Systematic review and meta-analysis of growth rates of small abdominal aortic aneurysms

Background: Small abdominal aortic aneurysms are usually asymptomatic and managed safely in ultrasound surveillance programmes until they grow to a diameter threshold where intervention is considered. The aim of this study was to synthesize systematically the published data on growth rates for small aneurysms to investigate the evidence basis for surveillance intervals. Methods: This was a systematic review of the literature published before January 2010, which identified 61 potentially eligible reports. Detailed review yielded 15 studies providing growth rates for aneurysms 3.0-5.5 cm in diameter (14 in millimetres per year, 1 as percentage change per year). These studies included 7630 people (predominantly men) enrolled during 1976-2005. Results: The pooled mean growth rate was 2.32 (95 per cent confidence interval 1.95 to 2.70) mm/year but there was very high heterogeneity between studies; the growth rate ranged from -0.33 to +3.95 mm/year. Six studies reported growth rates by 5-mm diameter bands, which showed the trend for growth rate to increase with aneurysm diameter. Simple methods to determine growth rate were associated with higher estimates. Meta-regression analysis showed that a 10-mm increase in aneurysm diameter was associated with a mean(s.e.m.) 1.62(0.20) mm/year increase in growth rate. Neither mean age nor percentage of women in each study had a significant effect. On average, a 3.5-cm aneurysm would take 6.2 years to reach 5.5 cm, whereas a 4.5-cm aneurysm would take only 2.3 years. Conclusion: There was considerable variation in the reported growth rates of small aneurysms beyond that explained by aneurysm diameter. Fuller evidence on which to base surveillance intervals for patients in screening programmes requires a meta-analysis based on individual patient data.