In contrast to the commonly adopted surveillance intervals in current abdominal aortic aneurysm screening programmes, surveillance intervals of several years may be clinically acceptable for the majority of patients with small aneurysms, as the smallest aneurysms often do not appear to change significantly over many years, according to a meta-analysis of previous studies reported in the 27 February issue of the Journal of the American Medical Association (JAMA).
“The survival rate following rupture of an abdominal aortic aneurysm is only 20%, making aneurysms an important cause of mortality,” according to background information in the article. “In patients with small aneurysms (diameter <5.5cm), the risk of rupture is lower than the risk of surgery and surveillance is indicated. The majority of small aneurysms grow slowly, but there is substantial variation in growth rates between different individuals. The intervals between ultrasound surveillance examinations used in randomised trials of screening depend on aneurysm size. However, no consensus exists regarding the optimal time intervals between ultrasounds.”
To better guide abdominal aortic aneurysm surveillance efforts, Simon G Thompson, University of Cambridge, UK, and colleagues including the Vascular Surgery Research Group, Imperial College London, UK, conducted a study to determine the rates at which small aneurysms progress to reach the surgery threshold diameter of 5.5cm and the risk of rupture over time. Via a meta-analysis, the authors assessed individual patient data from studies of small aneurysm growth and rupture. A total of 18 studies containing records from 15,471 individual patients (13,728 men and 1,743 women) under surveillance for small aneurysms were included in the analysis. Most studies used 5.5cm as the threshold for surgical intervention, used only ultrasound scans, and recorded external aortic diameters.
The RESCAN study researchers found that aneurysm growth and rupture rates varied considerably across studies. Each 0.5cm increase in baseline aneurysm diameter resulted in a 0.59mm per year increase in average aortic growth rate. Rupture rates in men increased by a factor of 1.9 for every 0.5cm increase in baseline aneurysm diameter. For men with a 3cm aneurysm, the estimated average time taken to have a 10% chance of reaching the surgery threshold diameter 5.5cm was 7.4 years. The corresponding average times for 4cm and 5cm aneurysms were 3.2 years and eight months, respectively.
To control the risk of rupture in men to below 1%, the corresponding estimated surveillance intervals are 8.5 years for a 3cm and 17 months for a 5cm aneurysm.
While absolute growth rates were similar for women and men (particularly for larger baseline aneurysm diameters), there were marked differences in the absolute risks of rupture. Women had a four-fold greater rupture risk for all aneurysm sizes and reached a rupture risk of greater than 1% in a much shorter time than men.
“Current recommendations for surveillance intervals vary widely although the intervals usually decrease with increasing aneurysm diameter (for example, one year for aneurysm measuring 3–4.4cm and three months for those measuring 4.5–5.4cm in the current screening programme in England),” the authors wrote. The findings of this study indicate that for men “these surveillance intervals could be extended to three years for aneurysms measuring 3–3.9cm, two years for 4–4.4cm, and yearly for 4.5–5.4cm; the risk of rupture would be maintained at less than 1%. For a US patient with a 3cm aneurysm detected by screening, this would reduce the average number of surveillance scans from approximately 15 to seven.”
“There is a need for more research regarding women with aneurysms in the diameter range of 4.5 to 5.4cm. Since national rates of aneurysm rupture are declining, recommended surveillance intervals may need to be reassessed.
There is also a need to establish the cost effectiveness of different surveillance policies. Decreasing surveillance frequency would reduce surveillance costs. However, it may also slightly increase rupture rates and increase patient anxiety. This would decrease overall life expectancy and quality of life in abdominal aortic aneurysm patients under surveillance and increase costs attributable to emergency surgery,” the researchers concluded.
CX35 topics on aneurysm screening
- Optimising an abdominal aortic aneurysm screening programme – Jonothan Earnshaw
- Smoking habits among patients with screening detected abdominal aortic aneurysms – Anders Wanhainen
- Doxycycline and aortic aneurysm growth – Jan Lindeman
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