Incidence, timing and variation in unplanned readmissions within 30-days following isolated coronary artery bypass grafting.

Background: Coronary Artery Bypass Grafting (CABG) is the most common cardiac surgery, yet little is known about unplanned readmissions after CABG despite increasing clinical and policy focus on reducing readmissions. We assessed the incidence, timing, and reasons for unplanned readmission within 30 days of CABG and evaluated for variation in readmission rates across hospitals in Australia and New Zealand (ANZ). Method: We identified isolated CABG procedures from 2013 to 2017 across all public and most private hospitals in ANZ. The primary outcome was unplanned (acute) readmissions within 30-days of discharge. Hospital specific risk standardised readmission rates (RSRRs) and 95% CI were estimated using a hierarchical generalized linear model accounting for differences in patient characteristics. Results: 52,104 patients (mean age 66.1 ± 9.9 years, 17.6 % female, 30.7 % acute) were included. The 30-day unplanned readmission rate was 12.7 % (n = 6,613) and was higher following urgent surgery (16.2 %, n = 2,595). Readmission rates peaked on days 2-4 with a median time to readmission of 9 (IQR: 4-17) days. Procedural complications and chest pain were the most common diagnoses on readmission. Risk adjustment model demonstrated satisfactory performance (C-statistic = 0.62). The median RSRR was 12.8 % (range: 6.1-20.3 %) across 37 hospitals. Only one hospital had its RSRR estimate lower than average and no hospitals had higher than average RSRR. Conclusion: One-in-8 patients undergoing CABG experienced an unplanned readmission within 30-day, rising to one-in-6 following urgent CABG. There was little statistically significant institutional variation in RSRR. Nevertheless, many readmissions are likely related to care quality and potentially preventable, highlighting scope for clinical and policy interventions to reduce readmissions.