Hospital variation in readmission after coronary artery bypass surgery in California

Background: Readmissions are common after coronary artery bypass grafting (CABG) surgery and account for a significant percentage of hospital healthcare costs. Readmission rates also vary widely between hospitals, but the reasons for this variation have not been studied previously. Methods and Results: We linked 2009 California CABG clinical registry data to hospital discharge data for 2009 and 2010 to identify 30-day readmissions for all patients undergoing isolated CABG surgery. Both standard and hierarchical logistic models were developed to predict readmission risk and explore sources of hospital readmission variation. Among 11 823 patients discharged alive after isolated CABG in 2009, 1565 (13.2%) patients were readmitted within 30 days of surgery. Heart failure and postoperative infections were the most frequent reasons for readmission (15.3% and 12.9%, respectively). Multiple patient risk factors, including age, sex, and lower zip code-level median household income, were significant predictors of readmission (all adjusted odds ratios >1.0; P<0.05). The readmission rates among the 119 hospitals performing CABG varied from 0% to 26.9%. Compared with hospitals in lower quartiles for readmission, hospitals in higher quartiles had a significantly higher readmission rates due to circulatory diseases, infections, complications for surgical and medical care and digestive diseases (all P<0.05). In a hierarchical model, including several hospital characteristics, hospital-level variables did not predict readmission risk (all P>0.05, with an intraclass correlation of 0.004 for hospitals). Conclusions: California hospitals performing CABG surgery vary widely in 30-day readmission rates. Patient demographic and clinical risk factors, rather than measured hospital characteristics, accounted for most of the observed hospital-level variation in CABG readmissions.