Surveillance Intervals for Small Abdominal Aortic Aneurysms: A Meta-Analysis
How often is surveillance ultrasound imaging clinically useful in patients with abdominal aortic aneurysms (AAAs)?
Patient-level data from studies evaluating AAA growth and rupture with serial ultrasound imaging were examined to identify rates of growth to 5.5 cm or rupture. A total of 18 data sets with 15,471 patients were examined. Inclusion criteria included randomized trials or observational studies of consecutive patients, and patients with AAA diameters of 3.0-5.4 cm at baseline. Growth rates and risk of rupture were evaluated based on size, gender, and other risk factors.
Mean growth rate was related to gender and baseline diameter, and ranged from 1.3 mm/year for men (1.5 mm/year in women) with a 3.0 cm aorta, to a mean rate of 3.6 mm/year for both men and women with a 5.0 cm AAA. The time to have a 10% chance to achieve the surgical threshold of 5.5 cm ranged from 7.4 years for men (6.9 years in women) for a 3.0 cm aorta, to 0.7 years (in both genders) for a 5.0 cm aorta. For each 0.5 cm increase in diameter, growth rates increased a mean of 0.6 mm/year, and rupture rates increased by a factor of 1.9. The mean time to have a 1% chance of rupture for a 3.0 cm aorta was 8.5 years for men and 3.5 years for women, and this time decreased in the presence of a 5.0 cm aorta to 1.4 years for men and 0.7 years for women.
The authors concluded that there are marked differences in the rate of growth and risk of rupture between individuals with smaller versus larger AAAs. Serial imaging may be needed less frequently in many patients with smaller AAAs.
This study has important implications in how we perform serial screening of patients with AAAs. As current guidelines have significant variability in their recommendations for serial imaging intervals, these data may improve our ability to develop more uniform and cost-effective guidelines that suggest imaging intervals based on diameter- and gender-based risk. Another important finding was that the risk of rupture was comparable between men with a 5.5 cm aorta and women with a 4.5 cm aorta, suggesting a need for more research to identify the appropriate treatment of women with an AAA in the 4.5-5.4 cm range.
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