Expert Opinion - Abdominal aortic aneurysms

Endovascular repair in the treatment of aneurysms. By Miss Rachel Clough and Professor Peter Taylor.

CT scan showing an abdominal aortic aneurysm (Author Image)
CT scan showing an abdominal aortic aneurysm (Author Image)

Abdominal aortic aneurysms (AAA) affect 5 per cent of men over the age of 50. Women are affected less often than men (1:9). The majority of AAAs are asymptomatic until they rupture.

More than 90% of patients who rupture at home will die and only 50% of patients who have an operation will survive. In contrast, the mortality for elective surgery is less than 5% and because of this an AAA screening programme is being rolled out in England and Wales for men aged 65 years; screening is not necessary in women because significantly fewer are affected.

The annual risk of rupture in men is 3-15% with an AAA diameter of 5-5.9cm and between 10-20% for aneurysm greater than 6cm. There is some evidence that women may benefit from having their aneurysms treated at 5cm.

Surgical repair
Treatment of aneurysms has been revolutionised by endovascular repair. Open surgical repair of AAA was pioneered in the middle of the 20th century. The aneurysm is replaced by suturing a polyethylene synthetic graft inside the aneurysm sac, which is closed to prevent the bowel adhering to it. The mortality from open repair is approximately 5%. Complications, such as MI, cardiac arrhythmias, respiratory infections, incisional hernia and bowel obstruction, occur in 15-30% of patients.

In 1991, two pioneers, Volodos from the Ukraine and Parodi from Argentina, developed the technique of endoluminal repair. A metal stent is covered in graft material such as polyester or polytetrafluoroethylene.

The devices are restrained in sheaths which are introduced into the aorta via the common femoral artery. The stents are oversized by 10-20% compared with the normal segment of artery proximal and distal to the aneurysm.

These 'landing zones' need to be disease free, not tortuous and of sufficient length to provide secure fixation. Additional fixation of the device to the aortic wall is required in the form of barbs to prevent distal migration.

Aneurysms which do not have adequate landing zones can still be treated endovascularly but the long-term results will not be as durable as those treated within the manufacturers' recommendations for use.

Endoleaks
The term 'endoleak' is used to identify leaks around the device which are still contained within the aneurysm sac. Type I refers to problems with the proximal and distal fixation and type III refers to disconnection of device components.

Type II endoleaks are due to patent branch vessels such as the inferior mesenteric artery, the lumbar arteries or the median sacral artery.

Types I and III require urgent attention as the aneurysm is exposed to arterial pressure and at risk of rupture. Type II endoleaks are not treated unless the aneurysm sac is increasing in diameter.

Evidence
We now have good long-term data from RCTs comparing open with endovascular repair of AAA. The endovascular aneurysm repair (EVAR) trials are multicentre trials which show that endovascular repair is safer than open surgery with a 3% lower peri- operative mortality.

Endovascular repair is associated with other beneficial outcomes, such as less blood loss, shorter hospital stay, less requirement for intensive and critical care beds and an earlier return to normal activities. The 3% benefit in terms of aneurysm-related deaths disappears with time, and at eight years, 54 per cent of patients are alive in both groups.

Endovascular repair has been widely adopted in large vascular centres. However, long-term results from the RCTs raise some doubts about the durability of endovascular repair.

The number of complications and secondary procedures is higher with endovascular repair compared with open surgery. These results are confirmed by the Dutch DREAM trial.

More worryingly, there is a steady increase in the number of patients presenting with a ruptured AAA after the EVAR trials, raising questions over the durability of devices.

It is therefore essential that endovascular repair patients continue to have surveillance to detect problems before their aneurysm ruptures.

In contrast, patients who have open repair have a very low rate of aneurysm rupture and usually require no surveillance.

EVAR II trial
Patients medically unfit for open surgery were randomised in the EVAR II trial to either endovascular repair or surveillance with no treatment. At eight years, 70% of the endovascular repair group and 74% of the surveillance group had died.

The conclusions were that endovascular repair was of no benefit for patients unfit for open repair. However if their fitness could be improved such that their life expectancy can be extended then they could be candidates for repair, as endovascular repair was effective in preventing aneurysm related death.

The IMPROVE trial is a multicentre UK RCT comparing EVAR with open repair for ruptured AAA, and is currently recruiting.

Conclusions
Each patient should be individually assessed as to their operative risk and life expectancy before treatment.

Elderly patients with a reasonable life expectancy should have endovascular repair as long as they are anatomically suitable, and accept they will require lifelong surveillance.

Fit young patients who have a low operative risk and a long life expectancy should have open repair as this offers a durable solution which does not require surveillance. Patients unfit for open repair who have a short life expectancy do not benefit from intervention.

  • Miss Clough is an NIHR BRC clinical training fellow and Professor Taylor is a professor of vascular surgery, Guy's and St Thomas' NHS Foundation Trust

Resources
1. The United Kingdom Small Aneurysm Trial Participants. N Engl J Med 2002; 346: 1445-52.

2. Bown MJ, Sutton AJ, Bell PR et al. Br J Surg 2002; 89: 714-30.

3. The United Kingdom EVAR Trial Investigators. N Engl J Med 2010; 362: 1863-71.

4. The United Kingdom EVAR Trial Investigators. N Engl J Med 2010; 362: 1872-80.

5. Dream Study Group. N Eng J Med 2010; 362: 1881-9.

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