type 2 endoleak treated conservatively, type 1b endoleak confirmed on CTA peri-operativelyRight limb extension>30
      1172Type 1b detected with CDUS, confirmed with CTAConservative treatment as high risk. Abdominal and left leg pain; rupture 3 y after endoleak initially detectedLeft limb extension (conservative prior to rupture)3
      1283Type 2 endoleak detected with CDUS, sac size reduction – not followed up with CTAPresentation unknown; left limb stent dislocation detected peri-operativelyCoil occlusion of left limb with right-left crossover graft>30
      All patients underwent surveillance imaging in the 12 months prior to the sac rupture. CDUS = colour duplex ultrasound; CTA = computed tomography angiography.
      Long term follow up data were available for a total of 303 patients who remained on surveillance for a minimum of five years. The median follow up at time of analysis in this group was 88 months (IQR 34.5 months). In the long term follow up group, 13 initial re-interventions occurred for high risk endoleaks beyond five years.
      A total of 309 CDUS and CTA scans occurred within a four week window and were included in the agreement analysis. The coefficient between CDUS and CTA for detecting sac abnormalities was 0.68, indicating good agreement. Eight false negatives were recorded on CDUS when detecting type 1 and 3 endoleaks; four were classified as type 2 endoleaks with significant sac expansion and three were reported as significant sac expansion with no detectable endoleak. One small type 1a was detected by CTA; however, was not visualised on CDUS. This remained untreated and resolved without surgical intervention.

      Surveillance financial sensitivity analysis

      Total costs of five year SVS, ESVS, NICE, and local surveillance protocols were estimated from the 289 active surveillance patients as of May 2019. A mean five year post-operative attrition rate of 15% was estimated from the full cohort data. Application of the estimated attrition rate resulted in the patients included in analysis decreasing to 246, 209, 177, and 151 in years two, three, four, and five, respectively. Total imaging costs, excluding any endoleaks, were £81 593 for the SVS, £37 388 for the ESVS, £115 668 for the NICE protocols, and £76 011 for local protocol. SVS costs increased to £87 309 for endoleak category B and £95 003 for category C. ESVS increased to £44 265 and £53 352, respectively, NICE increased to £119 352 and £122 794, respectively, and the local protocol to £81 727 and £89 421, respectively. Increases in endoleak incidence resulted in a 1.1 fold increase in cost for both the SVS and NICE protocols, a 1.2 fold increase for local protocol, and a 1.4 fold increase for the ESVS protocols.
      Overall five year surveillance costs, and costs on a per patient basis, factoring varying incidences of endoleaks, AKI, the need for RRT, and number of excess bed days are shown in Table 5 and Fig. 3A–E. Surveillance cost estimates range from £81 953 to £272 359 for SVS, £37 388 to £230 708 for ESVS, £115 668 to £643 802 for NICE, and £76 011 to £266 777 for local protocols, a respective 3.3, 6.2, 5.6, and 3.5 fold increase in cost between the minimum and maximum estimates. The maximum estimated difference in cost reduction vs. NICE protocols, was £371 443 for SVS, £413 094 for ESVS, and £377 025 for local protocols equating to a 58%, 64%, and 59% reduction, respectively.
      Table 5Estimated overall and per patient costs of a five year post infrarenal endovascular aortic aneurysm repair (EVAR) surveillance programme comparing Society of Vascular Surgery (SVS), European Society of Vascular Surgery (ESVS), National Institute of Health and Care Excellence (NICE), and local protocols. A multivariable sensitivity analysis was conducted comparing variations in endoleak incidence, acute kidney injury (AKI) / renal replacement therapy (RRT) incidence, and number of excess bed days
      AKI/RRT incidence
      IIIIII
      ProtocolEndoleak incidenceExcess bed daysExcess bed daysExcess bed days
      YZYZYZ
      SVSA81 593 (381)81 593 (381)123 446 (576)148 557 (693)180 517 (842)238 350 (1 112)
      B87 309 (407)87 309 (407)131 259 (612)157 838 (736)192 733 (899)254 366 (1 186)
      C95 003 (443)95 003 (443)142 355 (664)170 766 (796)206 926 (965)272 359 (1 270)
      ESVSA37 388 (174)37 388 (174)79 241 (370)104 352 (487)136 313 (636)194 145 (906)
      B44 265 (206)44 265 (206)88 868 (414)115 629 (539)149 689 (698)211 322 (986)
      C53 352 (249)53 352 (249)100 705 (470)129 116 (602)165 276 (771)230 708 (1 076)
      NICEA115 668 (539)115 668 (539)245 147 (1 143)322 835 (1 506)421 710 (1 967)600 627 (2 801)
      B119 352 (557)119 352 (557)252 957 (1 180)333 119 (1 554)435 144 (2 030)619 761 (2 891)
      C122 794 (573)122 794 (573)262 536 (1 225)346 317 (1 615)451 586 (2 106)643 802 (3 003)
      LocalA76 011 (355)76 011 (355)117 864 (550)142 975 (667)174 936 (816)232 768 (1 086)
      B81 728 (381)81 728 (381)125 678 (586)152 256 (710)187 152 (873)248 784 (1 160)
      C89 421 (417)89 421 (417)136 773 (638)165 185 (770)201 344 (939)266 777 (1 244)
      Values are presented in £. Values in brackets represent the cost of surveillance per patient assuming full compliance for the five year surveillance period. Endoleak A = no endoleak; endoleak B = 5% type 1/3 endoleaks, 10% type 2 endoleaks, 85% no endoleak; endoleak C = 10% type 1/3 endoleak, 25% type 2 endoleak, 65% no endoleak; AKI I = no AKI; AKI II = 2% AKI, 0.5% RRT; AKI III = 5% AKI, 1% RRT; excess bed days Y = 10 days for AKI, 15 days for RRT; excess bed days Z = 15 days for AKI, 28 days for RRT.
      Figure 3
      Figure 3Graphical representation of estimated cumulative costs of a five year post-infrarenal endovascular aortic aneurysm repair (EVAR) surveillance programme comparing the Society of Vascular Surgery (SVS), European Society of Vascular Surgery (ESVS), National Institute of Health and Care Excellence (NICE), and local protocols. A multivariable sensitivity analysis was conducted comparing variations in endoleak incidence, acute kidney injury (AKI) incidence, and number of excess bed days. Each graph (A–E) illustrates differences in costs estimates based on changes in AKI incidence and number of excess bed days stated. Excess bed days (EBDs) are not applicable for (A) because of the assumption of no AKI or renal replacement therapy (RRT). Endoleak A = no endoleak; Endoleak B = 5% type 1/3 endoleaks, 10% type 2 endoleaks, 85% no endoleak; Endoleak C = 10% type 1/3 endoleak, 25% type 2 endoleak, 65% no endoleak.
      The estimated number of CTAs for the surveillance period for the NICE protocol was 1 361 in the absence of endoleak, 1 404 for endoleak category B, and 1 462 for endoleak category C. For both the SVS and ESVS protocols, this was 440, 469, and 498 CTAs, respectively. CTAs were reduced to 289, 318, and 347, respectively, in the local protocol. The estimated number of excess bed days for the surveillance period for the NICE protocol ranged from 374 to 950 days depending on endoleak and AKI incidence. For both the SVS and ESVS protocols, this was 121 to 233 days, and for the local protocol 80 to 225 days.

      Discussion

      EVAR imaging surveillance is a considerable, long term cost to health services. Variation in international surveillance protocols persists, with international guidelines from the SVS,
      • Chaikof E.L.
      • Dalman R.L.
      • Eskandari M.K.
      • Jackson B.M.
      • Lee W.A.
      • Ashraf M.
      • et al.
      The Society of Vascular Surgery practice guidelines on the care of patients with an abdominal aortic aneurysm.
      ESVS,
      • Wanhainen A.
      • Verzini F.
      • van Herzeele I.
      • Allaire E.
      • Bown M.
      • Cohnert T.
      • et al.
      European Society for Vascular Surgery (ESVS) 2019 Clinical practice guidelines on the management of abdominal aorto-iliac artery aneurysms.
      and NICE

      National Institute for Health and Care Excellence (NICE). Abdominal aortic aneurysm: diagnosis and management (NICE guideline [NG156]). Available from https://www.nice.org.uk/guidance/ng156. [Accessed 20 Mar 2020].

      proposing different combined CTA and CDUS surveillance protocols. By constructing a hypothetical model, this study has estimated and compared five year financial implications of the SVS, ESVS, NICE, and local EVAR surveillance guidelines. A multivariable sensitivity analysis was conducted to determine what impact variations in endoleaks, AKI incidence, and excess bed days have on surveillance costs. Inclusion of different proportions of patients at different risk of EVAR failure provides a more representative analysis of the differences between surveillance strategies and considers different use of resources and expenditure, depending on presence of abnormalities and subsequent surveillance intensity.
      Cost estimates calculated in this study show a modest increase in expenditure with increases in the incidence of endoleaks as a result of increased scan frequency, resulting in between a 1.1 and 1.4 fold increase depending on protocol. Frequent use of CTAs is associated with potential renal impairment, with reports of AKI and RRT ranging from 2% to 5%
      • Lee J.
      • Cho J.Y.
      • Lee H.J.
      • Jeong Y.Y.
      • Kim C.K.
      • Park B.K.
      • et al.
      Contrast-induced nephropathy in patients undergoing intravenous contrast-enhanced computed tomography in Korea: a multi-institutional study in 101487 patients.
      • Mitchell A.M.
      • Jones A.E.
      • Tumlin J.A.
      • Kline J.A.
      Incidence of contrast-induced nephropathy after contrast-enhanced computed tomography in the outpatient setting.
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      and 0.5% to 1%,
      • Aubry P.
      • Brillet G.
      • Catella L.
      • Schmidt A.
      • Bénard S.
      Outcomes, risk factors and health burden of contrast-induced acute kidney injury: an observational study of one million hospitalizations with image-guided cardiovascular procedures.
      ,
      • Moos S.I.
      • van Vemde D.N.H.
      • Stoker J.
      • Bipat S.
      Contrast induced nephropathy in patients undergoing intravenous (IV) contrast enhanced computed tomography (CECT) and the relationship with risk factors: a meta-analysis.
      respectively. A large European study observed a mean additional hospital stay of 15 days in patients with AKI and 28 in patients with RRT.
      • Mitchell A.M.
      • Jones A.E.
      • Tumlin J.A.
      • Kline J.A.
      Incidence of contrast-induced nephropathy after contrast-enhanced computed tomography in the outpatient setting.
      The inclusion of AKI and RRT demonstrated that differences in costs in this model are driven largely by increased length of hospital stay as a result of AKI, with the direct cost of imaging modality and endoleak incidence associated with a comparatively minor contribution. The NICE surveillance protocol was a minimum of £374 000 more expensive than the SVS, ESVS, and local protocol over five years when including excess bed days. Overall costs translate to a maximum cost per patient of £1 270, £1 076, £3 003, and £1 244 for the SVS, ESVS, NICE, and local protocols, respectively, assuming full compliance for the five years. Endoleak detection and re-intervention rates of 33% and 21%, respectively, indicate that additional scans, and further costs, outside of these estimates are likely. Furthermore, the typical EVAR populations are inherently older and afflicted with a range of comorbidities, further increasing their risk of AKI.
      • Moos S.I.
      • van Vemde D.N.H.
      • Stoker J.
      • Bipat S.
      Contrast induced nephropathy in patients undergoing intravenous (IV) contrast enhanced computed tomography (CECT) and the relationship with risk factors: a meta-analysis.
      Whilst several studies concluded that CDUS is not sufficiently accurate for EVAR surveillance,
      • AbuRahma A.F.
      • Welch C.A.
      • Mullins B.B.
      • Dyer B.
      Computed tomography versus color duplex ultrasound for surveillance of abdominal aortic stent-grafts.
      ,
      • Cantisani V.
      • Ricci P.
      • Grazhdani H.
      • Napoli A.
      • Fanelli F.
      • Catalano C.
      • et al.
      Prospective comparative analysis of colour-Doppler ultrasound, contrast-enhanced ultrasound, computed tomography and magnetic resonance in detecting endoleak after endovascular abdominal aortic aneurysm repair.
      others have demonstrated high accuracy and sensitivity in detecting abnormalities.
      • Baderkhan H.
      • Wanhainen H.
      • Haller O.
      • Björk M.
      • Mani K.
      Detection of late complications after endovascular abdominal aortic aneurysm repair and implications for follow up based on retrospective assessment of a two centre cohort.
      ,
      • Abraha I.
      • Luchetta M.L.
      • De Florio R.
      • Cozzolino F.
      • Casazza G.
      • Duca P.
      • et al.
      Ultrasonography for endoleak detection after endoluminal abdominal aortic aneurysm repair.
      • Beeman B.R.
      • Doctor L.M.
      • Doerr K.
      • McAfee-Bennett S.
      • Dougherty M.J.
      • Calligaro K.D.
      Duplex ultrasound imaging alone is sufficient for midterm endovascular aneurysm repair surveillance: a cost analysis study and prospective comparison with computed tomography scan.
      • Gray C.
      • Goodman P.
      • Herron C.C.
      • Lawler L.P.
      • O’Malley M.K.
      • O’Donohue M.K.
      • et al.
      Use of colour duplex ultrasound as a first line surveillance tool following EVAR is associated with a reduction in cost without compromising accuracy.
      • Cantador A.A.
      • Siqueira D.E.
      • Jacobsen O.B.
      • Baracat J.
      • Pereira I.M.
      • Menezes F.H.
      • et al.
      Duplex ultrasound and computed tomography angiography in the follow-up of endovascular abdominal aortic aneurysm repair: a comparative study.
      The nature of the local surveillance considered in the present study means that scans compared occurred predominantly as a result of suspected abnormalities on CDUS, thereby limiting the applicability of sensitivity and specificity to the overall infrarenal population. The observed coefficient of agreement of 0.68 supports the accuracy of CDUS for sac abnormality detection. Baderkhan et al.
      • Baderkhan H.
      • Wanhainen H.
      • Haller O.
      • Björk M.
      • Mani K.
      Detection of late complications after endovascular abdominal aortic aneurysm repair and implications for follow up based on retrospective assessment of a two centre cohort.
      recently reported higher agreement; however, this is likely to be explained by 35 false positives in the present analysis, 33 of which were benign type 2 endoleaks. Correct identification of clinically significant findings, such as high risk endoleaks and sac expansion, should be considered a more informative indicator of surveillance success than traditional classification. Misclassification of high risk endoleaks in eight patients was mitigated in seven cases when combined with sac expansion. Accuracy and reproducibility of CDUS sac size measurements have been reported frequently,
      • Beeman B.R.
      • Doctor L.M.
      • Doerr K.
      • McAfee-Bennett S.
      • Dougherty M.J.
      • Calligaro K.D.
      Duplex ultrasound imaging alone is sufficient for midterm endovascular aneurysm repair surveillance: a cost analysis study and prospective comparison with computed tomography scan.
      • Gray C.
      • Goodman P.
      • Herron C.C.
      • Lawler L.P.
      • O’Malley M.K.
      • O’Donohue M.K.
      • et al.
      Use of colour duplex ultrasound as a first line surveillance tool following EVAR is associated with a reduction in cost without compromising accuracy.
      • Cantador A.A.
      • Siqueira D.E.
      • Jacobsen O.B.
      • Baracat J.
      • Pereira I.M.
      • Menezes F.H.
      • et al.
      Duplex ultrasound and computed tomography angiography in the follow-up of endovascular abdominal aortic aneurysm repair: a comparative study.
      and identifying sac increases plays an important role in identifying abnormalities in the absence of clear evidence of an endoleak. Referral for confirmatory CTA in these instances emphasises the importance of using CDUS and CTA in a complementary manner. Ultimately, surveillance requires high sensitivity to identify patients who require attention, while doing minimal harm in observation of the remaining surveillance population. Reserving CTA for inconclusive CDUS scans, confirmatory imaging, and surgical planning prior to re-intervention reduces both the risk and cost of surveillance.
      • Cantador A.A.
      • Siqueira D.E.
      • Jacobsen O.B.
      • Baracat J.
      • Pereira I.M.
      • Menezes F.H.
      • et al.
      Duplex ultrasound and computed tomography angiography in the follow-up of endovascular abdominal aortic aneurysm repair: a comparative study.
      Device seal assessment by CDUS is limited, therefore an early CTA, as universally recommended by SVS, ESVS, and NICE guidelines, addresses this important limitation. Adequate seal in the early follow up period improves the likelihood of successful EVAR sac exclusion and identifies those at increased risk of developing complications.
      • Baderkhan H.
      • Wanhainen H.
      • Haller O.
      • Björk M.
      • Mani K.
      Detection of late complications after endovascular abdominal aortic aneurysm repair and implications for follow up based on retrospective assessment of a two centre cohort.
      The ESVS guidelines suggest postponement of surveillance to a further CTA at five years based on confirmation of adequate seal on early CTA. In the current cohort, there were seven patients who developed a high risk endoleak between one and five years post EVAR despite CTA confirmation of adequate seal; three of which ruptured. Rupture in the remaining four patients was mitigated by re-intervention on the basis of CDUS findings, followed by CTA confirmation. This small, but non-negligible, group particularly benefitted from annual CDUS surveillance scans. Annual CDUS as performed locally and recommended in the SVS guidelines is ∼£40 000 more expensive over this five year model; however, allows for periodic updates in sac status. Exclusion of the five year CTA unless clinically indicated reduces the number of CTAs in the present authors’ local protocol vs. the international guidelines. However, long term success of EVAR remains controversial and disease progression and material fatigue play a role in late treatment failures.
      • Wanhainen A.
      • Verzini F.
      • van Herzeele I.
      • Allaire E.
      • Bown M.
      • Cohnert T.
      • et al.
      European Society for Vascular Surgery (ESVS) 2019 Clinical practice guidelines on the management of abdominal aorto-iliac artery aneurysms.
      High risk endoleaks were observed in the present series beyond five years. Additional CTA surveillance to address this concern is recommended by the ESVS, particularly as CDUS is largely unable to detect changes in sealing zones, and detects only high pressure endoleaks once they are already compromising the sac. However, evidence for the optimal timing of additional CTA surveillance remains uncertain.
      In the present authors’ experience, CTA surveillance for infrarenal EVAR creates a large number of redundant scans and improvement in patient outcomes is not immediately apparent. The current study expands on earlier experience at the study centre,
      • Black S.A.
      • Carrell T.W.G.
      • Bell R.E.
      • Waltham M.
      • Reidy J.
      • Taylor P.R.
      Long-term surveillance with computed tomography after endovascular aneurysm repair may not be justified.
      with a greater number of patients and longer follow up duration. A larger number of abnormalities and re-interventions detected in these contemporary data reinforces the need for ongoing surveillance; however, both studies postulate that CTA surveillance is probably overused in the infrarenal EVAR population. A maximum of 498 CTA scans was associated with both the SVS and ESVS protocols, and 347 for the local protocol. Irrespective of endoleak incidence, the NICE strategy was associated with approximately 1 000 additional CTAs in this model. A greater number of CTAs results in increased cumulative radiation exposure, a risk eliminated by the use of CDUS. The extent to which cancer risk is elevated in older populations is outside the scope of this study; however, it is an important consideration.
      This study has shown that in a large centre, with appropriate expertise, a surveillance protocol incorporating an early CTA seal assessment, followed by annual CDUS and confirmatory CTA where necessary, is an effective surveillance protocol. Approximately 80% of patients included in this study did not require any intervention during surveillance, therefore CTAs would have provided no clinical benefit. A CTA based surveillance strategy requires significant health service resources when CDUS provides a cheaper alternative without the loss of crucial diagnostic information in the infrarenal EVAR population. Because of the complex anatomy, proximal stent graft placement, and the physical limitations of CDUS, the same conclusions cannot be applied to patients requiring complex EVAR.
      The primary limitation of this study is the retrospective design of data collection and potential for reporting errors. As a result of the development of the local surveillance protocol, dual CTA and CDUS scanning was not available for the majority of patients who underwent EVAR after 2007. Consequently, comparisons in most patients occurred where CDUS detected an abnormality and CTA confirmation was required. As CTAs were predominantly prompted by suspected CDUS abnormalities, analysis of sensitivity and specificity is suboptimal because of selection bias. On this basis it is not possible to exclude abnormalities missed by CDUS had the patient undergone simultaneous CTA in all instances. Similarly, because of the retrospective design of the study it was not possible to blind the operator to both the CTA and CDUS from the results of the other modality, further limiting direct modality comparisons. Costs were estimated by factoring in potential implications of CIN, although there remains controversy as to whether CIN associated AKI is overestimated.
      • Rudnick M.R.
      • Leonberg-Yoo A.K.
      • Cohen R.M.
      • Hilton S.
      • Reese P.P.
      The controversy of contrast-induced nephropathy with intravenous contrast: what is the risk?.
      Incidence of AKI post CTA has been shown to be comparable with the parameter values included in the financial model irrespective of the use of contrast media or patient renal function.
      • McDonald J.S.
      • McDonald R.J.
      • Carter R.E.
      • Katzberg R.W.
      • Kallmes D.F.
      • Williamson E.E.
      Risk of intravenous contrast material-mediated acute kidney injury: a prospective score-matched study stratified by baseline-estimated glomerular filtration rate.
      Incidence of AKI, and therefore financial costs, would increase if high risk patients were exposed to contrast media.
      • Rudnick M.R.
      • Leonberg-Yoo A.K.
      • Cohen R.M.
      • Hilton S.
      • Reese P.P.
      The controversy of contrast-induced nephropathy with intravenous contrast: what is the risk?.
      ,
      • McDonald J.S.
      • McDonald R.J.
      • Carter R.E.
      • Katzberg R.W.
      • Kallmes D.F.
      • Williamson E.E.
      Risk of intravenous contrast material-mediated acute kidney injury: a prospective score-matched study stratified by baseline-estimated glomerular filtration rate.
      Preventive measures such as pre-hydration therapy were not included in this study, but these would mitigate this complication to some degree. Finally, there are inherent issues with widespread CDUS surveillance because of unevenly distributed operator experience and expertise. Consequently, the potential difficulties of providing such a surveillance programme in regional spoke hospitals without sufficient training and exposure are acknowledged.

      Conclusion

      EVAR surveillance recommendations with increased use of CDUS or postponement of surveillance, reduce the number of CTAs and complications associated with repeat contrast exposure. AKI, as opposed to direct impact of imaging costs, accounted for the largest differences in cost estimates in this analysis. A combined CTA and CDUS surveillance protocol, with CTA reserved for early seal assessment and confirmatory imaging, provides an economical approach without comprising detection of sac abnormalities. A long term CTA assessment is recommended because of the limitations of CDUS in assessing device sealing zones; however, the optimal timing remains uncertain.

      Conflict of interest

      None.

      Funding

      None.

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      Linked Article

      • Maybe Neck Dilation Matters after All?
        European Journal of Vascular and Endovascular SurgeryVol. 62Issue 1
        • Preview
          Durability and long term success of endovascular aneurysm repair (EVAR) depends upon achieving and maintaining an appropriate proximal seal and fixation within the infrarenal aortic neck. Aortic neck dilation (AND) has been well documented in the existing literature and has been suggested as a potential source of critical EVAR failure through endoleaks and stent migration. Although other reports have suggested that AND occurs generally without clinical consequence, here, Oliveira et al. report that AND does in fact have an important relationship with EVAR failure in longer follow up in their large single centre experience.
        • Full-Text
        • PDF
        Open Archive
      • Post-Endovascular Aneurysm Repair Surveillance Needs Convergence on “Whom” and “How Often”
        European Journal of Vascular and Endovascular SurgeryVol. 62Issue 2
        • Preview
          The ideal modality and intensity of image surveillance after endovascular aneurysm repair (EVAR) remain undefined. This is well illustrated by the extraordinary variability in protocols adopted by institutions and important differences in recommendations made by scientific societies and regulatory bodies. The problem is magnified by evidence of large proportions of patients lost to follow up, a strong signal that whatever the adopted strategy, it is hard to maintain. Surveillance after EVAR is evidently an unresolved issue with too many uncertainties.
        • Full-Text
        • PDF
        Open Archive

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