Shop for quality or volume? Volume, quality, and outcomes of coronary artery bypass surgery

Abstract

Background: Care from high-volume centers or surgeons has been associated with lower mortality rates in coronary artery bypass surgery, but how volume and quality of care relate to each other is not well understood.

Objective: To determine how volume and differences in quality of care influence outcomes after coronary artery bypass surgery.

Design: Observational cohort.

Setting: 164 hospitals in the United States.

Patients: 81,289 patients 18 years or older who had coronary artery bypass grafting from 1 October 2003 to 1 September 2005.

Measurements: Hospital and surgeon case volumes were estimated by using a data set. Quality measures were defined by whether patients received specific medications and by counting the number of measures missed. Hierarchical models were used to estimate effects of volume and quality on death and readmission up to 30 days.

Results: After adjustment for clinical factors, lowest surgeon volume and highest hospital volume were associated with higher mortality rates and lower readmission risk, respectively. Patients who did not receive aspirin (odds ratio, 1.89 [95% CI, 1.65 to 2.16) or beta-blockers (odds ratio, 1.29 [CI, 1.12 to 1.49]) had higher odds for death, after adjustment for clinical risk factors and case volume. Adjustment for individual quality measures did not alter associations between volume and readmission or death. However, if no quality measures were missed, mortality rates at the lowest-volume centers (adjusted mortality rate, 1.05% [CI, 0.81% to 1.29%]) and highest-volume centers (adjusted mortality rate, 0.98% [CI, 0.72% to 1.25%]) were similar.

Limitation: Because administrative data were used, the quality measures may not replicate measures collected through chart abstraction.

Conclusion: Maximizing adherence to quality measures is associated with improved mortality rates, independent of hospital or surgeon volume.

Primary funding source: California HealthCare Foundation.

Figure 1. Effects of hospital case volume and missed quality measures on mortality

Adjusted mortality of patients undergoing coronary bypass surgery by quartile of hospital volume and count of missed quality measures. A strong association between the number of quality measures missed and mortality across all quartiles of volume is observed, with mortality similar across quartiles of hospital case volume if no quality measures are missed. Models adjusted for age, gender, DRG predicted mortality, congestive heart failure, hypertension, neurological disorders, diabetes with complications, renal failure, coagulopathy, deficiency anemia, and whether or not an internal mammary graft was used during the procedure, the volume and number of missed quality measures as well as for the interaction between volume and number of missed quality measures.

Figure 2. Effects of surgeon case volume and missed quality measures on mortality

Adjusted mortality of patients undergoing coronary bypass surgery by quartile of surgeon volume and count of missed quality measures. As for hospital volume, strong association between the number of quality measures missed and mortality across all quartiles of surgeon volume is observed, with mortality similar even for lowest volume surgeons if no quality measures are missed. Models adjusted for age, gender, DRG predicted mortality, congestive heart failure, hypertension, neurological disorders, diabetes with complications, renal failure, coagulopathy, deficiency anemia, and whether or not an internal mammary graft was used during the procedure, the volume and number of missed quality measures as well as for the interaction between volume and number of missed quality measures.