3. Endoluminal Treatment of Infrarenal Abdominal Aortic Aneurysm

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1 3. Endoluminal Treatment of Infrarenal Abdominal Aortic Aneurysm Hence J. M. Verhagen, Geoffrey H. White, Tom Daly and Theodossios Perdikides A 78-year-old male was referred for investigation and management of an asymptomatic 6.2-cm diameter abdominal aortic aneurysm (AAA), which was diagnosed coincidentally during an abdominal ultrasound examination performed for investigation of prostatic symptoms. The patient had a significant previous medical history, which included ischaemic heart disease, severe chronic obstructive lung disease, and several previous laparotomies. He had undergone coronary artery bypass graft (CABG) surgery a few years ago. On examination, the patient was haemodynamically stable with no abdominal complaints. There was an expansile pulsatile mass palpable in his obese abdomen, and all peripheral pulses were palpable. Endoluminal repair of the AAA was considered, particularly in view of his high risk for open surgical repair. Question 1 What is the optimal method of preoperative aneurysm assessment? A. Abdominal colour flow duplex ultrasound. B. Contrast-enhanced spiral computed tomography (CT) scan of the abdomen. C. Abdominal colour duplex ultrasound and calibrated aortic angiography. D. Contrast-enhanced spiral CT scan of the abdomen and calibrated aortic angiography. Question 2 What is the mean annual risk of rupture of a 6.2-cm abdominal aortic aneurysm? A. Less than 5 per cent. 23

2 24 Vascular Surgery B. Between 5 and 10 per cent. C. Between 10 and 20 per cent. D. Greater than 20 per cent. Question 3 In anatomically similar aneurysms: A. Open repair is a safer option for high-risk patients. B. The benefits of endoluminal repair, in terms of reduced morbidity and mortality, only apply in high-risk patients. C. The presence of chronic renal failure is an absolute contraindication to endoluminal repair. D. Endoluminal repair results in a two-thirds reduction in 30-day operative morbidity and mortality compared to open aneurysm repair. A contrast-enhanced spiral CT scan was obtained, which demonstrated that endovascular repair of the AAA was possible (Fig. 3.1). A calibrated aortic angiogram was performed to better define some of the anatomical features (Fig. 3.2). This showed an infrarenal aneurysm with a maximum diameter of 62 mm. The neck of the aneurysm was 19 mm in diameter and 22 mm in length. The distance from the lowest renal artery to the aortic bifurcation was 125 mm, and there was a further distance of 60 mm from the aortic bifurcation to the orifice of the internal iliac artery on each side. The neck of the aneurysm was noted to be quite angulated. The common iliac arteries were non-aneurysmal but severely tortuous, with angulations of more than 90 in their midsection. The minimum diameters of the external iliac and femoral arteries were 9 mm bilaterally. An endoluminal repair procedure was planned. Question 4 Which anatomical features limit endoluminal repair? A. Length and diameter of the aneurysm neck. B. Length and diameter of the aneurysm. C. Angle of the neck as well as the angle of the iliac arteries. D. Tortuosity and diameter of the iliac arteries. Question 5 For choosing a suitable endoluminal graft, one must: A. Take the graft that resembles your measurements most closely.

3 Endoluminal Treatment of Infrarenal Abdominal Aortic Aneurysm 25 a b Fig (a,b)

4 26 Vascular Surgery c Fig a Contrast-enhanced CT scan at the level of the neck of the aneurysm, immediately below the renal arteries. The neck has a maximum diameter of 19 mm on this image and has no irregular features, such as mural thrombus or atheromatous plaque. b Contrast-enhanced CT scan at the level of the sac of the aneurysm, showing a typical target appearance due to the presence of significant mural thrombus lining the aneurysm and contrast filling the flow channel. Maximum diameter 62 mm. c Contrast-enhanced CT scan at the level just below the aortic bifurcation, showing two iliac arteries of diameter mm. d Three-dimensional reconstruction of a contrast-enhanced CT scan, showing angulation between the neck and the aneurysm of about 45. The iliac arteries are tortuous, with an angulation of at least 90. d

5 Endoluminal Treatment of Infrarenal Abdominal Aortic Aneurysm 27 a b Fig a Calibrated aortic angiogram showing the aortic lumen, renal arteries and neck of the aneurysm. b Calibrated aortic angiogram showing the lumen of the aorta and both iliacs. Note that the diameter of the iliac arteries measures less on the angiogram than on the CT images.

6 28 Vascular Surgery B. Oversize all diameters by 10 per cent. C. Oversize the proximal diameter by 20 per cent and the limb diameters by 10 per cent. D. Undersize all diameters by 10 per cent and balloon-expand them to the proper size at the end of the procedure. Due to the patient s severely impaired lung function and other risk factors, the procedure was performed under epidural anaesthesia. The abdomen and both groins were prepared into a sterile field. Common femoral arteries were surgically exposed, sheaths were inserted, and wires were put into place under fluoroscopy. Angiography was performed to mark exactly the position of the renal arteries (Fig. 3.3), and an endoluminal device was implanted successfully (Fig. 3.4). Question 6 Whilst deploying the graft, the following need to be considered: A. The orientation of the graft. B. The location of any renal accessory renal arteries. C. The location of the aortic bifurcation. D. The location of the bifurcation of the common iliac artery. Fig Early on-table angiogram to locate precisely the renal arteries during graft implant procedure. The arrow indicates the left renal artery. The device is ideally placed immediately below the orifice of the renal artery (note that some designs of endograft incorporate a bare stent that projects over the renal orifices).

7 Endoluminal Treatment of Infrarenal Abdominal Aortic Aneurysm 29 Fig Angiogram of a successfully deployed graft showing patent renal arteries, the endograft on the outside of the contrast-filled lumen, and the absence of an endoleak (flow of blood into the AAA sac). The blush near the proximal end of the graft (arrow) is gas inside the superimposed intestine. Question 7 What are the more common complications of endoluminal aneurysm repair? Question 8 Which of the following is the most important finding on follow-up imaging A. No change to the lung field on chest X-ray. B. The diameter of the aneurysm compared to the original diameter. C. The absence of a type II endoleak previously visible on CT. D. The position of the graft on abdominal X-ray. Commentary AAAs are generally a disease of elderly white males. In men, AAAs start to occur at the age of 50 years, reaching a peak incidence of about 350/100,000 person-years by the age of 80 years. The prevalence of AAAs of at least 3 mm in diameter in men over 65 years is 7.6 per cent. In women, AAAs tend to occur a few years later in life. The age-adjusted incidence is four to six times higher in men than in woman. Age,

8 30 Vascular Surgery gender and smoking are the risk factors with the largest impact on AAA prevalence [1]. Although ultrasonography is the method of choice for population screening or follow-up measurements in patients with known aneurysms, ultrasound imaging alone gives insufficient information for preoperative assessment for repair procedures. For open repair, most surgeons recommend a preoperative imaging study with (spiral) CT scanning, which provides accurate information regarding aneurysm size and its relationship to branch vessels, as well as any anatomic anomalies [2]. Preoperative imaging is even more important when endovascular treatment is considered, because patient selection and sizing of the endograft depend on it. With contrast-enhanced spiral CT, the dimensions of the proximal neck can be determined accurately and the presence of calcification or mural thrombus noted. Although the anatomy of the iliac arteries and accessory renal arteries can be demonstrated by spiral CT, in most medical centres calibrated aortography is also performed to allow accurate measurements. Anteroposterior and lateral views are required to demonstrate tortuosity in the neck of the aneurysm and the iliac arteries [3]. Three-dimensional reconstructions of contrast-enhanced CT scans are being utilised increasingly in order to get a more detailed perception of the actual anatomy. These reconstructions may become the standard method for accurate sizing of endografts in the near future. [Q1: D] The decision of whether to treat an AAA remains a difficult process in which multiple factors play a role. One important factor is the risk of rupture, which, unfortunately, will always be an estimate, since large numbers of patients with AAAs have not been followed up without intervention. Based on currently available data from the UK Small Aneurysm Trial, the annual risk of rupture is less than 1 per cent when the diameter is cm, although the validity of this risk estimation was compromised by the fact that many patients in this trial received surgery at a diameter less than 5.5 cm due to other factors. With increasing diameters, the annual rupture rates have been estimated to be as follows: 5 6 cm, 5 15%; 6 7 cm, 10 20%; 7 8 cm, 20 40%; <greater than>8 cm, 30 50% [4]. [Q2: C] Recent trials have demonstrated a reduction in 30-day morbidity and mortality rate in patients undergoing endoluminal aortic aneurysm surgery compared to the traditional open approach [5, 6]. These well-constructed randomised trials showed a reduction of approximately 65 per cent in the incidence of moderate to major complications following endoluminal repair compared to open repair. Current information indicates that the benefit is likely to be greater for high-risk patients. The presence of renal failure is not an absolute contraindication to the endovascular approach as various precautions can be taken to protect the kidneys, such as intravenous hydration, antioxidant medications or temporary dialysis. The average contrast use for the procedure is ml. [Q3: C, D] Not all aneurysms are anatomically suitable for endovascular repair. In general, all endoluminal grafts need areas of reasonably healthy vessel wall proximally and distally to be able to seal off the aneurysm from the blood flow. Most important for suitability are the size and morphology of the proximal neck (the segment of aortic wall between the lowest renal artery and the beginning of the aneurysm). The neck should consist of relatively normal aorta over a length of at least 1.5 cm, and the diameter should not exceed 30 mm. Another limitation for endovascular repair is the maximum angulation in the neck (should not exceed 60 ) and the iliac arteries (ideally less than 90 ) [7]. [Q4: A, C, D]

9 Endoluminal Treatment of Infrarenal Abdominal Aortic Aneurysm 31 After precise measurements from angiography and CT scanning, the optimal size of the graft can be chosen. To anchor the proximal part of the graft firmly onto the native aortic wall, a constant radial force of the graft is necessary. To achieve this, it is important to oversize the graft. Unfortunately, some recent reports suggest that there may be slow ongoing expansion of the neck of the aneurysm after endoluminal AAA repair [8]. This may favour a more aggressive oversizing of the proximal part of the graft, but this could in turn cause infolding of the graft fabric, which may lead to failure to seal the AAA sac ( endoleak ). Current recommendations are to oversize the proximal part of the graft by per cent and the limb diameters by 10 per cent. [Q5: C] Most current devices for endovascular repair procedures depend on self-expanding stents or wireforms for attachment to the aortic wall. Most grafts are configured so that there is a marking indicating the contralateral limb. Preoperative measuring assessment of size is confirmed intraoperatively to prevent problems in length of the limbs. After the graft has been implanted, a pigtail angiographic catheter is reintroduced, and a post-procedure digital subtraction angiogram is performed. The contrast run is examined closely for the presence of extravasation of contrast, suggesting an endoleak. In some grafts, the aneurysmal sac will fill temporarily with contrast due to porosity of the graft material. A retrograde angiogram through the femoral sheaths is used to visualise a seal at the distal end of the graft. [Q6: A, B, C, D] Complications of endoluminal AAA repair have been divided into remote/systemic and local/vascular. The remote/systemic complications are similar to, but less frequent than, those occurring after open AAA repair. The local/vascular complications are more specific for the endoluminal repair (Table 3.1). [Q7] The follow-up of endoluminal aneurysm repair patients remains important in determining the long-term success of aneurysm exclusion. General recommendations include a physical examination and abdominal X-ray (AXR) plus contrastenhanced CT scan within 1 week, then 6, 12 and 18 months after operation, and then annually. At present there are a number of registries such as Cleveland Clinic, and a European collaboration (EUROSTAR) [9] indicating an annual mortality rate of more than 1 per cent related to abdominal aortic aneurysms after endovascular repair of AAA (EVAR). It appears that per cent of deployed grafts will require some secondary intervention. The requirement for secondary intervention is greater for earlier generation grafts, compared with the newer devices. This appears Table 3.1. Local/vascular complications after endoluminal repair Injury to access arteries Embolisation Distal ischaemia Renal failure Endoleak Type I (proximal or distal attachment zones) Type II (lumbar or mesenteric collateral channels) Type III (fabric tear or modular dislocation) Type IV (porosity leak) Endotension Graft limb thrombosis Groin wound infection Conversion to open repair

10 32 Vascular Surgery to be independent of the length of time the grafts remain in place. There is, however, significant improvement in quality-of-life measurements in patients with EVAR compared with open repair up to at least 6 months [10]. The importance of the type II endoleaks is unclear. However, they have been known to reappear after a period of absence. The position and the integrity of the graft is easily identified on plain abdominal X-ray. Whilst the aneurysmal sac can vary over time with endovascular repair, an expanding aneurysmal sac in the presence or absence (endotension) of endoleaks warrants further investigation and treatment. [Q8: B] Case Analysis Quiz A number of imaging examples are shown in Figs Analyse the anatomical suitability of each case for the possibility of endoluminal graft repair of the AAA. In particular, determine the favourable and unfavourable features shown. Fig Aortic angiogram showing a very favourable anatomy for endovascular repair: the neck is straight and long, without irregular features of the wall. In addition, the aneurysm sac is straight, and both iliac arteries are non-aneurysmal and relatively straight.

11 Endoluminal Treatment of Infrarenal Abdominal Aortic Aneurysm 33 Fig In this case, the aortagram shows neck angulation of about 45, and the neck has a reversed taper configuration. Both these features are considered to be unfavourable for endoluminal treatment because it is more difficult for the device to achieve complete seal and reliable fixation). a b Fig Three-dimensional reconstruction of contrast-enhanced CT scan showing severe iliac angulation: a lateral view, b antero-inferior view. The iliac arteries show angulation in at least three different planes. The right common iliac artery is also aneurysmal. These features are unfavourable for access of the deployment sheath, and are associated with a higher risk of distal endoleak.

12 34 Vascular Surgery Fig Aortic angiogram showing a 90 angulation within the neck of the aneurysm. This is considered to be unsuitable for endovascular repair, since it is difficult to achieve satisfactory seal of the AAA sac or long-term attachment of the device. References 1. Melton LJ 3rd, Bickerstaff LK, Hollier LH, Van Peenen HJ, Lie JT, Pairolero PC, et al. Changing incidence of abdominal aortic aneurysms: a population-based study. Am J Epidemiol 1984;120: Jaakkola P, Hippelainen M, Farin P, Rytkonen H, Kainulainen S, Partanen K. Interobserver variability in measuring the dimensions of the abdominal aorta: comparison of ultrasound and computed tomography. Eur J Vasc Endovasc Surg 1996;12: Fillinger M. Computed tomography and three-dimensional reconstruction in evaluation of vascular disease. In: Rutherford RB, editor. Vascular surgery, 5th edn. Philadelphia: WB Saunders, 2000; Rutherford RB, editor. Vascular surgery, 5th edn. Philadelphia: WB Saunders, Greenhalgh RM, Brown LL, Kwong GP, Powell JJ, THompson SG. Comparison of endovascular repair with open repair in patients with AAA (EVAR trial 1) 30 day operative mortality results: randomised controlled trial. Lancet 2004;364: Prinssen M, Verhoeven ELG, Buth J, Cuypers PW, van Sambbek MR, Balm R, et al. A randomized trial comparing conventional and endovascular repair of abdominal aortic aneurysms. N Engl J Med 2004;351: Ahn SS, Rutherford RB, Johnston KW, May J, Veith FJ, Baker JD, et al. Reporting standards for infrarenal endovascular abdominal aortic aneurysm repair. J Vasc Surg 1997;25: Prinssen M, Wever JJ, Mali WP, Eikelboom BC, Blankensteijn JD. Concerns for the durability of the proximal abdominal aortic fixation from a 2-year and 3-year longitudinal computed tomography angiography study. J Vasc Surg 2001;33:S Van Marrewijk CJ, Buth J, Harris PL, Norgren L, Nevelsteen A, Wyatt MG. Significance of endoleaks after endovascular repair of abdominal aneurysms: the EUROSTAR experience. J Vasc Surg 2002;35: Prinssen M, Buskens E, Blankensteijn JD, DREAM trial participants. Quality of life after endovascular and open AAA repair. Results of a randomised trial. Eur J Vasc Endovasc Surg 2004;27: