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

Background2in patients with aneurysms of < 5.5 cm diameter.Current guidelines recommend that patients withasymptomatic aneurysms < 4.5 cm are followedup with ultrasonography every 6 months, whereasaneurysms of 4.5–5.5 cm are followed up every 3 or6 months.Approximately 25% of patients with an AAArequiring surgery are considered unfit foropen surgery. 9 Such patients will be kept undersurveillance with an option to defer surgery or adecision to rule out surgery entirely. As age, fitnessand the untreated risk of rupture are evolvingover time, the option to defer makes the decisioncomplex and dynamic. 10,11 It is unclear what theoptimum management policy should be in patientsconsidered unfit for open surgery. It may be thata policy whose aim is to try and improve patientfitness might be effective and patients may beoffered medical therapy to reduce risk factors, forexample smoking cessation and blood pressurereduction therapy, but such a policy has not yetbeen evaluated.Description of technologyunder assessmentEndovascular aneurysm repair (EVAR) is aminimally invasive technique that involves placinga stent graft prosthesis at the site of the aneurysm. 12The stent graft is inserted through a small incisionin the femoral artery in the groin, carried to thesite of the aneurysm using catheters and guidewiresand placed in position under radiographicguidance. Once in position the stent graft isdeployed and anchored to the wall of the aortausing a variety of fixing mechanisms. The graftis stronger than the weakened aorta and allowsblood to pass through it without creating pressureon the aneurysm. The main types of endovascularstent grafts are aortic tube grafts (no longer usedin the UK), aorto-uni-iliac grafts and aorto-bi-iliac(bifurcated) grafts, with most procedures in theUK using bi-iliac stents. EVAR is carried out undergeneral, regional or local anaesthesia.EVAR has been used to treat patients both classifiedas fit for open repair and classified as unfit. It isused both as an elective procedure and to treatsymptomatic and ruptured aneurysms. However, itmust be emphasised that EVAR is not suitable forall patients. Patient suitability for EVAR dependson the morphology of the aneurysm. This isassessed by diagnostic imaging, usually computedtomography (CT) scanning and occasionallyangiography or magnetic resonance imaging(MRI). In an unselected population of patientswith AAA only 55% did not have an absolutemorphological contraindication to EVAR. 13Potential advantages of EVAR over open repairinclude reduced time under general anaesthesia,elimination of the pain and trauma associated withmajor abdominal surgery, reduced length of stay inthe hospital and intensive care unit, and reducedblood loss. 14 Potential disadvantages include thedevelopment of endoleaks, which occur whenblood continues to flow through the aneurysmbecause the graft does not seal completely orbecause of backfilling of the aneurysm from othersmall vessels arising from the aneurysm wall. Thus,although open repair does not require any specialfollow-up, patients who have undergone EVARrequire regular CT scans to check for the presenceof late endoleaks. 14 In addition, if the EVARprocedure is unsuccessful or complications ariseduring the procedure, conversion to open repairmay be necessary in patients initially consideredunfit for open surgery. 14Prices of endovascular stent graftsEndovascular stents are not homogeneousproducts. There are a number of differentendovascular stent devices made by differentcompanies, each with different costs. This is furthercomplicated by the fact that different patientswho may be fitted with the same company’s devicemay require different numbers of extensions. Thecompanies who produce these devices also offerdifferent pricing structures (e.g. some charge aprice per patient regardless of the number ofextensions required whereas others charge basedon the parts required). If the price per patientis not fixed then ideally the mean price per caseshould be calculated based on an assessment ofthe expected number of extension parts required,which in turn depends on the population casemix. There is also the added complication thatindividual hospitals often do not actually pay thelist price, with manufacturers offering discounts.These considerations make the process of costing adevice for the economic evaluation complex.The NICE Guide to the Methods of TechnologyAppraisal 15 states that: ‘Where the actual price paidfor a resource may differ from the public list price(for example, pharmaceuticals, medical devices),the public list price should be used’.Commercial-in-confidence information on theprice of different models of stent grafts andacademic-in-confidence information on the use