Abdominal Aortic Aneurysms and Endovascular Repair

Detailed Information

 

Rupture of an abdominal aortic aneurysm (AAA) accounts for 10,000 deaths per annum in the United Kingdom(1). It occurs most commonly in men over the age of 65 (ratio 10 men to 1 woman), and is a disease of westernised societies. Rupture of an AAA can cause death from catastrophic blood loss. Approximately 50% of people with a rupture reach hospital alive and then undergo urgent surgery. Conventionally, this often involves a long midline incision from the xiphisternum  to the pubic bone. The aorta is then replaced by a piece of artificial vessel made from Dacron (polyester), sutured into place with non absorbable prolene or nylon. 50% of patients who have an emergency open operation will die because of complications after the surgery.

The disease is preventable. Aneurysm of the aorta can be detected by clinical examination or as part of a screening programme. AAA’s of greater than 5cm in diameter require prophylactic replacement(2) (3). In this elective situation, between 95% and 97% of patients will leave hospital after an inpatient stay of  between 10 days and two weeks(4). The size of the abdominal wound and disturbance of normal body function means that patients take between six weeks and three months to recover.

Recently, surgical research has been directed towards endovascular repair of the aorta. This procedure involves an incision in one or both groins to obtain access to the blood vessels supplying the legs. By passing a catheter through the femoral artery a specially designed aortic graft can be inserted from within the lumen of the aorta. Instead of sutures, the graft is held in place by a series of pins, or anchors called a stent, which are pushed into a normal part of the aorta by self expansion of the stent(5). The first insertion of this type of graft was reported in 1991 and although the technique is in its infancy over 300 patients have been treated in Nottingham, ( the most active unit in the Northern hemisphere, including the USA)(6). Patients can be discharged within a week of the operation and because the wounds are only 5 -10cm long, they return to normal activities within 2-3 weeks. There is evidence that the avoidance of aortic cross clamping when endovascular AAA repair is done reduces the myocardial, respiratory and gastrointestinal effects associated with open repair(7) (8). These factors, the size of the wound and the complexity of surgery is such that patients with severe cardiorespiratory disease, who would not normally be suitable for conventional repair can now have a potentially life threatening condition treated. The technique could prove useful for both  elective and emergency AAA repair. In the latter case there is the potential to reduce dramatically the associated morbidity and mortality(9). At Queen's Medical Centre, the development of the current endovascular aortic graft has involved a multi-disciplinary team approach. Each patient, whether referred from local practitioners or vascular surgeons from other parts of the United Kingdom passes through a series of assessments before the operation itself. Following traditional out-patient consultation and explanation of the technique, each patient has the anatomy of their aneurysm accurately measured by spiral computed topography (CT), intra-arterial angiography and three-dimensional reconstruction of the images.  From the CT  data a graft can be designed for each patient. These procedures involve two consultant vascular radiologists and one aneurysm co-ordinator. At the time of operation, a four man team is required to prepare the graft and perform deployment in addition to the routine theatre personnel for a major vascular case. The team consists of the aneurysm co-ordinator, a consultant surgeon, a consultant radiologist and surgical registrar or second consultant. Post operatively over 50% of cases, despite severe co-morbid cardiorespiratory disease, have been able to return directly to the ward without need for an intensive care bed.

 

Endovascular AAA repair is in its infancy with the first patients now only six or seven years on from their operations. There is still a need for technical refinement and reduction of associated complications. One of these is control of haemorrhage at the femoral arteriotomy site and another is the problem of endoleak. During conventional AAA repair, lumbar branches that arise from the aneurysm sac may ‘back-bleed’ into the open sac. These can be oversewn with a suture under direct vision. During endovascular repair, this manoeuvre is not possible. Persistent ‘back-bleeding’ into the aneurysm sac after endovascular repair appears to lead to continued enlargement of the sac and there is therefore an increased risk of aneurysm rupture. If blood passes around the stents at the upper or lower ends of the graft, then there is a similar, perhaps greater risk, of aneurysm rupture. This type of abnormal flow into the aneurysm sac after endovascular exclusion of the aneurysm is termed endoleak. Endoleak occurs in some 10-50% of cases of endovascular repair(10)(5)(11)(12). Research in Nottingham has shown a relationship between the presence of thrombus in the aneurysm sac, its location and persistent endo-leak. Prevention of flow in the aneurysm sac is essential to prevent the aneurysm from continuing to enlarge.    

Queens Medical Centre and University Hospital provides secondary medical care for a population of 1.5 million. The immediate population covered by Nottingham Health Authority is 630,000. Each year, approximately 200 patients are referred to one of the five consultant vascular surgeons with the diagnosis of AAA. Of these about 70 are offered and undergo prophylactic repair whilst another 40 have emergency surgery for ruptured aneurysm. The remainder have aneurysms that are too small to require repair, refuse operation or have aneurysms that would be difficult to repair without a high risk of mortality. These are followed up regularly with ultrasound to monitor symptoms and aneurysm growth.

 

 

 References

1.   Greenhalgh RM. Prognosis of abdominal aortic aneurysms. BMJ 1990;301:136.

 

2.   Cronenwett JL, Murphy TF, Zelenock GB, et al . Actuarial analysis of variables associated with rupture of small abdominal aortic aneurysms. Surgery 1985;98:472-83.

 

3.   Nevitt MP, Ballard DJ, Hallet JW. Prognosis of abdominal aortic aneurysms. N Engl J Med 1989;321:1009-14.

 

4.   Campbell WB. Mortality statistics for elective aortic aneurysms. Eur J Vasc Surg 1991;5:111-13.

 

5.   Marin ML, Veith FJ, Cynamon J, et al. Initial experience with transluminally placed endovascular grafts for the treatment of complex vascular lesions. Ann Surg 1995;222(4):449-469.

 

6.   Parodi JC, Palmaz JC, Burone TD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg 1991;5:491-499.

 

7.   El-Marasy NM, Yusuf SW, Lonsdale RJ, et al. Study of the Effect of Endovascular Aneurysm Repair on colonic perfusion. J Endovasc Surg 1996;3:80-122.

 

8.   Baxendale B, Baker DM, Hind R, et al. Haemodynamic changes during endovascular graft insertion for aortic aneurysms. Int Angiology 1995;14((Suppl 1)):247.

 

9.   Yusuf SW, Whitaker SC, Chuter TAM, Wenham PW, Hopkinson BR. Emergency endovascular repair of leaking aortic aneurysm. Lancet 1994;344:1645.

 

10. Murphy KD, Richter GM, Henry M, Encarnacion CE, Le VA, Palmaz JC. Aortoiliac Aneurysms: Management with Endovascular Stent-Graft Placement. Radiology 1996;198:473-480.

 

11. Blum U, Langer M, Spillner G, et al. Abdominal Aortic Aneurysms:Preliminary technical and clinical results with transfemoral placement of endovascular self expanding stent-grafts. Radiology 1996;198:25-31.

 

12. May J, White GH, Yu W, et al. Surgical management of complications following endoluminal grafting of abdominal aortic aneurysms. Eur J Vasc Endovasc Surg. 1995;10:51-59.

 

13. Boyle JR, McDermott E, Crowther M, Wills A, Bell PRF, Thompson MM. Doxycycline inhibits elastin degradation and metalloproteinase production in a model of aneurysmal disease. Br J Surg 1997;84:696-725.

 

14. Lanne T, Sonesson B, Bergqvist D, Bengtsson H, Gustafasson D. Diameter and Compliance in the Male Human Abdominal Aorta: Influence of age and Aortic Aneurysm. Eur J Vasc Surg 1992;6:178-184.