Surgery for small asymptomatic abdominal aortic aneurysms
Abstract
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 methods
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.
PICOs
Plain language summary
Surgery for small abdominal aortic aneurysms that do not cause symptoms
An aneurysm is a ballooning of an artery (blood vessel), which can happen in the major artery in the abdomen (aorta). The cause is unknown. Ruptured aneurysms cause death unless surgical repair is rapid, which is difficult to achieve. Surgery for patients with aneurysms more than 5.5 cm in diameter or who have associated pain is considered necessary to relieve symptoms and to reduce the risk of rupture and death, although there are risks with surgery. Surgical repair of the aneurysm consists of insertion of a prosthetic inlay graft either by open surgery or by endovascular repair. Small abdominal aortic aneurysms without symptoms are at low risk of rupture. They are monitored through regular imaging so that they can be surgical repaired when they subsequently become bigger.
This review identified two well‐conducted, controlled trials that randomised 2026 patients with small (diameter 4.0 to 5.5 cm) asymptomatic aneurysms in the abdominal aorta to have immediate standard open repair surgery or routine ultrasound surveillance every six months. The trials did not show a meaningful difference in long‐term survival between the two treatment options. The results indicate that there was no long‐term survival advantage with immediate surgery compared to selective surveillance over 3.5 to 10 years follow up. Both trials showed an early survival benefit in the surveillance group because of the 30‐day operative mortality with surgery. Trial participants assigned to selective surveillance were followed and surgery was performed if the aneurysm was enlarging, reached 5.5 cm in diameter, or became symptomatic. Some 62% to 75% of these participants eventually had surgical repair of the aneurysm. Neither of the identified trials enrolled a large enough number of patients to investigate possible survival differences between the treatment options for people of different age or with different sized aneurysms. There was insufficient detail to combine the published data from the two trials without having individual patient‐level data.
