Conflicting European and North American Society Abdominal Aortic Aneurysm (AAA) Volume Guidelines Differentially Discriminate Peri-operative Mortality After Elective Open AAA Repair

Objective: The European Society for Vascular Surgery (ESVS) guidelines endorse a minimum abdominal aortic aneurysm (AAA) repair volume of 20 open (OAR) and or endovascular (EVAR) AAA repair procedures per year as a proxy for high quality care. In contrast, the Society for Vascular Surgery (SVS) espouses 10 exclusively OARs per year. Given the differences in these volume standards and definitions, debate persists regarding surgeon credentialing and healthcare resource allocation. This analysis aimed to determine which society endorsed volume benchmark better discriminates OAR mortality. Methods: A retrospective national registry based cohort analysis. Patients undergoing elective OAR were compared between centres meeting either ESVS (≥ 20 AAA procedures/year) or SVS (≥ 10 OARs/year) volume thresholds within the Vascular Quality Initiative (2010 – 2020). The primary outcome was in hospital death. Logistic regression was used for risk adjusted comparisons. Results: A total of 8 761 OARs were performed at 193 US centres, and the median (IQR) volume was 6.6 (3.3, 9.9) OARs/year. When applying the SVS centre volume definition, the proportion of centres meeting ESVS and SVS minimum case thresholds was 12% (n = 22) and 25% (n = 48), respectively. The absolute mortality difference was 0.3% between centres performing ≥ 20 vs. ≥ 10 OARs/year (2.6% vs. 2.9%; p = .51). There was an incremental association between OAR volume and crude mortality rate; however, this absolute difference between lower and higher thresholds was only 0.2%/procedure (OR 0.98, 95% CI 0.97 – 0.99; p < .001). Moreover, no difference in risk adjusted mortality was detected between volume standards (≥ 10 vs. ≥ 20; p = .78). In sub-analysis, the ESVS ≥ 20 total composite AAA repair volume threshold was not associated with mortality (p = .17); however, increasing the proportion of OAR cases making up the total annual AAA centre volume inversely correlated with mortality (p = .008). Conclusion: It appears that the SVS endorsed AAA centre volume threshold using exclusively OAR had a modest ability to discriminate peri-operative mortality outcomes and was superior to the current composite ESVS volume guideline in differentiating centre performance. These findings raise questions regarding the clinical validity of using EVAR as a volume proxy for OAR.