ABDOMINAL AORTIC ANEURYSMSPart 2: Treatment.1) Medial ManagementTwo agents have been identified in animal studies as being of potential clinical benefit. Propranolol seems to increase the tensile strength of connective tissue and reduces expansion rate of AAAs Doxycycline, a metalloproteinase inhibitor can inhibit the proteolytic process found in the aneurysm walls.
2) Surgical ManagementA) Who should undergo surgical repair? On the symptomatic side, clearly patients who have ruptured AAAs and those with documented AAAs with associated abdominal, or back pain need surgical intervention. For asymptomatic AAAs the British Small Aneurysm Trial found that once an AAA has reached 5.5cm in diameter that the risk benefit ratio favours surgical repair. Other AAAs that merit repair even if they are not yet larger than 5.5cm are those growing by lcm or more per year and patients with a strong family history of AAA rupture. b) Modalities of repair Minimally Invasive Repair.This is also called endoluminal repair, or stent grafting of a an aortic aneurysm and was introduced in 1991. Endoluminal AAA repairs can be done in any patient with a suitable AAA. It is, however, particularly, attractive for patients with significant comorbidity - cardiac, respiratory and renal. Because we do not know about the long term durability of these grafts most Vascular Surgeons would tend not to use them in younger patients.
Not all AAA are suitable for endoluminal repair. The two factors that determine this are the neck of the aneurysm and the iliac arteries. The neck is that part of the aorta between the renal arteries and the
SAC. It is where the top of the graft engages the aorta and is crucial to the stability of the graft and a successful seal between the graft and the aorta. It should be at least 15mm long and preferably not greater than 30mm wide, not bell shaped and not excessively
angulated in relation to the sac (Fig 1) Acute angulation pre-disposes to a leak between the graft and the aorta (endoleak) (Fig 2). Tortous and calcified iliac arteries may make graft deployment difficult and hazardous as the delivery system is fairly rigid (Fig 2).
Most commercial grafts are made up of a self-expanding metal skeleton (Nitolol) covered with graft material. The graft is mounted on a deliverv rod approximately the diameter of a pencil and kept in place by a sheath over it. The graft is deployed by pulling back the sheath and the graft expands - like opening an umbrella. The attraction of the endoluminal graft is that it can be deployed by a small incision in each groin. The main graft is passed on its delivery rod up one iliac artery until it is just below the renal arteries (performed under radiological screening) and then deployed. The passenger limb is passed up the other iliac artery and docks with the main graft. The whole graft thus goes from the neck of the aneurysm to the iliac arteries. Stent grafting is also used for thoracic aneurysms. InvestigationsThe Authors use a spiral CT scan (Figs 1 & 2) to assess suitability for endoluminal grafting and to measure the geometry of the aneurysm so that the endograft can be built to suit the patient. Routine CT scans and angiograms can also be used. ProblemsThe main problem with endoluminal grafts are endoleaks mainly at the neck, or the iliac arteries. The
incidence of this is approximately 2-15%. Endoleaks can pre-dispose to rupture as the sac is still exposed to the
blood pressure. They can be treated with additional stents.
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