12-year UK SAT results justifies surveillance policy

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UK AAA screening programme supported by Vascular Society

The results from two studies presented at this year’s annual meeting of the Vascular Society in Edinburgh, Scotland, will be a welcome boost for the supporters of a national AAA screening programme in the UK. Twelve-year follow-up from the United Kingdom Small Aneurysm Trial (UK SAT) and mid-term estimate of mortality benefit and cost-effectiveness for AAA screening from the Multicentre Aneurysm Screening Study (MASS), both underlined the benefits and necessity of a UK AAA screening programme.

The news comes as the Screening AAAs Very Effectively (SAAAVE) Act begins in the United States. This Act will take the form of an ultrasound scan as part of the one-time ‘Welcome to Medicare’ physical exam that is available to all 65 year olds who join Medicare each year, including men who smoke and those with a history of aneurysms. Only new entrants to Medicare part B will be screened – seniors who have already had their ‘Welcome to Medicare’ physical exam will not be retrospectively screened.

In November 2006, a statement from the National Screening Committee (NSC) said that its Working Group “should continue its task of developing a plan for a National AAA screening programme.” This plan would consist of an overarching framework, a set of standard operating procedures and a commissioning framework. The intention is for this plan to be presented to the next meeting of the AAA Working Group in January 2007.

Mr Alan Scott, Chichester, UK, discussed the issue surrounding a national screening programme at the meeting in Edinburgh. He commented that requirements for screening would need a population of approximately 800,000 and vascular units committed to the standards for treatment of screen detected AAA. He added that roll out is likely within two years.

The NSC has reconfirmed that AAA screening could be offered to men aged 65, provided that the men invited were given clear information about the risks of elective surgery. Scott also warned that steps be taken to create networks of vascular surgical services to allow further specialisation, bigger throughput and therefore lower risk, because of the evidence relating to volume and quality. However, it is uncertain and for debate whether the programme should revolve around a general practitioners surgery or be separate in the community, the NSC has said it will decide on this. The Committee is also aware of the downsides of screening in that there is increased concern associated with screening.

Next, Dr Jonothan Earnshaw, Gloucestershire Royal Hospital, discussed the role of the vascular specialist in such a programme. He highlighted that it would be necessary to provide a full range of treatment options and multi-disciplinary team and for all the results sent to a National Vascular Database. He also stated that there were challenges that lay ahead such as the formation of networks, quality assurance (screening/surgery) and finance.

UK SAT

Twelve-years follow-up from the UK SAT was presented for the UK Participants by Professor Janet Powell, Imperial College, London. On behalf of the Trial Participants, Powell commented, “Two randomised trials have shown no survival benefit associated with a policy of early open surgical repair compared to surveillance in patients with small abdominal aortic aneurysm (AAA). However, at eight years of follow-up there was a hint of an emerging survival benefit for early surgery.”

Trial protocol

As a result Powell and colleagues decided to perform a 12-year follow-up for mortality and aneurysm repair of the 1,090 patients enrolled in the UK SAT between 1991 and 1995 who presented with an abdominal aortic aneurysm measuring 4.0-5.5cm. Patients were then randomised to either early elective open repair or ultrasound surveillance until the aneurysm diameter exceeded 5.5cm, the aneurysm grew rapidly (more than 1cm per year) or there were symptoms referable to the aneurysm (eg, tenderness).

A total of 563 were randomised for early surgery intended to be performed within the first three months, with the remaining 527 patients allocated to the surveillance arm. Of the 563 in the surgical arm 520 were operated on (nine died before surgery, 21 were unfit, 13 refused, and 34 had no surgery for other reasons). In the surveillance arm, 321 underwent surgery and 283 were according to protocol.

The aneurysm became greater than 5.5cm in 190 patients, tender in 65 patients or grew by more than 1.0cm per year in 18 patients. A rupture of 1% per year was reported in the surveillance arm and 30-day mortality was 5.8%. The trial planners had anticipated a 2% 30-day mortality rate for elective surgery and 2% rupture rate in the surveillance arm, whereas a 1% rupture rate was actually found. This led the trialists to conclude that ‘surveillance is better than early surgery’. The 30-day costs showed a higher cost for early surgery £9,134 compared with £7,807 for surveillance.

12-year results

By the end of November 2005, a total of 714 patients (66%) had died, 929 (85%) had undergone aneurysm repair, 150 (14%) had died without aneurysm repair and 11 (1%) remained alive without aneurysm repair. After 12-years, mortality in the surgery and surveillance groups was 64% and 67%, respectively, unadjusted hazard ratio 0.90 (95% CI 0.77 to 1.04), p=0.139. Moreover, the policy of early surgery cost 17% more than a policy of delayed surgery following a period of surveillance, with a mean difference of £1,326 (95% CI 960 to 1,692). The death rate observed in small aneurysm patients was about twice that in the age-sex-matched population, differences being greater for women than men.

Therefore, the UK Participants concluded that there was no evidence for a late survival benefit with a policy of early surgery, although the majority of patients in the surveillance group (76%) eventually underwent aneurysm repair. “Despite this, a policy of early aneurysm repair still cost more than a policy surveillance for small aneurysms,” Powell added. “Surveillance remains the safe policy for managing asymptomatic AAA of <5.5cm diameter and all AAA patients should be targeted for cardiovascular risk reduction." Professor Roger Greenhalgh Principle Investigator of the trial said, “The 12-year findings underpin the basis of the intended UK national screening programme for AAA.” MASS trial

Also presented at the meeting was a mid-term estimate of mortality benefit and cost-effectiveness for AAA screening from MASS. Between 1997-1999, 67,770 men who were randomised to invitation to screening or not (no contact), was analysed at a mean of seven years follow-up (mean age 69). Benefits in terms of AAA-related and all-cause mortality were estimated alongside cost-effectiveness. Screening protocol included: <3.0cm not monitored; 3.0-4.4cm monitored annually; 4.5-5.4cm monitored every three months; and >5.5cm considered for elective surgery.

Seven-year follow-up

The relative risk reduction for AAA-related mortality in the group invited to screening was 47% (95% CI 325 to 58%). In terms of all-cause mortality, the observed risk reduction was 4% (95% CI 0% to 7%). The rupture rate in men initially screened normal has remained low at 0.54 ruptures per 10,000 person years (95% CI 0.25 to 1.02). Cost-effectiveness was estimated at £12,000 per life-year gained (95% CI £8,000 to £25,700) at seven years of follow-up based on AAA mortality and £4,900 per life-year gained. (95% CI infinite) based on all caused mortality. Costs were inflated to the 2004-5 financial year and discounted at 3.5% per annum. Life-years were adjusted for non-AAA mortality and were also discounted at 3.5% per annum.

Conclusions

The results from a large, pragmatic randomised trial show that the early mortality benefit is maintained in the mid-term and that the cost-effectiveness of screening becomes more favourable over time. At £12,500 per life-year gained, the cost-effectiveness of AAA screening in men is well below commonly accepted thresholds for interventions and compares favourably with other screening programmes already in place in the UK. invitation to screening or not (no contact), was analysed at a mean of seven years follow-up (mean age 69). Benefits in terms of AAA-related and all-cause mortality were estimated alongside cost-effectiveness. Screening protocol included: <3.0cm not monitored; 3.0-4.4cm monitored annually; 4.5-5.4cm monitored every three months; and >5.5cm considered for elective surgery

Date: Feb/2007

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