The UK Small Aneurysm Trial had already shown that early, prophylactic elective surgery does not improve five-year survival among patients with small abdominal aortic aneurysms. However, when active follow-up of the UK Small Aneurysm Trial was closed in June 1998, only 305 of the 1,090 patients had died (28%). It was therefore decided to undertake a further analysis when 100 surviving patients would have reached nine years of follow-up and approximately half of the original cohort would have died.
Professor Roger Greenhalgh, the lead applicant of the UK Small Aneurysm Trial, with Professor Janet Powell and Professor Vaughn Ruckley, presented the results of this long-term survival analysis at the 24th Charing Cross International Symposium and the paper was published in the New England Journal of Medicine in May along with a covering editorial.
After nine years the mean survival both in patients initially randomised to early surgery and those to surveillance were very similar, although the overall survival was marginally higher for patients randomised to early surgery. The mean duration of survival was 6.5 years among patients in the surveillance group, compared with 6.7 years among patients in the early surgery group.
Commenting on the long-term analysis, Greenhalgh said: “We must be cautious, the data showed weak benefit for early surgery only at the eight year assessment point, not at two, four or six years. The explanation for this weak benefit could lie in lifestyle changes in those who had early major surgery – but that is pure speculation.
In the trial, of the 1,090 who consented to undergo randomisation, 563 were assigned to undergo early elective surgery and 527 to undergo ultrasonographic surveillance. By the end of the trial (30 June, 1998), 520 of the patients in the early-surgery group and 327 of those in the surveillance group had undergone surgical repair of an abdominal aortic aneurysm. A total of 289 patients in the surveillance group had undergone surgery according to protocol; in the other 38 patients, the repair represented a protocol violation.
Treatment between the end of the trial and August 2001 did not necessarily adhere
to the initial trial protocol, and an increasing proportion of the patients underwent endovascular repair of the aneurysm.
About one fifth of the patients in the surveillance group (105 of 527) died without having undergone repair of the aneurysm.
By August 2001, a mean follow-up of eight years, there had been 254 deaths in the surveillance group and 242 in the early-surgery group. The adjusted hazard ratio for death from any cause in the early-surgery group as compared with the surveillance group was 0.83 (95% confidence interval, 0.69 to 1.00; P=0.05). Survival was initially worse in the early-surgery group and subsequently worse in the surveillance group; the survival curves crossed at about three years.
There was no evidence that age, sex or the initial size of the aneurysm modified the hazard ratio. Patients who reported current smoking had a higher risk of death than did former smokers, and the rate of early cessation of smoking was higher in the early-surgery group than in the surveillance group.
The total rupture rate (including non-fatal ruptures) was 1.6% per year before June 1998 and 3.2% per year between July 1998 and August 2001.
Death was attributable to a ruptured aneurysm in 19 of the 411 men who died and in 12 of the 85 women who died. The high risk of abdominal aortic aneurysm rupture in women, about four times that in men, suggests that an upper limit for surveillance of an aneurysm diameter of 5.5cm is too high in women.
The final message that the comes out of the UK Small Aneurysm Trial is that there is no difference in terms of life years gained whether surgery is done at once or left until the aneurysm grows to 5.5cms. Therefore the six-year findings, from 1998, that there is no benefit in early surgery are upheld by the long-term outcomes.