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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. |