Deaths from abdominal aortic aneurysm among Swedish men are going down – but not because they’re being screened for the potentially fatal condition.
Although the death rate has decreased by 70% since the early 2000s, screening only saved 2 lives per 10,000 men screened. It did, however, increase by 59% the risk of unnecessary surgery,
“Screening had only a minor effect on AAA mortality,” wrote Dr. Johansson of the University of Gothenburg (Sweden). “In absolute numbers, only 7% of the benefit estimated in the largest trial of AAA screening was observed. The observed large reductions in AAA mortality were present in both the screened and nonscreened cohorts and were thus mainly caused by other factors – probably reduced smoking. … Our results call the continued justification of AAA screening into question.”
In Sweden, all men aged 65 years are invited to a one-time ultrasound abdominal aorta screening. Most participate. Anyone with an aneurysm is followed up at a vascular surgery clinic, with surgery considered if the aortic diameter is 55 mm or larger.
Dr. Johansson and her colleagues plumbed national health records to estimate the risks and benefits of this routine screening. The study comprised 25,265 men invited to join the AAA screening program in Sweden from 2006 to 2009. Mortality data were compared with those from a contemporaneous cohort of 106,087 men of similar age who were not invited to screen. Finally, the mortality data were compared with national trends in AAA mortality in all Swedish men aged 40-99 years from 1987 to 2015.
A multivariate analysis adjusted for cohort year, marital status, educational level, income, and whether the patient already had an AAA diagnosis at baseline.
From the early 2000s to 2015, AAA mortality among men aged 65-74 years declined from 36 to10 deaths per 100,000. This 70% reduction was similar in both screened and unscreened populations; in fact, the decline began about a decade before population-based screening was introduced and continued to decrease at a steady rate afterward.
After 6 years of screening, there was a 30% reduction of AAA mortality in the screened population, compared with the unscreened, translating to an absolute mortality reduction of two deaths per 10,000 men offered screening.
Screening increased by 52% the number of AAAs detected. The absolute difference in incidence after 6 years of screening translated to an additional 49 overdiagnoses per 10,000 screened men.
Looking back into the mid-1990s, the investigators saw the numbers of elective AAA surgeries rise steadily. In the adjusted model, screened men were 59% more likely to have this procedure than unscreened. The increased risk didn’t come with an equally increased benefit, though. There was a 10% decrease in AAA ruptures, “rendering a risk of overtreatment of 19%, or 19 potentially avoidable elective surgeries per 10,000 men,” the team noted. “Sixty-three percent of all additional elective surgeries for AAA might therefore have constituted overtreat.”
The findings are at odds with large published studies that found a consistent benefit to screening.
“Compared with results at 7-year follow-up of the largest trial of screening for abdominal aortic aneurysm [ ], we found about half of the benefit in terms of a relative effect and 7% of the estimated benefit in terms of absolute numbers [2 vs. 27 avoided deaths from AAA per 10,000 invited men]. Compared with previous estimates of overdiagnosis and overtreatment, we found a lower absolute number of over-diagnosed cases [49 vs.176 per 10,000 invited men] and fewer overtreated cases [19 vs. 37 per 10,000 invited men]. However, since the harms of screening decreased less than the benefit, the balance between benefits and harms seems much less appealing in today’s setting.”
None of the authors had any financial disclosures.
The study by Johansson et al. indicates a significant risk of overdiagnosis associated with routine screening for abdominal aortic aneurysm: Those risks may not be as clinically harmful as might be assumed, Stefan Acosta, MD, wrote in an accompanying editorial (Lancet 2018; 391: 2394-95).
“Although I agree that having a small AAA that needs long-term follow-up might be associated with negative psychological consequences, there could also be a window of opportunity [eg. with statins, antiplatelet therapy, and blood pressure reduction], for individuals with increased burden of cardiovascular disease. Indeed, screening for AAA, peripheral artery disease, and hypertension, with the initiation of relevant pharmacotherapy, if positive, reduces all-cause mortality and some evidence suggests that this approach of multifaceted vascular screening instead of isolated AAA screening should be considered.”
When performed according to the established criteria for elective AAA surgery, the procedure is associated with less than 1% postoperative mortality, “mainly because of wide implementation of endovascular aneurysm repair, a minimally invasive method.”
The 6-year follow-up time, as the authors noted, is relatively short. A 2016 review of the Swedish Nationwide Abdominal Aortic Aneurysm Screening Program determined that significant mortality benefit could take 10 years to materialize( ).
The full impact of Sweden’s remarkable decrease in smoking is almost certainly making itself known in these outcomes – smoking is implicated in 75% of AAA cases.
“The decreased prevalence of smoking in Sweden, from 44% of the population in 1970 to 15% in 2010, should be viewed as the main cause of the decreasing incidence and mortality of AAA. Every percent drop in the prevalence of smoking will have a huge effect on smoking-related diseases, such as cancer and AAA.”
Dr. Stefan is a vascular disease researcher at Lund (Sweden) University. He had no financial disclosures.