In contrast to previous studies, screening for abdominal aortic aneurysms in older men does not appear to have a significant effect on overall mortality, according to a prospective, randomized study.
Mortality from ruptured AAA remains high in older men, which has prompted four previous large randomized trials to explore whether screening men aged 65 years and older might reduce mortality.
Writing in the October 31 online edition of JAMA Internal Medicine, the authors reported the long-term outcomes of an Australian population-based trial of screening for abdominal aortic aneurysms in 49,801 men aged 64-83 years, of whom 19 249 were invited to screening and 12,203 of those underwent screening (isrctn.org Identifier: ISRCTN16171472).
After a mean 12.8 years of follow-up, there was a non-significant 9% lower mortality in the invited screening group compared to the control group and a non-significant 8% lower mortality among men aged 65-74 years.
Overall, there were 90 deaths from ruptured AAA in the screening group and 98 in the control group (JAMA Internal Medicine 2016, October 31. DOI:10.1001/jamainternmed.2016.6633).
The prevalence of abdominal aortic aneurysms with a diameter at or above 30 mm was 6.6% in men aged 65-74, and 0.4% for those with a diameter of 55 mm or above.
While the rate of ruptured abdominal aortic aneurysms was significantly lower in the invited group compared to the control group (72 vs. 99, P = .04), the 30-day mortality after surgery for rupture was higher in the invited group compared to the control group (61.5% vs. 43.2%).
Screening had no meaningful impact on the risk of all-cause, cardiovascular, and other mortality, but men who had smoked had a higher risk of rupture and of death from a rupture than those who had never smoked, regardless of screening status.
The rate of total elective operations was significantly higher in the invited group compared to controls (536 vs. 414, P < .001), mainly in the first year after screening.
The authors calculated that to prevent one death from a ruptured abdominal aortic aneurysm in five years, 4784 men aged 64-83 years or 3290 men aged 65-74 years would need to be invited for screening.
While the strength of the study was that it was truly population-based – using the electoral roll – the authors said the lack of a benefit from screening was likely due to the relatively low rate of rupture and death from AAA, as well as a high rate of elective surgery for this condition, in the control group.
The non-significant 8% reduction in mortality observed in the study was significantly less than the 42% and 66% reductions seen in previous trials with a similar length of follow-up.
The authors suggested this may also have been related to a lower fraction of invited men participating in screening, but pointed out that the incidence of AAA in men is declining.
“The reason for the decrease in incidence and prevalence is multifactorial but is probably driven by differences in rates of smoking and cessation because the relative risk for AAA events is 3- to 6-fold higher in smokers compared with non-smokers,” they wrote.
The authors said selective screening of smokers or ex-smokers may be more effective, but pointed out that this approach would miss around one-quarter of aneurysms. However they suggested more targeted screening may yet achieve a benefit.
“The small overall benefit of population-wide screening does not mean that finding AAAs in suitable older men is not worthwhile because deaths from AAAs in men who actually attended for screening were halved by early detection and successful treatment.”
The study was supported by the National Health and Medical Research Council Project. The authors reported that they had no conflicts of interest.