Ultrasound screening programs for abdominal aortic aneurysms (AAAs) that focus on a single round of screening for 65-year-old men will miss most acute AAAs, which occur in older men, according to a large prospective U.K. study published online in the Journal of the American Heart Association.
In a study that tracked acute AAAs over a 12-year period in Oxfordshire, U.K., a research team led by Dominic Howard, PhD, of the University of Oxford, found that two-thirds of aneurysms occurred in men and women 75 years of age or older. Extending AAA screening to also include scans of men and women at age 75, for example, would yield as much as a fourfold increase in prevented deaths, according to the group.
"The majority of acute events, related deaths, and life years lost now occur in those over age 75 and this will shift to age ≥ 85 over the next few decades," the authors wrote (JAHA, August 19, 2015). "These observations have implications for health service provision and national screening strategies."
Screening strategies
AAAs cause 1% of deaths in men older than age 65, and rupture is associated with an 80% mortality rate. Since elective surgical repair of screening-detected AAAs has a 30-day mortality rate of less than 6%, population screening has been considered to improve survival rates.
In the U.S., men age 65 who have smoked at least 100 cigarettes can receive Medicare AAA screening, while in the U.K., a national screening program has been implemented for men age 65. With recent evidence suggesting a decline in AAA rates among younger age groups and an increased incidence of rupture in older ages, the researchers sought to calculate the event rates, incidence, early case fatality, and long-term outcome of all acute aortic events taking place between 2002 and 2014 in Oxfordshire.
The researchers utilized population projections to predict acute AAA incidence rates over the next two decades and to estimate the likely impact of current and potential alternative screening programs, according to the group.
The researchers found 103 acute AAA events -- including 61 fatalities -- over the 12-year period in the study population of 92,728, representing an AAA incidence rate of 9 per 1,000,000. Nearly 73% of the acute AAA events were in males, and the mean age when aneurysms occurred was 78.7 years. The incidence rate increased with age.
| Acute AAA incidence rate by age range and gender | |||
| Age | Men | Women | Total |
| 55 to 64 years old | 5/100,000 | 2/100,000 | 7/100,000 |
| 65 to 74 years old | 23/100,000 | 5/100,000 | 28/100,000 |
| 75 to 84 years old | 28/100,000 | 10/100,000 | 38/100,000 |
| 85 years and older | 19/100,000 | 11/100,000 | 30/100,000 |
"In the first prospective, unselected, population-based study of acute AAA events, we have shown a high incidence and case fatality in older ages," the authors wrote.
Delving deeper into the data, the researchers found that only 22.3% of AAA incident events and 13.1% of aneurysm-related deaths occurred in men ages 65 to 74. Male smokers had the highest incidence rate (274 per 100,000 per year) for the age group of 65 to 74; 96.4% of AAA events in men younger than 75 occurred in those who had smoked at some point during their lives.
Low screening yield
After extrapolating their results to the overall U.K. population, the researchers concluded that the current U.K. AAA screening program would prevent only approximately 10.7% of AAA incident events, 5.6% of aneurysm-related deaths, and 12% of life years lost due to AAA.
An alternative strategy of screening men at age 65 and then all men again along with women at 75 would be much more effective, preventing approximately 28.1% of AAA incident events, 24.9% of aneurysm-related deaths, and 37.7% of life years lost. However, that protocol would more than double the number of screening ultrasound scans being performed (from 315,200 to 752,100).
The researchers noted, however, that by 2030, 91% of AAA deaths will be in men and women 75 or older. In addition, 61.6% of aneurysm-related deaths will take place in people age 85 and over, while 28.6% will be in women, according to the group.
Extending the current U.K. screening program to all men and women at age 75 would result in a three- to fourfold increase in the proportion of deaths prevented and life years lost, owing to the much higher incidence of acute AAA events at ages 75 to 84 than at ages 64 to 75 and the higher case fatality at older ages, the authors noted. "Although the uptake of screening might be lower at older ages and suitability for surgery of patients with screen-detected AAA might be lower than at age 65, we found no evidence that age alone should be a bar to screening," they wrote.
In fact, nearly all (97.4%) of patients 75 or older who had acute AAA were mobile before the event, but 86.8% were either dead or disabled afterward, according to the authors. What's more, the increase in 30-day case fatality of acute events with age was much greater in absolute terms than the increase in case fatality due to elective AAA repair. Also, one-quarter of the elective AAA repairs in the U.K. are already being performed in patients older than age 80, and the vast majority have excellent functional outcomes, they noted.
Another alternative screening strategy based on patient risk factors also could prevent more deaths and save more life years over the current model, while decreasing the number of scans required each year, according to the researchers.
"The U.S. Medicare screening program limits screening to men age 65 years who have ever smoked, whereas our data suggest that screening could be further limited to current smokers," the authors wrote. Screening only male current smokers at age 65, then all men at age 75 would result in an almost fourfold increase in the number of deaths prevented and a threefold increase in the number of life years saved, compared with the current U.K. strategy, with approximately a 20% reduction in the number of scans required.
