AAA Stent–Grafts: Past Problems and Future Prospects MITAL DESAI, 1 JAMES EATON-EVANS, 2 CLAIRE HILLERY, 2,5 RAHELEH BAKHSHI, 1 ZHONG YOU, 2 JIAN LU, 3 GEORGE HAMILTON, 1,4 and ALEXANDER M. SEIFALIAN 1 1 Division of Surgery & Interventional Science, Centre for Nanotechnology & Regenerative Medicine, University College London, London, UK; 2 Department of Engineering Science, University of Oxford, Oxford, UK; 3 Biological Physics Group, The University of Manchester, Manchester, UK; 4 Vascular Unit, Department of Surgery, Royal Free Hampstead NHS Trust Hospital, London, UK; and 5 Medtronic, Galway, Ireland, UK (Received 21 October 2009; accepted 31 January 2010; published online 17 February 2010) Associate Editor Jane Grande-Allen oversaw the review of this article. Abstract—Endovascular aneurysm repair (EVAR) has quickly gained popularity for infrarenal abdominal aortic aneurysm repair during the last two decades. The improve- ment of available EVAR devices is critical for the advance- ment of patient care in vascular surgery. Problems are still associated with the grafts, many of which can necessitate the conversion of the patient to open repair, or even result in rupture of the aneurysm. This review attempts to address these problems, by highlighting why they occur and what the failings of the currently available stent grafts are, respec- tively. In addition, the review gives critical appraisal as to the novel methods required for dealing with these problems and identifies the new generation of stent grafts that are being or need to be designed and constructed in order to overcome the issues that are associated with the existing first- and second- generation devices. Keywords—Abdominal aortic aneurysm, Stent–graft, Endo- vascular repair, Medical devices, Vascular. INTRODUCTION Abdominal aortic aneurysm (AAA) occurs when weakened areas of abdominal aortic wall result in bal- looning of the blood vessel. An AAA is defined as an enlargement of the aorta of at least 1.5 times its normal diameter or greater than 3 cm diameter in total. AAAs are more commonly located in an infrarenal position. Attributed risk factors include increased age, smoking, atherosclerosis, and hypertension. 3 AAAs are about three times more common in men than in women. They account for 1.81% of deaths in people over the age of 65 years in England and Wales, with an incidence of 3.5 new aneurysms occurring for every 1000 person years. 18 Most AAAs are detected incidentally during clinical investigation (e.g., ultrasound or X-ray) for other conditions. Because most AAAs are asymptomatic, it is difficult to estimate their prevalence, but screening studies in the UK have estimated a prevalence of 1.3– 12.7% depending on the age group studied. 44 The incidence of symptomatic AAA in men is approxi- mately 25 per 100,000 at age 50, increasing to 78 per 100,000 in those older than 70 years. 44 The imple- mentation of a national screening program for AAA is under way and the first centers started screening in March 2009. The remaining centers will be managed in a phased roll-out over the next 5 years. Symptoms that can occur as an aneurysm enlarges include a pulsating sensation in the abdomen, back pain, and abdominal pain that may spread to the back. Patients with a symptomatic AAA need rapid medical attention. Among patients with a ruptured AAA the mortality rate is about 80% which increases up to 90% when in-hospital deaths are included. 79 Even when they undergo emergency surgery, only about half sur- vive beyond 30 days. It has long been established that, for large aneurysms at least, prophylactic measures are required to prevent aneurysm rupture 18 and one in three aneurysms will rupture if left untreated. 37 The risk of rupture increases with the size of the aneurysm, and those aneurysms larger than 6 cm in diameter have an annual risk of rupture of 25%. Several studies indicate that without surgery the 5-year survival rate for patients with aneurysms larger than 5 cm is about 20%. 44 In current UK clinical practice, elective surgery is generally recommended for Address correspondence to Alexander M. Seifalian, Division of Surgery & Interventional Science, Centre for Nanotechnology & Regenerative Medicine, University College London, London, UK. Electronic mail: A.Seifalian@ucl.ac.uk Annals of Biomedical Engineering, Vol. 38, No. 4, April 2010 (Ó 2010) pp. 1259–1275 DOI: 10.1007/s10439-010-9953-1 0090-6964/10/0400-1259/0 Ó 2010 Biomedical Engineering Society 1259