Costs of endovascular and open repair of thoracic aortic aneurysms

Abstract Background Repair of thoracic aortic aneurysms with either endovascular repair (TEVAR) or open surgical repair (OSR) represents major surgery, is costly and associated with significant complications. The aim of this study was to establish accurate costs of delivering TEVAR and OSR in a cohort of UK NHS patients suitable for open and endovascular treatment for the whole treatment pathway from admission and to discharge and 12-month follow-up. Methods A prospective study of UK NHS patients from 30 NHS vascular/cardiothoracic units in England aged ≥18, with distal arch/descending thoracic aortic aneurysms (CTAA) was undertaken. A multicentre prospective cost analysis of patients (recruited March 2014–July 2018, follow-up until July 2019) undergoing TEVAR or OSR was performed. Patients deemed suitable for open or endovascular repair were included in this study. A micro-costing approach was adopted. Results Some 115 patients having undergone TEVAR and 35 patients with OSR were identified. The mean (s.d.) cost of a TEVAR procedure was higher £26 536 (£9877) versus OSR £17 239 (£8043). Postoperative costs until discharge were lower for TEVAR £7484 (£7848) versus OSR £28 636 (£23 083). Therefore, total NHS costs from admission to discharge were lower for TEVAR £34 020 (£14 301), versus OSR £45 875 (£43 023). However, mean NHS costs for 12 months following the procedure were slightly higher for the TEVAR £5206 (£11 585) versus OSR £5039 (£11 994). Conclusions Surgical procedure costs were higher for TEVAR due to device costs. Total in-hospital costs were higher for OSR due to longer hospital and critical care stay. Follow-up costs over 12 months were slightly higher for TEVAR due to hospital readmissions.


Introduction
Patients with chronic thoracic aortic aneurysm disease (CTAA) are most often elderly with significant and multiple co-morbidity 1,2 .Nevertheless, patients are offered major surgical repair procedures such as endovascular stent grafting (TEVAR), potentially involving expensive technology, or open surgical repair (OSR), with costly intensive care stays and rehabilitation.Despite being effective for some CTAA patients, TEVAR and OSR are associated with significant complications [3][4][5] .Currently, there are no UK-specific economic studies assessing outcomes beyond the chosen procedure.
There was significant controversy regarding NICE recommendations for infrarenal aneurysm repair techniques in 2019 6 .Draft recommendations, driven largely by a lack of cost effectiveness and since revised, stated that TEVAR should not be used in the elective setting.The effect of similar interventions is therefore in the spotlight.Furthermore, centralization of specialist services has been a major policy focus in the UK in recent years, with evidence that outcomes for vascular surgery can be improved through centralization 7 .Services have undergone a substantial reorganization with amalgamation of smaller units and single-handed surgeons to form larger units.However, the structured organization of complex aneurysm surgery is still in its infancy.The costs of TEVAR and OSR procedures must be accurately determined to understand the tariffs that are required to allow services to be set up and managed and to identify where resources need to be pooled into specialist complex aortic hubs.With these issues in mind, and given the increasing demand for treatment due to an ageing population with rising prevalence of CTAA 2 , and limited NHS resources, further evidence regarding accurate costs of TEVAR and OSR procedures is needed.
Cost data is an important factor in developing clinical guidelines 8,9 , yet there is a sparsity of large multicentre micro-costing studies in Europe regarding TEVAR and OSR procedures that captures the whole treatment pathway from the procedure to discharge and subsequent follow-up.The Effective Treatment of Thoracic Aortic Aneurysms (ETTAA) study provided a unique opportunity to undertake a prospective micro-costing of a large cohort of patients with CTAA repaired https://doi.org/10.1093/bjs/znad378 Original Article with open and endovascular techniques.This study aims to establish accurate costs of delivering endovascular stent TEVAR and OSR in a cohort of UK NHS patients suitable for open and endovascular treatment for whole treatment pathway from admission and to discharge and 12-month follow-up.

Methods
The ETTAA study ETTAA was a large prospective observational cohort study of routine practice which recruited patients across 30 NHS vascular/cardiothoracic units in England.The protocol and funder's report are both published 10,11 with further details of the inclusion criteria but, briefly, consisted of patients ≥18 years of age who attended NHS hospitals in England between March 2014 and July 2018.Patients were included if they had a previously or newly diagnosed aneurysm with a diameter ≥4 cm in the arch or descending thoracic aorta.Exclusion criteria were acute dissection and previous surgical intervention for an aneurysm in the same segment of the aorta.Recruited patients were divided into four groups: watchful waits; conservative management; TEVAR; or OSR.

The micro-costing study
Important differences between the populations undergoing TEVAR and OSR in the ETTAA study raised concerns that any comparisons are biased because of unobserved or inadequately controlled confounding 11 .Therefore, this micro-costing study was based on a subset of the larger ETTAA patient population who, based on recorded study data, had no contraindication to either OSR or TEVAR, ensuring a fair comparison in terms of patient resource use and associated costs.Eligibility to receive either procedure was assessed by clinical experts.Reasons for OSR patients being ineligible for TEVAR included: aneurysm repair extending into the ascending aorta; concomitant cardiac procedures; and unsuitable aortic morphology.Reasons for TEVAR patients being ineligible for OSR included: BMI below 20 or above 35; NYHA IV dyspnoea; or age over 85.Additionally, 10 TEVAR patients had index procedures prior to enrolment in the study; these patients were excluded to maintain equipoise.
A multicentre prospective cost analysis of ETTAA patients undergoing surgical intervention with either OSR or TEVAR for patients with CTAA was performed and reported in accordance to the Consolidated Health Economic Evaluation reporting Standards (CHEERS) statement 12 and STROBE guidelines 13 .The micro-costing approach was adopted from the perspective of the UK NHS in order to improve the precision and accuracy of the cost estimate 14,15 and to undertake the 'direct enumeration and the costing of every resource input consumed in the treatment of a particular patient' 16,17 .The process involves the identification of all resources required for the provision of care; accurate measurement of each resource; and valuation of the resources used.The cost analysis focused on three stages based on chronological sequence of events: index (first) surgical procedure, post-procedure until discharge, and 12-months follow-up.For each patient, and for each stage of the cost analysis, all components of costs stratified by category of resource use were computed by multiplying units of resource use by their unit costs and summed.
Although capital equipment costs are incurred at a single point, it is typical to derive a cost for economic evaluation, whereby the initial cost of a capital asset is converted to annual equivalent sums over their expected lifetime.These annual costs are then discounted to reflect alternative investment or consumption opportunities forgone.In this study, capital equipment was discounted by 3.5 % per year 18 and the sum of these amounts was divided by their expected annual usage to obtain a cost per procedure 19 .

Identification and measurement of resource use
Resource utilization was identified and measured using information derived from expert clinical opinion and data collected in case report forms (CRFs), which were designed with expert guidance from members of the ETTAA collaboration including clinicians, statisticians and health economists.Details of resource use are presented in Tables S1, S2, S3 20 .Resources necessary to undertake the surgical procedures included staff, medical devices, reusable surgical equipment, consumables and overheads.A procedure CRF captured patient-level data on theatre time, type of graft, blood products used and perioperative complications, with other information such as surgical equipment provided by clinical experts based on a 'typical' procedure.
Resources necessary to provide postoperative care until discharge were collected using two CRFs.A post-procedure and discharge CRF captured the number of days in hospital, days in an intensive care unit or a high-dependency unit, postoperative blood product use, the use of any diagnostic investigations and any adverse events (including cardiac and renal failure).If a patient suffered an adverse event requiring a return to theatre, theatre time and reason for return to theatre were captured in a return-to-theatre CRF.These events were micro-costed using the same methods as described previously.
Use of NHS resources during a 12-month post-procedure follow-up including readmissions related to the aneurysm was collected at patient level using a study-specific follow-up CRF at 3, 6 and 12 months post-surgery.This included use of primary and community care and secondary care.If a patient was readmitted to hospital for reasons related to aneurysms, a hospital admission CRF captured length of stay by level of care.If a patient underwent another procedure during follow-up, this was captured using the same CRFs as the index procedure and was recorded as an additional procedure.Following discussion with experts, it was assumed that each patient who underwent TEVAR had a CT scan and a vascular outpatient visit at 1-month post discharge and annually thereafter, with OSR patients assumed to have a CT scan and a cardiology outpatient appointment at 6 months post-discharge and annually thereafter.

Unit costs
Unit costs were obtained in pounds Sterling from a variety of sources including national databases 21 , published studies 22 , stent graft device manufacturers and were inflated to 2018-19 prices using the healthcare and community health services inflation index 22 .Details of unit costs are reported in Tables S4, S5, S6 20 .

Statistical analysis
Baseline characteristics were summarized with cohorts compared using Student's t-test and Pearson's χ 2 test as appropriate.Costs for three stages (index procedure, post-procedure until discharge and follow-up) of the cost analysis were summed over all resource categories to obtain a total annual cost for each patient at 12 months.Costs were summarized and presented as mean (s.d.).Analysis was conducted using Stata v15.1.

Results
A total of 886 patients were recruited to the ETTAA study (Fig. S1).Of these, 601 patients did not have any surgical procedure consisting of watchful waits (n = 489) and conservative management (n = 112).The remaining patients had at least one type of surgical procedure, TEVAR (n = 150) and OSR (n = 135), as reported elsewhere 11 .Overall, 115 TEVAR and 35 OSR patients were judged potentially eligible for both procedures (no contraindications) and were included for primary comparison.These patients were recruited from 30 ETTAA sites, with participant numbers from each site presented in Table S8.Of the TEVAR patients, two required aortic arch endovascular repair, 97 required descending thoracic aortic repair and 16 required complex repair with thoracoabdominal stent with fenestrated or branch grafting.Of the 35 OSR patients, 13 required hybrid grafts (for example, using frozen elephant trunk grafts), 20 patients required standard thoracic repair, and two patients required thoracoabdominal aneurysm repair.A subgroup analysis was also performed highlighting the cost differences between procedures of differing complexity.

Patient characteristics
The patient characteristics of those deemed suitable for open and endovascular repair at baseline are presented in Table 1.

Subgroup analysis
Subgroup analysis was conducted to compare costs of procedures that differed in terms of complexity within TEVAR and OSR (Table 3).Within the TEVAR cohort, those undergoing aortic arch repair or complex repair thoracoabdominal stent with fenestrated or branch grafting had higher costs from admission until discharge £70 231 (£27 406) and £49 768 (£9 120) compared to TEVAR descending thoracic aortic repair £30 675 (£11 920).Both complex procedure types had higher cost estimated across all resource components compared to TEVAR descending thoracic aortic repair with aortic arch repair also being much higher than complex repair thoracoabdominal stent with fenestrated or branch grafting.The largest cost difference for the index procedure was due to the stent graft device cost (aortic arch £31 845 (£4320), complex repair thoracoabdominal stent with fenestrated or branch grafting £29 915 (£4753), descending thoracic aortic repair £19 266 (£8587)).The largest cost differences in the post-procedure until discharge period was due to length of stay, particularly critical care (aortic arch £16 171 (£18 860), complex repair thoracoabdominal stent with fenestrated or branch grafting £6695 (£4809), descending thoracic aortic repair £2929 (£4348)).
Within the OSR group, those with hybrid surgical grafts (n = 13) had a mean (s.d.) procedure cost almost twice as much as those with standard thoracic repair, £24 854 (£8258) and £12 757 (£5678), respectively.The two patients with thoracoabdominal repair had slightly higher procedure costs of £15 394 (£6598) versus standard thoracic repair.Higher procedure costs for hybrid graft patients were driven by the high expense of the surgical graft £13 545 (£3766).Costs until discharge were much lower for the hybrid group £17 199 (£11 259) compared to standard repair £26 191 (£27 351).However, thoracoabdominal repair had very high costs until discharge recorded, £127 421 (£152 054), driven by high critical care and length of stay costs.Overall, hybrid costs were the lowest of the OSR subgroups £42 023 (£14 218), followed by standard thoracic repair £48 151 (£53 541),  Due to small numbers, it is only appropriate to compare between descending thoracic aortic repair (TEVAR n = 97) and standard thoracic repair (OSR n = 20).Overall costs are higher in the standard thoracic repair OSR subgroup, with costs driven by critical care and ward days that occur in the post-procedure period.For descending thoracic aortic repair costs were driven by the high stent device costs that occur during the procedure.

Subgroup analysis
Subgroup analysis was conducted to compare costs of follow-up that differed in terms of complexity within TEVAR and OSR (Table 5).Within the TEVAR cohort, those undergoing complex repair thoracoabdominal stent with fenestrated or branch grafting had higher costs from follow-up £5912 (£11 152) compared to TEVAR descending thoracic aortic repair £4 794 (£11 180), with aortic arch endovascular repair having a much lower follow-up cost £684 (£274).Primary care and secondary care costs were similar between the different TEVAR groups.No hospital admissions or re-interventions were recorded for the aortic arch patients.There were five hospital readmissions recorded for those undergoing complex thoracoabdominal TEVAR with a mean (s.d.) cost of £11 112 (£2038) per readmission and 13 hospital readmissions recorded for descending thoracic repair with a mean (s.d.) cost of £4466 (£4267) per admission.Overall, aneurysm-related hospital admissions costs were higher for the complex TEVAR group £5051 (£11 077) versus descending thoracic repair £915 (£2881).Only the descending thoracic repair group had re-interventions recorded with a mean (s.d.) cost of £39 467 (£8527) per reintervention, resulting in a mean (s.d.) cost of £3087 (£10 882) across the cohort.
Within the OSR group, those with hybrid grafts (n = 8) had a much higher 12-month follow-up cost of £12 445 (£19 406) compared to £1455 (£1002) of those who underwent standard thoracic repair (n = 14).This higher cost was driven by re-interventions with the hybrid graft cohort recording four re-interventions with a mean (s.d.) cost of £22 468 (£31 639) per re-intervention, resulting in an mean (s.d.) cost of £11 234 (£19 442) across the hybrid graft group.There were no re-interventions recorded in the standard thoracic repair group.One aneurysm-related hospital admission was recorded in the standard thoracic repair group with a cost of £364, resulting in a  mean (s.d.) cost to the group of £23 (£91).Twelve-month follow-up costs were low, £507 (£239) for the thoracoabdominal aneurysm repair (n = 2) subgroup, with only secondary care recorded.Due to small numbers, it is only appropriate to compare subgroups between descending thoracic aortic repair (TEVAR n = 78) and standard thoracic repair (OSR n = 14).For these subgroups, TEVAR descending thoracic repair had a much higher mean 12-month cost compared to standard thoracic repair.Higher mean costs for descending thoracic repair were caused by higher recorded hospital admissions and reinterventions in this subgroup compared to standard thoracic repair.

Discussion
Although costing is undertaken from a UK NHS perspective, the micro-costing methodology provides a detailed insight into the true resource inputs of providing OSR and TEVAR in routine clinical care.The micro-costing methodology defined as the 'direct enumeration and costing of every input consumed in the treatment of a particular patient' 17 involves a number of stages, the first being a detailed insight into the identification of all the resources involved in the provision of care.This study has relevance in international settings as the micro-costing approach used may help inform future accurate renumeration studies as resource inputs are unlikely to differ across different healthcare systems, particularly in terms of the surgical procedure itself.This is important because accurate information regarding the costs of surgical interventions is vital to inform policy and guidance 23 , suggesting these findings are transferable where national prices can be applied.
Estimated mean costs from index procedure up until 12-month follow-up are higher for OSR relative to TEVAR, which is largely driven by differences in costs up until discharge.The procedure cost for TEVAR accounts for over three-quarters of mean total cost until discharge, with these driven by the costs of the endovascular stent graft device used.While the costs of OSR procedures are lower, there are higher costs until discharge, driven by length of stay in critical care.Mean follow-up costs up at 12 months were higher for TEVAR, driven by re-interventions, although these were not enough to outweigh the higher in-hospital costs of OSR.
The NHS England tariff (reimbursement) for TEVAR and OSR procedures does not include the cost of critical care, which is determined on a trust-by-trust basis, or the cost of the endovascular stent graft, which is funded centrally 21 .For a meaningful comparison with NHS tariff, critical care and stent costs were removed from the ETTAA patient cost estimates.The NHS England tariff for TEVAR in 2018-19, the same price year that our cost analysis was conducted, was £7880 for an elective complex procedure and £7272 for an elective simple procedure.TEVAR patients in the ETTAA study had a mean (s.d.) cost of £9370 (£5584), which was higher than the tariff.Furthermore, estimated mean (s.d.) costs for patients undergoing OSR was £24 023 (£25 621), which was also significantly higher than the £15 722 tariff.These costing estimates therefore have significant implications for hospitals, suggesting provision of treatment may not be adequately compensated.Centralization of services means this burden will be on larger specialist units.There are non-financial benefits of providing these treatments and a societal need to provide a regional service, but these results suggest there will be little incentive to continue this work from a financial point of view and calls for reorganization of payments may be welcomed.At the time of the ETTAA study, stent costs were negotiated on a hospital-by-hospital basis with manufacturers, with stent costs included in this study collected directly from manufacturers.However, the NHS moving towards central purchasing 24 of endovascular stent grafts may provide the opportunity to greatly reduce TEVAR procedure costs and make substantial cost savings.The development and introduction of more expensive and complex technology such as more sophisticated arch stent grafts should be carefully considered by health systems, particularly with high costs involved in these groups.
Previous studies conducted in the USA 25,26 estimated costs of TEVAR and OSR for open elective repair of descending thoracic aortas in a single centre using the hospital's accounting system found similar results regarding in-hospital cost drivers for each procedure.Endograft costs were a predictor of TEVAR costs with postoperative complications and length of stay being a predictor of OSR hospitalization costs.There is one other UK-based economic analysis that estimated costs of OSR and TEVAR from a consecutive series of 84 patients undergoing intervention on the descending aorta over a 13-year period using pre-, peri-and postoperative data from a single centre 27 .However, the procedure resources and associated costs were not micro-costed but based on a consensus regarding resource inputs with costs estimated at a 'broad level'.Hospital costs were estimated from NHS reference costs and included staff time, consumables and length of stay.The findings of this study are like ours where OSR Gray et al. | 5 incurred higher costs relating to staff, consumables, transfusion and length of stay.However, they report that stent costs of TEVAR completely outweighed these higher costs with no difference in total costs reported overall (median (i.q.r.) OSR £15 045 (£9299-£27 571) and TEVAR £16 694 (£13 352-£21 729), P = 0.41).These median costs are also much lower than those identified in our study, even accounting for inflation, possibly due to a less-precise costing approach undertaken.Most cost analyses of TAA repairs have only analysed hospital costs during the index hospitalization.Some of these studies have shown TEVAR to be less expensive due to shorter hospital stays with lower complication rates 25,28,29 , while others have shown no difference between open and endovascular repairs 27 .Other studies have reported overall lower hospitalization costs for TEVAR relative to OSR 30 .One study has evaluated costs beyond the initial hospital stay.Karimi et al. 25 evaluated their TAA cost data in a 57-patient, single-centre cohort for 2 years postintervention.They found that in-hospital and at 2 years postintervention, TEVAR was the more cost-effective option.Gillen et al. 30 conducted an in-hospital costing of both procedures and also assessed costs at 3 years utilizing a Monte Carlo simulation model and found that costs were also lower.However, except for Glade et al. 28 , who used data from three vascular centres in Amsterdam, most of these studies estimated in-hospital costs from a single-centre institution.These details of resource utilization and associated costs were estimated based on either a retrospective medical record review 28 or individual organization's financial accounting review 25,29 .No studies estimated costs from a health system perspective, rather than costs incurred by hospitals only.In addition, none of the studies to date adopted a detailed micro-costing exercise and presented details of costing methodologies that should be adopted when undertaking costing studies 31 , particularly in relation to annuitization of costs and discounting.
There are several limitations of this study.Micro-costing provides a more accurate method of resource-use assessment in economic analyses of surgical interventions 23 .Despite the in-depth cost analysis undertaken using a whole National Health Service costing perspective, the sample size of the population for OSR (n = 35) was small relative to TEVAR (n = 115).This was due to the subsample of the ETTAA population being eligible with no recorded contraindication to either procedure in order to ensure a less-biased comparison.It was identified that the majority of patients in the ETTAA study who had an OSR procedure were not eligible for TEVAR, with the reasons reported elsewhere 11 .However, the main focus of micro-costing as a methodology is precision regarding the assessment of the economic costs of a healthcare intervention 15 and identifying key cost drivers.It has been highlighted that micro-costing studies vary widely in methodological and reporting quality, with a need to standardize methods and reporting of these studies and develop tools for their evaluation 32 .However, despite these debates in the health economics literature, sample sizes are not a research priority with a focus on accuracy and transparency.Given the detail and precision of our costing methodology, the cost estimates we present are likely to be representative of costs in routine clinical practice.
As reported previously 11 , it was clear that there were also differences in characteristics between the two surgical groups despite patients being eligible for both procedures.For example, TEVAR patients were older with smaller aneurysm size and more OSR patients had aneurysm extending into the aortic arch.Although the group included in this analysis are a subset of the larger ETTAA cohort study who were eligible for both OSR and TEVAR, there are still differences in anatomy between patients which may impact costs.Direct comparison between cohorts may result in possible bias as the sample sizes did not allow for control for potential confounding in costs.However, many of the resource inputs will be fixed in nature (for example, surgical equipment costs) and may not be strongly influenced by population characteristics or sample size.
The micro-costing methods and results presented in this study are of great value to help guide future research for the cost-effectiveness comparison of TEVAR versus OSR for treatment of distal arch/descending CTAA and are important to providers and decision makers for the purposes of developing guidelines.This study has identified and quantified the extent to which TEVAR procedure costs are driven by the high cost of endovascular stent graft and OSR procedure costs are driven by stay in critical care.Furthermore, this study has identified that NHS tariffs for TEVAR and OSR may be lower than the true cost of TEVAR and OSR procedures for the elective treatment of arch/descending thoracic aortic aneurysms, suggesting providers may not be adequately compensated.

Table 1 Baseline characteristics of patients who underwent endovascular stent grafting (TEVAR) or open surgical repair (OSR) and were eligible for both procedures
Data are presented as mean (s.d.) unless otherwise stated.*P of difference between TEVAR and OSR at baseline.

Table 2 Costs of resource use from index procedure until discharge for patients who underwent endovascular stent grafting (TEVAR) or open surgical repair (OSR)
All costs are reported in pounds Sterling (£) as mean (s.d.) unless otherwise noted.*EndovasculardeviceforTEVAR patients, surgical graft for OSR patients.†Criticalcarebeddays include intensive care unit and high-dependency unit.Gray et al. | 3with thoracoabdominal aneurysm repair having a very large overall cost £142 816 (£158 652).

Table 3 Subgroup analysis costs of resource use from index procedure until discharge
All costs are reported in pounds Sterling (£) as mean ± standard deviation unless otherwise noted.*Endovasculardevice for TEVAR patients surgical graft for OSR patients.†Criticalcare bed days include intensive care unit and high-dependency unit.

Table 4 Costs of NHS resource use from discharge to follow-up at 12 months for patients who underwent endovascular stent grafting (TEVAR) or open surgical repair (OSR)
All costs are reported in pounds Sterling (£) as mean (s.d.) unless otherwise noted.

Table 5 Subgroup analysis of costs of NHS resource use from discharge to follow-up at 12 months
All costs are reported in pounds Sterling (£) as mean (s.d.) unless otherwise noted.TEVAR = endovascular stent graft; OSR = open surgical repair.