Systematic Review and Meta-Analysis of the Incidence of Rupture, Repair, and Death of Small and Large Abdominal Aortic Aneurysms under Surveillance

Abstract

Background: The ultimate goal of treating patients with abdominal aortic aneurysms (AAAs) is to repair them when the risk of rupture exceeds the risk of repair. Small AAAs demonstrate a low rupture risk, and recently, large AAAs just above the threshold (5.5-6.0 cm) seem to be at low risk of rupture as well. The present review aims to investigate the outcomes of AAAs under surveillance through a comprehensive systematic review and meta-analysis.

Methods: PubMed, Embase, and the Cochrane Central Register were searched (22 March 2022; PROSPERO; #CRD42022316094). The Cochrane and PRISMA statements were respected. Blinded systematic screening of the literature, data extraction, and quality assessment were performed by two authors. Conflicts were resolved by a third author. The meta-analysis of prevalence provided estimated proportions, 95% confidence intervals, and measures of heterogeneity (I²). Based on I², the heterogeneity might be negligible (0-40%), moderate (30-60%), substantial (50-90%), and considerable (75-100%). The primary outcome was the incidence of AAA rupture. Secondary outcomes included the rate of small AAAs reaching the threshold for repair, aortic-related mortality, and all-cause mortality.

Results: Fourteen publications (25,040 patients) were included in the analysis. The outcome rates of the small AAA group (<55 mm) were 0.3% (95% CI 0.0-1.0; I² = 76.4%) of rupture, 0.6% (95% CI 0.0-1.9; I² = 87.2%) of aortic-related mortality, and 9.6% (95% CI 2.2-21.1; I² = 99.0%) of all-cause mortality. During surveillance, 21.4% (95% CI 9.0-37.2; I² = 99.0%) of the initially small AAAs reached the threshold for repair. The outcome rates of the large AAA group (>55 mm) were 25.7% (95% CI 18.0-34.3; I² = 72.0%) of rupture, 22.1% (95% CI 16.5-28.3; I² = 25.0%) of aortic-related mortality, and 61.8% (95% CI 47.0-75.6; I² = 89.1%) of all-cause mortality. The sensitivity analysis demonstrated a higher rupture rate in studies including <662 subjects, patients with a mean age > 72 years, >17% of female patients, and >44% of current smokers.

Conclusion: The rarity of rupture and aortic-related mortality in small AAAs supports the current conservative management of small AAAs. Surveillance seems indicated, as one-fifth reached the threshold for repair. Large aneurysms had a high incidence of rupture and aortic-related mortality. However, these data seem biased by the sparse and heterogeneous literature overrepresented by patients unfit for surgery. Specific rupture risk stratified by age, gender, and fit-for-surgery patients with large AAAs needs to be further investigated.

Keywords: aneurysm; aortic aneurysm; aortic disease; aortic pathology; mortality; ruptured aneurysm.

Figure 1

PRISMA flow diagram.

Figure 2

Small abdominal aortic aneurysm pooled estimate of rupture incidence. The vertical dotted line represents the mean proportion of all studies. The black horizontal lines represents the confidence interval of each single study [6,14,23,24,26,29,32].

Figure 3

Funnel plot and Egger’s test of small abdominal aortic aneurysm pooled estimate of rupture incidence.

Figure 4

Sensitivity analysis of small abdominal aortic aneurysm pooled estimate rupture (A) by sample size (< vs. >662 patients), (B) by mean age (< vs. >72 years old), (C) by female proportion (< vs. >17%), and (D) by current smoker proportion (< vs. >44%). The vertical dotted line represents the mean proportion of all studies. The black horizontal lines represents the confidence interval of each single study [6,14,23,24,26,29,32].