Background: An abdominal aortic aneurysm (AAA) is an abnormal ballooning of the major abdominal artery. Some AAAs present as emergencies and require surgery; others remain asymptomatic. Treatment of asymptomatic AAAs depends on many factors, including size: risk of rupture increases with aneurysm size. Large asymptomatic AAAs (> 5.5 cm in diameter) are usually operated on; very small AAAs (< 4.0 cm diameter) are monitored with ultrasonography. The optimal timing of surgery would benefit from further evidence.
Objectives: This review compared long-term survival in patients with AAAs of diameter 4.0 to 5.5 cm who received immediate surgical repair versus routine ultrasound surveillance.
Search strategy: Trials were identified through searching the Cochrane Peripheral Vascular Diseases Group Specialised Register and reference lists of relevant articles, supplemented by handsearches of recent conference proceedings and information from experts in the field.
Selection criteria: Randomised controlled trials in which men and women with asymptomatic AAAs of diameter 4.0 to 5.5 cm were randomly allocated to immediate surgery or imaging-based surveillance at least every 12 months. Outcomes had to include mortality or survival.
Data collection and analysis: One author (GF) abstracted the data which were cross-checked by the other authors (DJB, FGRF, JTP). Due to the small number of trials, formal tests of heterogeneity and sensitivity analyses were not conducted.
Main results: Two trials, the UK Small Aneurysm Trial (UKSAT) and the Aneurysm Detection and Management (ADAM) trial, fulfilled the inclusion criteria. Both showed an early survival benefit in the surveillance group (due to 30-day operative mortality with surgery) but no significant differences in long-term survival (adjusted hazard ratio (HR) 0.88, 95% confidence interval (CI) 0.75 to 1.02, mean follow up 10 years) (UKSAT); HR 1.21, 95% CI 0.95 to 1.54, mean follow up 4.9 years) (ADAM). The meta-analysis of mortality at six years revealed a non-significant association (Peto odds ratio 1.11, 95% CI 0.91 to 1.34). Neither trial independently had sufficient power for subgroup analyses (for example, by age or aneurysm size).
Authors' conclusions: The results from the two trials to date suggest no overall advantage to early surgery for small AAA (4.0 to 5.5 cm) but provide no additional guidelines for 'best-care' management of subgroups of patients. An individual patient-level data meta-analysis using the combined data from these studies will have sufficient power to conduct subgroup analyses, which are expected to elucidate risks and benefits of each treatment option for subgroups based on age, fitness and aneurysm size.