Racial Disparity in the Relationship Between Hospital Volume and Mortality Among Patients Undergoing Coronary Artery Bypass Grafting

Objective: To examine whether the volume-mortality relationship in coronary artery bypass grafting (CABG) differs by race and operative risk. Summary Background Data: In-hospital mortality after CABG is inversely associated with hospital volume. Racial disparities exist in the outcomes of CABG, possibly due to blacks' high operative risk. Methods: We analyzed 71,949 CABG procedures performed between 2002 and 2005 at 93 academic medical centers participating in the University HealthSystem Consortium. In-hospital mortality was examined across hospital volume categories (very low, <100/ yr; low, 100-299/yr; medium, 300-499/yr; and high, >= 500/yr) via logistic regression. Results: In-hospital mortality was 2.0% in whites and 2.8% in blacks. Controlling for patient risk, geographic region, and proportion of African American patients treated at the hospital, the benefit of higher volume was substantial for blacks but only modest for whites (race-by-volume interaction; P = 0.033). Odds ratios of mortality for increasing volume categories (compared with very low volume) were 0.46, 0.37, and 0.47 among blacks but only 0.85, 0.77, and 0.75 among whites. Racial disparities in mortality existed mostly in very low-volume hospitals. The differential volume effect across the 2 racial groups seemed to be primarily driven by regional patterns, as the volume effect was much more pronounced in the South and the Midwest (region by volume interaction; P = 0.033). Conclusions: Blacks have greater reduction in mortality than whites by undergoing CABG at higher-volume hospitals, regardless of operative risk. Because of limited generalizability, these findings should be confirmed using more representative database.