Background: There is a large body of evidence documenting better outcomes for abdominal aortic aneurysm (AAA) repairs performed in high-volume centers. However, it remains unknown if the strength of this volume–outcome relationship is moderated by race or socioeconomic status (SES). Methods: This is a cross-sectional retrospective cohort study evaluating 60,618 Medicare fee-for-service beneficiaries undergoing open AAA repair across 1,649 hospitals between 2005 and 2009. We selected, a priori, black race and low SES as vulnerable populations based on previous reports showing each is independently associated with higher mortality. Next, we divided hospitals into quintiles of procedural volume and used logistic regression to compare risk-adjusted rates of inpatient mortality across volume quintiles for the overall study population and separately by race (black versus nonblack) and SES (low, middle, and high). Results: Overall, patients treated in the lowest-volume hospitals (LVHs) had higher risk-adjusted inpatient mortality rates than patients treated in the highest-volume hospitals (HVHs) (15.3% vs. 10.6%, P < 0.001). Higher mortality was associated with black versus nonblack race (12.9% vs. 11.7%, P < 0.001) and low SES versus high SES (12.2% vs. 11.6% P < 0.001). While nonblack patients treated in LVHs had higher odds of mortality (versus HVHs, adjusted odds ratio (aOR) 1.83 [1.59–2.11]), this volume–outcome effect was greater for black patients (aOR 2.60 [1.63–4.16]). In contrast, high and low SES patients experienced similar differences in mortality when treated in LVHs (aOR 1.79 [1.49–2.12]; aOR 1.72 [1.28–2.30], respectively). Conclusions: While a volume–outcome effect was observed in all patients, black patients appeared to derive a disproportionate benefit from undergoing open AAA repair in HVHs. The mechanism underlying these disparate outcomes remains unclear but warrants further evaluation of contributing hospital and patient factors.
