Eur J Vasc Endovasc Surg (2011) 42, 585e590
Heterogeneity in Surveillance after Endovascular Aneurysm Repair in the UK A. Karthikesalingam, A.A. Page, C. Pettengell, R.J. Hinchliffe, I.M. Loftus, M.M. Thompson, P.J.E. Holt* Department of Outcomes Research, St George’s Vascular Institute, London SW17 0QT, UK Submitted 24 May 2011; accepted 29 June 2011 Available online 23 July 2011
KEYWORDS EVAR; Surveillance; Reintervention; Survey; Post-operative
Abstract Objectives: Surveillance after Endovascular Aneurysm Repair (EVAR) is considered mandatory, but the optimal regimen remains controversial. The aim of the present study was to report the nature of routine post-EVAR surveillance protocols in the UK, in order to identify the degree of variation in national practice and from the manufacturer’s instructions for use (IFU). Methods: A telephone survey was administered to 41 centres with 10 years’ experience in EVAR to identify their standard surveillance protocol after EVAR. Data were collected regarding the number of surveillance CT or ultrasound performed up to 5 years postoperatively. Results: 12/41 centres used CT as the primary mode of surveillance, 14/41 centres used USS as the primary mode of surveillance, and 15/41 centres used a combination of CT and USS. The mean s.d. number of CT scans performed cumulatively up to 1 year and 5 years post surgery were 1.1 0.6 and 3.5 2.9 respectively. The mean s.d. ultrasound scans performed at 1 year and 5 years post surgery were 0.5 0.9and 4.7 3.6 respectively. Conclusions: Significant heterogeneity exists in surveillance after EVAR in the UK. Efforts should be made to establish consensus towards a national surveillance protocol. Crown Copyright ª 2011 Published by Elsevier Ltd on behalf of European Society for Vascular Surgery. All rights reserved.
Introduction Endovascular repair (EVAR) of abdominal aortic aneurysms (AAA) has been shown to reduce peri-operative mortality
* Corresponding author. PJE Holt, St. George’s Vascular Institute, Room 4.007, St George’s Healthcare NHS Trust, Blackshaw Road, London SW17 0QT, UK. Tel.: þ44 (0)20 8725 3205; fax: þ44 (0)20 8725 3495. E-mail address:
[email protected] (P.J.E. Holt).
compared to open repair, but is associated with a higher rate of subsequent reintervention and aortic rupture.1,2 Long-term follow-up data from randomised controlled trials (RCTs) suggest that a significant rate of graft-related complications persists up to 8 years after EVAR.3,4 These findings are consistent with a pooled survival analysis of over 10,000 patients, which reported reintervention-free survival in 81.5% of cases after 5 years, with a linear requirement for reintervention.5 Lifelong post-operative surveillance is therefore considered mandatory to identify graft-related complications and to direct reintervention.
1078-5884/$36 Crown Copyright ª 2011 Published by Elsevier Ltd on behalf of European Society for Vascular Surgery. All rights reserved. doi:10.1016/j.ejvs.2011.06.053
586 Many centres initially adopted surveillance protocols from those outlined in RCTs or early registries, which used contrast-enhanced Computed Tomography (CT) as the gold standard of surveillance.1 However, excessive reliance on CT is expensive6 and necessitates the repeated exposure of asymptomatic patients to nephrotoxic intravenous contrast7 and ionising radiation.8 Increasing the proportional use of non-nephrotoxic imaging modalities after EVAR has been subsequently advocated as an alternative strategy to reduce surveillance-related morbidity.9 An increased reliance on duplex ultrasound appears a safe strategy in selected patients, and offers reasonable accuracy compared to CT for endoleak detection.10e12 The modality, timing and overall necessity of surveillance remain controversial11 and surveillance accounts for a significant proportion of the long-term excess cost of EVAR compared to open repair.13 In light of changing trends for post-EVAR surveillance and improvements in the design of endovascular stent-grafts, there is a need for a contemporary appraisal of surveillance after EVAR in the UK. The aim of the present study was to report the nature of routine post-EVAR surveillance protocols in current use throughout the UK, in order to identify the degree of variation in national practice and the degree of variation from the manufacturer’s instructions for use (IFU).
Methods To interrogate variation in national practice and to limit the potential confounding effect of technical inexperience, a list of centres with at least 10 years’ experience in EVAR in the UK was desired. The inclusion criteria of this study were therefore limited to 41 centres that had been enrolled in the EVAR-1 trial.1 Representatives from each centre were contacted and a standardised clinical scenario was administered by telephone and email. The survey was conducted during a 3month period starting in June 2010. Responses were obtained from both a consultant vascular surgeon and an associated healthcare professional (junior surgeon, sonographer or specialist nurse) at each centre, and a consensus opinion for each response was required and obtained for inclusion in the study. Differences in opinion were resolved through the representative consultant in each centre. In order to minimise variation in respondents’ approaches to patient preference, operative complexity and types of endograft, a standard clinical scenario was chosen and presented to survey respondents as follows: “Questions relate to a 65-year old healthy male infrarenal EVAR patient with no co-morbidities. He lives near to the hospital, is independent and has no objections to surveillance. The operation was successful with no complications. He had a Cook Zenith stent-graft placed within the manufacturer’s indications for use (IFU)(Cook Medical, Bloomington, Indiana, USA). Technical success and Clinical Success were achieved as per consensus definitions.14 What is your routine surveillance imaging protocol in this patient?” To minimise bias, data were collected and stored by two non-specialist junior doctors (AAP, CP) using a standardised web-hosted proforma constructed using Filemaker Pro
A. Karthikesalingam et al. software, version 10 (Filemaker Inc., Santa Clara, CA, USA). Respondents were specifically interrogated to obtain data regarding the number of CT, ultrasound (USS), plain abdominal radiography, or angiographic examinations performed at set post-operative timepoints: at discharge from hospital, 6 weeks, 3 months, 1 year, 3 years and 5 years postoperatively. Descriptive analysis of survey responses was performed using SPSS software, version 16.0 (SPSS Inc., Chicago Ill, USA). No funding was received for this study and no device manufacturers were involved in the study.
Results All 41 EVAR-1 centres participated and the response rate was complete at 100%. Concordant responses were obtained from 2 representatives at all 41 UK EVAR-1 centres. 12/41 centres used CT as the primary mode of surveillance, 14/41 centres used USS as the primary mode of surveillance, and 15/41 centres used a combination of CT and USS.
Imaging prior to discharge from hospital All 41 centres performed completion angiography at the end of EVAR. 18/41 (43.9%) performed 1-view angiography, 21/41 (51.2%) performed 2-view angiography and 2/41 (4.9%) performed rotational CT-angiography. 12/41 (29.3%) performed CT prior to discharge, 6/41 (14.6%) performed duplex USS prior to discharge and 5/41 (12.2%) performed 2-view plain abdominal radiography prior to discharge. 24/ 41 centres performed neither CT nor duplex USS prior to discharge and in these centres 1-view completion angiography was performed in 11/24 (27%), 2-view completion angiography in 11/24 (27%) and rotational CT angiography in 2/24 (8.3%).
Computed tomography for EVAR surveillance The mean s.d. number of CT scans performed at the point of discharge and then cumulatively up to 6 weeks, 3 months, 1 year, 3 years and 5 years post surgery were 0 0.5, 0.9 0.5, 1.1 0.6, 2.1 1.2, 2.5 1.7, 2.8 2.0 and 3.5 2.9 (Fig. 1).
Duplex ultrasound for EVAR surveillance The mean s.d. Duplex Ultrasound scans performed at the point of discharge and then cumulatively up to 6 weeks, 3 months, 1 year, 3 years and 5 years post surgery were 0 0.3, 0.4 0.7, 0.5 0.9, 1.5 1.7, 2.3 2.1, 3.1 2.6 and 4.7 3.6 (Fig. 2). Duplex was performed in all centres by specialist vascular sonographers.
Plain abdominal radiography for EVAR surveillance The mean s.d. plain abdominal radiographs performed at the point of discharge and then cumulatively up to 6 weeks, 3 months, 1 year, 3 years and 5 years were 0 0.3, 0.3 0.5, 0.3 0.5, 1.1 1.2, 1.8 1.7, 2.4 2.3 and 3.5 3.3 (Fig. 3). Plain abdominal radiography was
Heterogeneity in Surveillance after Endovascular Aneurysm Repair in the UK
587
Figure 1 Cumulative use of Computed Tomography in EVAR Surveillance protocols currently employed by 41 UK EVAR-1 centres, and compared to the surveillance protocol specified in the manufacturer’s Instructions For Use (IFU).
performed as part of standard surveillance to ensure device integrity and assess for evidence of migration.
Removing patients from a postoperative surveillance program 11/41 (27%) of centres would remove the patient from surveillance after 5 years provided there was no evidence of endoleak, stent-graft migration or other complication requiring reintervention. 30/41 (73%) of centres would continue surveillance indefinitely.
Compliance with manufacturer’s IFU 3/41 centres were fully compliant with the manufacturer’s IFU for surveillance, which specified a CT scan should be performed at discharge or within 1 month postoperatively and subsequently at 3 months, 6 months and 12 months postoperatively, and annually thereafter (Fig. 1).15 10/41 centres were non-compliant because they did not conduct a CT scan within 1 month of the procedure (or at the time of discharge). 25/41 centres conducted a CT within 1 month but did not conduct a CT scan at 3 months post-procedure. 3/41 conducted CT scans within 1 month and at 3 months but did not conduct a CT scan at 6 months postoperatively.
Discussion The results of this survey demonstrated significant heterogeneity in the intensity and modality of post-operative
Figure 2
surveillance protocols employed across the UK at centres experienced in EVAR. The same patient undergoing infrarenal EVAR in the UK, within the manufacturer’s IFU and without the need for unexpected adjuncts, might receive no CT scans in 5 years following the operation, or undergo up to 10 CT scans in the same period, depending on which hospital performed the operation. This discrepancy was mirrored in the variation with which plain abdominal radiography and duplex ultrasound were used nationally. Whilst 27% of centres advocated cessation of surveillance in uncomplicated patients after 5 years, 73% of centres reported continuation of surveillance beyond this period and do not have a defined endpoint for surveillance. 3/41 (7.3%) of centres were compliant with the manufacturer’s IFU, which specified intensive CT surveillance. The heterogeneity seen in national practice reflects ongoing uncertainty surrounding the nature of surveillance that should be employed following EVAR. The long-term persistence of graft-related complications requiring reintervention justifies a continuing need for surveillance,5 yet the most effective method for surveillance remains unknown. In studies that have investigated the reasons underlying post-EVAR reintervention, it has been reported that 61e98% of re-interventions were initiated by the unexpected symptomatic presentation of patients independently of post-operative surveillance.16e18 These data suggest that surveillance protocols provided no benefit in at least 90% of patients as complications occur between surveillance scans.16e18 It has also been reported that 15% of post-EVAR aneurysm ruptures occur in patients with no stent abnormality detected on post-operative imaging.19
Cumulative use of Duplex Ultrasound in EVAR Surveillance protocols currently employed by 41 UK EVAR-1 centres.
588
Figure 3 centres.
A. Karthikesalingam et al.
Cumulative use of plain abdominal radiographs in EVAR Surveillance protocols currently employed by 41 UK EVAR-1
A limitation of the present study was the lack of information about variation in the clinical follow-up of patients after EVAR, which is of importance alongside radiological follow-up within the overall scheme of graft surveillance. Generic graft surveillance regimens that are the existing standard-of-care were derived from early multi-centre trials that employed earlier generations of endograft technology and were more heavily reliant on regular CT.1 The application of these data to present practice may lack validity in the face of changing trends in post-operative surveillance. Furthermore, intensive use of CT as seen in some centres (Fig. 1) may lead to cumulative renal injury sustained due to the repeated administration of nephrotoxic contrast agents.7,20,21 Cumulative Radiation exposure is also of concern. An estimated dose of 13 mSv per scan has previously been reported for CT in pre-operative EVAR planning.8 Based on this estimate, a patient’s radiation exposure in the present study varies from 13 mSv to 130 mSv during the first 5 years after EVAR in the UK. However, estimating the risk of malignancy due to cumulative abdominal CT is complex. The estimated lifetime attributable risk of cancer following a single 10-msV abdominal CT scan in a patient over 50 years old is small, approximately 0.02%.22 Cumulative CT has a stochastic effect on the risk of malignancy and although the probability of malignancy increases with each CT scan, its severity is independent of the total radiation dose sustained. Further variation is introduced by the effect of patient age, gender and the CT protocol employed.” It has been proposed that after one year CT can be reserved for those patients in whom ultrasound identifies growth or persistently unstable aneurysm diameter.23 Other studies have suggested that in the presence of normal imaging at one to three months, imaging at 6 months does not identify any clinically significant findings warranting intervention.24 Equally the efficacy of an early postprocedural CT, performed in 12/41 centres in the present study, has been questioned. It has been shown that this scan fails to influence treatment in 99% of cases,25 yet surveillance at this stage remains recommended in the manufacturer’s IFU15 and long-term data from the EVAR trials suggest it may prevent rupture by improving the detection and treatment of remediable complications.26 The medico-legal consequences of national variation in post-EVAR surveillance are of interest. Tests of medical
negligence in English law often include consideration of whether a doctor is in breach of “the practice of a responsible body of medical opinion”. Reference to the practice of a body of medical opinion in this manner is often termed the “Bolam test”.27 The present study highlights significant variation in practice amongst the specialist body of vascular surgeons in the UK. It could therefore be suggested that deviation from the Manufacturer’s surveillance guidelines might have few medico-legal consequences according to the “Bolam test”. However, the Bolam precedent has been challenged in more recent cases. Most significantly the judgement of the Bolitho case28 stated explicitly that “the court has to be satisfied that the exponents of the body of opinion relied upon can demonstrate that such opinion has a logical basis. In particular, in cases involving, as they so often do, the weighing of risks against benefits, the judge before accepting a body of opinion as being responsible, reasonable or respectable, will need to be satisfied that, in forming their views, the experts have directed their minds to the question of comparative risks and benefits”. This change in the legal status of clinical negligence claims further heightens the need for research to define optimal surveillance after EVAR. It has been hypothesised that the risk of reintervention after EVAR is not homogeneous,16 and it is of interest to consider proposals for surveillance in light of this. Increasing the proportional use of duplex USS after EVAR has been advocated to reduce surveillance-related morbidity9 and this may be a safe strategy in low-risk patients, whilst offering reasonable accuracy compared to CT for endoleak detection.10e12 Plain abdominal radiographs may depict stent-graft migration and component separation, offering a useful adjunct to duplex ultrasound surveillance. Oblique imaging can improve detection of wire fractures. Radiographs are, however, notoriously difficult to interpret with respect to lesser degrees of migration.29 The challenge of exact reproducibility, so as to avoid parallax assessment, limits reliance upon plain radiographs. The incidence of late endograft rupture demonstrated in the long-term results of the EVAR-1 trial highlight the need for more effective surveillance of high-risk patients.4 A formal analysis of data from EVAR-1 and EVAR-2 demonstrated that the presence of a complication requiring reintervention (type I or III endoleak, type II endoleak with
Heterogeneity in Surveillance after Endovascular Aneurysm Repair in the UK sac expansion, graft migration or kinking) was a significant predictor of post-EVAR rupture and the authors have highlighted the need for a low threshold towards reintervention to obtain a definitive solution for these patients (Hazard ratio 8.83).26 These long-term EVAR trial data support the hypothesis that the risk of reintervention after EVAR is not homogeneous and that there remains a high-risk subgroup, for which more intensive surveillance may be required than is provided by generic surveillance. In order to define these subgroups, study of the underlying determinants of reintervention after EVAR is required. Post-EVAR sac enlargement has been shown to correlate with hostile AAA neck diameter and angulation in addition to hostile common iliac artery diameter where these aspects of morphology were not compliant with the manufacturer’s IFU.30 It has been hypothesised that adverse aneurysm morphology may increase the risk of reintervention after EVAR, and further study of the relationship between reintervention and aneurysm morphology is required.16 This might allow consensus in risk-stratified surveillance, in which the intensity of rationalised surveillance could be stratified in proportion to reintervention risk to obtain the greatest clinical and economic efficacy. The incidence of peri-operative rupture following the omission of predischarge imaging in long-term data from the EVAR-1 and EVAR-2 trials has highlighted the need for quality control at the point of discharge. It is therefore of concern that 10/41 centres in the present study relied on 1-view angiography in the absence of CT or duplex imaging to ensure the absence of complications requiring reintervention.26 Current differences in surveillance intensity and modality could in theory lead to national differences in cost effectiveness, patient satisfaction, the development of renal dysfunction and overall outcomes after EVAR. The NIHR Health Technology Assessment of EVAR reported that surveillance accounted for 65% of the excess cost of EVAR compared to open repair, and that investigating optimal surveillance after EVAR should be a research priority.31 The results of the present study confirmed that surveillance after EVAR remains controversial, and represents an area of significant variation in national practice. Further research is urgently required to define a rationalised, clinically effective and cost-effective protocol for EVAR surveillance, which should be subject to a clinical trial following proof of its safety and efficacy.
Conclusion The results of this survey demonstrated significant heterogeneity in national practice for surveillance after EVAR, in terms of the intensity and duration of surveillance as well as the type of imaging modalities that were employed. The relationship between surveillance and reintervention after EVAR remains poorly understood. Efforts should be made to establish consensus towards a national surveillance protocol that is clinically and economically effective.
Conflicts of Interest None.
589
Funding None.
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