Endovascular stents for abdominal aortic aneurysms: a systematic ...

DOI: 10.3310/hta13480 Health Technology Assessment 2009; Vol. 13: No. 48cost-effective compared with watchful waiting ordischarging the patient, taking account of age,fitness and aneurysm size.In this analysis we consider options for patientswho have poor operative fitness. Table 59 showedthat such patients aged 75 years with an aneurysmof 6.5 cm would have a probability of operativemortality with EVAR of 0.04 and with open repairof 0.12. This would put them on the marginsof eligibility for the EVAR trial 1 and EVARtrial 2. Current guidelines are unclear aboutthe management of these patients. All otherparameters are as in the base case.The results of the dynamic programme are shownin Table 74. At a threshold of £20,000 per QALY,EVAR would be cost-effective up to age 82.5 yearsfor an aneurysm of 8 cm and between 74 and 78years for an aneurysm of 6 cm. With base-caseassumptions, younger patients would be morecost-effectively treated with open repair, consistentwith Table 68. At £30,000 per QALY, EVAR wouldbe cost-effective up to 85 years for an aneurysm of8 cm and up to 80 years for an aneurysm of 6 cm.For patients with an aneurysm of 5 cm the modelpredicts that EVAR is cost-effective up to about78 years, with watchful waiting until 79 years.For patients with an aneurysm of 4 cm the modelpredicts that watchful waiting is cost-effective up to75.5 years if the aneurysm does not grow.DiscussionConventionally, patients have been classified asfit or unfit for open surgery, and AAA repair hasbeen offered to all patients fit for open surgerywith an aneurysm size of ≥ 5.5 cm. This chapterhas presented two models. The first examinedEVAR versus open repair in patients accordingto the conventional classification of fit for opensurgery and with large aneurysms of ≥ 5.5 cm. Thesecond explored the cost-effectiveness of differentpolicies concerning when, as well as how, surgeryshould be offered. In both models results havebeen presented by age, fitness and aneurysm sizeat diagnosis. Fitness in these models is defined ina general way so that a person of moderate fitnesswill have twice the operative mortality of a patientwith the same size of aneurysm and of the same agewith no pre-existing conditions.Summary of model results: patientsconsidered suitable for surgical repairThe base-case decision model found that EVARis not cost-effective on average for patients© 2009 Queen’s Printer and Controller of HMSO. All rights reserved.who are fit for open surgery, with an ICER of£49,000 per QALY and decision uncertainty thatEVAR might be cost-effective of 0.42. However,these assumptions are based on historical data,particularly the EVAR trial 1. First, as EVAR hasbecome more widely used, it is plausible that thecosts of the EVAR procedure, particularly the timespent in the intensive care unit and operatingtheatre, have fallen faster than those of open repairsince the start of the decade. This hypothesis isdifficult to test using observational data becausethe case mix of patients undergoing EVAR mayalso have changed over this period. Second, it isplausible that the EVAR trial 1 overestimates therelative rate of reinterventions of EVAR versus openrepair because it does not include late laparotomiesand it is now less common to reoperate on sometypes of endoleak. Third, and related to theprevious point, the frequency and cost of routinesurveillance after EVAR may have been diminishingin recent years. Under this more favourablescenario, EVAR has an ICER of £12,000 per QALYand a probability of being cost-effective of 0.74versus open repair at a threshold of £20,000 perQALY.The model also considered how cost-effectivenessmight vary by subgroups defined by age, aneurysmsize and fitness. If patients can be classified intogood, average and poor operative risk, then forpatients of most ages and aneurysm sizes, EVARis cost-effective compared with open repair inpatients of poor risk but not cost-effective inpatients of good risk. The absolute benefit of EVARcompared with open repair is low in patients ofgood operative risk. Furthermore, there is a longtermrisk of complications and reinterventions afterEVAR. The decision is very uncertain in patients ofmoderate risk.Summary of model results: managementof patients with poor or very poor fitnessCurrent UK clinical practice is that electivesurgery is generally recommended for patientswith aneurysms of ≥ 5.5 cm or with aneurysms> 4.5 cm that have increased in diameter by morethan 0.5 cm in the last 6 months. However, theseguidelines are based on the risks and benefits ofopen surgery and do not take account of costs.Neither do they take account of the findings of theEVAR trial 2, which called into question whetheraneurysm repair was effective for unfit patients.The decision model has been used to identify thecost-effective management of patients for whomEVAR is an option, according to age and aneurysmsize.131