The influence of study design on the evaluation of ruptured abdominal aortic aneurysm treatment

The best strategy in the treatment for ruptured abdominal aortic aneurysm (RAAA) is an ongoing matter of debate. Differently from several retrospective studies, recent randomized controlled trials (RCTs) failed to demonstrate the superiority of endovascular repair (EVAR) over open repair (OPEN). The aim of the present study was to compare 30-day mortality of EVAR and OPEN in RAAA according to different study designs through a systematic review and meta-analysis.

A systematic literature search of all series comparing the outcome of EVAR and OPEN in RAAA was performed. Studies on symptomatic aneurysms without frank ruptures were excluded. The analyses evaluated the effect of the study design on EVAR versus OPEN 30-day mortality. The pooled mortality risk was expressed as odds ratio (OR) with a 95% confidence interval (CI) by random effect model.

Four different study designs were evaluated. 1) Patients allocation in EVAR or OPEN was "unbiased" (3 studies, 2 RCTs): there was no superiority treatment in EVAR versus OPEN (OR, 1.58; 95% CI, 0.82-3.06; P = 0.17). 2) Patients submitted to EVAR were compared with a historical OPEN group (2 studies): no difference between EVAR and OPEN (OR, 3.55; 95% CI, 0.47-26.62; P = 0.22). 3) EVAR was the preferential treatment and OPEN was confined to patients with unsuitable anatomy for endovascular procedures (18 studies): in this type of study OPEN had a higher risk of 30-day mortality (OR, 2.18; 95% CI, 1.61-2.96; P < 0.00001). 4) The 30-day mortality after EVAR introduction in centers using both EVAR and OPEN was compared with the only OPEN treatment (7 studies): the latter had higher mortality compared with the protocol with both EVAR and OPEN options (OR, 2.26; 95% CI, 1.41-3.63; P = 0.0007).

Only few studies are available to compare EVAR and OPEN in an "unbiased" cohort, with no significant differences between the 2 treatments. However, after the introduction of EVAR and OPEN protocols, the overall mortality for RAAA was reduced compared with the only OPEN option, suggesting a beneficial effect of EVAR in selected cases.