Is it time to reconsider abdominal aortic aneurysm screening programmes?
CX 34 delegates on Sunday heard a variety of reasons why it might be time to question the very foundations on which national aneurysm screening programmes are based. With a population that lives longer, smokes less and has lower cholesterol levels than in the past, it seems that people are developing abdominal aortic aneurysms later in life. Do we need to raise the age threshold for screening? With all trial evidence so far having studied abdominal aortic aneurysm in men between the ages of 65 and 74, is a policy selecting 65 as the age for screening still valid? Have cardiovascular risk prevention programmes pre-empted national aneurysm screening programmes? What is an optimum rescanning interval?
Roger Greenhalgh, London, UK, addressed Alan Scott, Plymouth, UK, as they were both instrumental in providing the evidence on the 5.5cm threshold and basis of screening and said, “We made certain decisions at the time about thresholds and about screening based on information we had at the time. We are hearing a story emerging and may have to be very flexible, and re-look at thresholds and screening intervals and find that they may not be fixed intervals. They might be sliding scale intervals,” he said.
Scott replied that at the time they had been careful to set up the rescreening intervals so that they were safe, erring perhaps on the side of caution.
National screening programmes in the UK, Sweden and Australia are observing a recent reduction in growth and rupture of abdominal aortic aneurysms in 65-year-olds. Jonothan Earnshaw, Gloucester, UK, who opened the session on Sunday at CX34, took to the podium to speak about the UK’s national abdominal aortic screening programme.
In a CX exclusive, he shared draft data showing that between 2009–2012 the programme (with 40% coverage) had screened 157,730 men. The uptake was 80.17% and 2,494 (1.57%) abdominal aortic aneurysms larger than 3cm were detected. Four hundred and four men were referred for surgery.
“Perhaps the most interesting point is we were expecting, based on data from the MASS trial, to find approximately 4% of 65-year-olds with aneurysms. In fact, we have only found 1.57%. That is still a significant number of men – we have now referred over 400 men for vascular opinion.
I cannot give you outcome data, but of the first 130 screen-detected, 129 patients had survived the intervention.” Earnshaw told delegates that the main issue in screening in 2012 was the fact that “We are not finding as many aneurysms as we thought we would. Twenty-year data from the Gloucester programme showed that the mean aortic diameter has reduced from 21mm in 1991 to 17mm in 2009. There is something happening to the 65-year-old male aorta in Gloucester. This reduction in the number of aneurysms is mirrored elsewhere, in Scandanavia and Australasia, and does seem to be real. Aneurysms do seem to be going away, which is ironic, when we are starting a screening programme.”
On the issue of cost-effectiveness, Earnshaw told delegates that ongoing research suggested that that it was likely that aneurysm screening at the current prevalence would remain cost-effective.
Anders Wanhainen, Uppsala, Sweden, who then took the stage shared similar observations about the reduction of aneursysms being observed. He told delegates that Sweden had adopted a commonly suggested screening design with a single ultrasound examination of men at the age of 65. “The national abdominal aortic screening programme has a nearly nationwide coverage today,” he said. Wanhainen said that the prevalence of abdominal aortic aneurysms in the target population was lower than expected indicating a change in the epidemiology of the disease, mainly attributed to a noticeable reduction in smoking frequency. “We therefore need to continue to monitor and assess the screening programmes already established and simultaneously evaluate alternative screening strategies,” he said.
Describing the situation in Australia, Paul Norman, Fremantle, said that experts were adopting a wait and watch approach rather than implementing a national screening programme because the magnitude of benefit from screening is small. “Mortality is falling without screening. I would question whether there is enough of a public health problem to warrant screening.”
Is the rupture rate falling?
Janet Powell, London,UK, told delegates that the rate and volume of aneurysm rupture is declining. She made the point that smoking prevalence had decreased, and use of lipid-lowering and antihypertensive drugs had increased in those who were 65+ years. “The small aneurysm rupture rate is decreasing and deaths from (and hospital admissions for) large ruptured aneurysm are decreasing. Since selection for repair and its mortality are unchanged, have cardiovascular risk prevention programmes pre-empted national aneurysm screening programmes?” she asked.
Martin Bjorck, Uppsala, Sweden, told delegates that an aneurysm screening programme should include a smoking cessation programme, promotion of exercise and healthy diet and statin treatment prior to surgery. There should also be hypertension treatment, according to standard of care, he said. “As we all know, screening elderly men for abdominal aortic aneurysm, and repair of those who have or later develop large aneurysms, reduce aneurysm mortality by between 50 and 70%. “Can we prevent growth of small aneurysms? Can we prevent cardiovascular events? Can we prolong life with secondary prevention? Unfortunately, we lack specific data on patients with screening detected aneurysms,” he said. “Data on the possible effects of statins on aneurysm growth rates are contradictory, and there is no evidence to support that growth is decreased. What is shown, however, in randomised trials, is that short-term statin treatment reduces perioperative cardiac events and mortality, by approximately 50%. Long-term statin treatment prevents events among patients with cardiovascular disease, but there are no specific data on abdominal aortic aneurysm patients.”
Simon Thompson, Cambridge, UK, speaking on behalf of the RESCAN collaboration, told delegates that surveillance intervals for small abdominal aortic aneurysms differed between surveillance programmes. “Some are based on screening trials, but there is no good evidence base/direct comparative data.” The RESCAN Collaboration analysed small aneurysms measuring 3–5.4cm which came from individual patient data over time collated from surveillance programmes/other longitudinal studies.
Data were collated from 18 studies in the UK, Europe, North America, and Australia, involving 15,471 patients followed for up to eight years. There were 228 ruptures, aneurysms were measured mainly by ultrasound (external diameters) and there was a 5.5cm threshold for surgery. Results of the analysis showed that the average growth rate is 2.2mm/year and the average rupture rate is 0.2% per year. “For each 0.5cm increase in aneurysm diameter, the growth rate goes up by 0.5mm/year and the rupture rate doubles. There is large heterogeneity in these rates between studies, which is unexplained. Women have the same growth rates but four times the rupture rates of men, at each abdominal aortic aneurysm diameter.” Thomson told delegates that the clinically acceptable surveillance intervals for men are several years for 3–4cm aneursyms and six months for 5cm aneurysms. “Intervals/threshold for surgery in women should reflect those for men with 0.5–1cm larger aneurysms, and the cost-effectiveness of different surveillance policies needs to be formally assessed,” he said.