By Eleanor McDermid, Senior medwireNews Reporter
The interval between ultrasound surveillance scans of small abdominal aortic aneurysms (AAAs) could be substantially increased from current recommendations, suggest meta-analysis findings.
"We have demonstrated that most of the smallest AAAs remain quiescent over many years," say study author Simon Thompson (University of Cambridge, UK) and colleagues.
The team found that it took 7.4 years for men with an AAA of 3 cm in diameter to accumulate a 10% chance of their AAA reaching a diameter of 5.5 cm (the usual threshold for surgical intervention). The corresponding times for men with AAAs of 4 and 5 cm were 3.2 and 0.7 years, respectively.
"The current findings have implications for AAA surveillance programs worldwide," say Thompson et al. "Because screening for AAA is becoming established in many countries, there will soon be large numbers of individuals under surveillance for AAA with the large majority having aneurysm diameters between 3.0 and 4.5 cm."
Their findings suggest that screening intervals could be considerably longer than currently recommended, they say.
Overall, the average growth rate of a 3 cm AAA in men was 1.28 mm per year, and that of a 5 cm AAA was 3.61 mm per year. Each 0.5 cm increase in baseline AAA diameter was associated with a 0.59 mm increase in annual growth rate. However, there was a large 95% confidence interval of 0.51-0.66 mm due to substantial heterogeneity between the studies, which, the researchers say, is unexplained.
Rupture was rare, occurring in 178 of the 11,262 men from the 18 studies in the meta-analysis, and in 50 of the 1314 women. Among men, rupture rates almost doubled with each 0.5 cm increase in baseline AAA diameter.
There were some notable differences between men and women, the team reports in JAMA. Although both genders took a similar time for their AAAs to grow to a size that required intervention, the rupture rate was considerably higher in women than men, irrespective of baseline diameter. For example, it was 2.2 versus 0.5 per 1000 person-years for a baseline diameter of 3 cm and 29.7 versus 6.4 per 1000 person-years for a baseline diameter of 5 cm.
Likewise, the time to reach a 1% chance of rupture was 3.5 versus 8.5 years in women and men, respectively, with a 3 cm AAA, and 0.7 versus 1.4 years in those with a 5 cm AAA.
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