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The Relationship Between Hospital CABG Volume and Multiple Dimensions of CABG Quality
David M. Shahian1, Sean O'Brien2, Sharon-Lise Normand3, Eric Peterson2, Fred Edwards4; 1Massachusetts General Hospital, Boston, MA; 2Duke Clinical Research Institute, Durham, NC; 3Harvard Medical School, Boston, MA; 4University of Florida, Jacksonville, FL
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Objective: Previous research suggests a weak relationship between hospital CABG volume and risk-adjusted mortality, but the latter is only one dimension of overall CABG quality. This study examines the relationship between hospital CABG volume and each of the four domains of the STS CABG composite score, a multidimensional quality measure consisting of 11 individual NQF-endorsed performance metrics.
Methods: The study population consisted of 144, 526 patients who underwent isolated CABG between 1/1/07 and 12/31/07 at one of 733 hospitals participating in the STS Database. Hospitals were grouped into 6 volume categories based on total number of procedures that included a CABG, while the analysis population consisted only of isolated CABG procedures.
Endpoints included mortality; any major morbidity (stroke, renal failure, sternal infection, reoperation, and/or prolonged ventilation); failure to receive an IMA; and failure to use all indicated medications. Hierarchical logistic regression models were used to assess the association between volume categories and each endpoint, adjusting for variables in the 2008 STS CABG risk model.
Results: Unadjusted outcomes did not differ significantly across volume categories for morbidity or medications. Unadjusted mortality ranged from 2.6% (95% CI 2.2-3.0) for hospitals performing < 100 CABG annually to 1.7% (95% CI 1.5-1.8) for hospitals performing 450+ cases (p < 0.001). Failure to perform an IMA ranged from 6.9% (95% CI 5.7, 8.0) for hospitals in the 100-149 CABG group to 5.4% (95% CI 4.7, 6.2) for hospitals performing 300-449 procedures (p = 0.0442). The adjusted results for each volume category were compared against the results for hospitals performing 450+ cases (Table). Only the 95% CI of the odds ratios for mortality excluded 1.00, and the results were most striking for hospitals in the <100 CABG category. When the four endpoints were aggregated into a single composite endpoint, only 1% of the variation in composite score was explained by volume.
Conclusion: Of the four domains of CABG quality that constitute the STS composite CABG score, only mortality demonstrates a statistically significant volume-outcome association. However, this relationship is weak, and it is most apparent at the extremes of volume.


Volume Category Number of Hospitals Number ofPatients Adjusted Odds Ratios (95% Confidence Intervals)
Mortality Morbidity IMA Failure Med Failure
≥450 92 47147 reference = 1.00 reference = 1.00 reference = 1.00 reference = 1.00
300-449 114 31585 1.17(1.01, 1.35) 0.91(0.73, 1.12) 0.87(0.72, 1.06) 1.03(0.90, 1.18)
200-299 157 30209 1.31(1.14, 1.51) 1.06(0.87, 1.30 0.92(0.76, 1.10) 1.02(0.90, 1.16)
150-199 108 14789 1.14(0.96, 1.35) 0.99(0.79, 1.23) 0.91(0.74, 1.11) 1.00(0.87, 1.15)
100-149 128 12740 1.29(1.08, 1.53) 1.11(0.90, 1.38) 0.88(0.72, 1.07) 1.03(0.89, 1.18)
<100 134 8056 1.49(1.24, 1.80) 1.15( 0.92, 1.43) 0.99(0.81, 1.20) 1.09(0.94, 1.26)

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