Institutional variation in early mortality following isolated coronary artery bypass graft surgery

Background: Thirty-day mortality following coronary artery bypass grafting (CABG) is a widely accepted marker for quality of care. Although surgical mortality has declined, the utility of this measure to profile quality has not been questioned. We assessed the institutional variation in risk-standardised mortality rates (RSMR) following isolated CABG within Australia and New Zealand (ANZ).

Methods: We used an administrative dataset from all public and most private hospitals across ANZ to capture all isolated CABG procedures recorded between 2010 and 2015. The primary outcome was all-cause death occurring in-hospital or within 30-days of discharge. Hospital-specific RSMRs and 95% CI were estimated using a hierarchical generalised linear model accounting for differences in patient characteristics.

Results: Overall, 60,953 patients (mean age 66.1 ± 10.1y, 18.7% female) underwent an isolated CABG across 47 hospitals. The observed early mortality rate was 1.69% (n = 1029) with 81.8% of deaths recorded in-hospital. The risk-adjustment model was developed with good discrimination (C-statistic = 0.81). Following risk-adjustment, a 3.9-fold variation was observed in RSMRs among hospitals (median:1.72%, range:0.84-3.29%). Four hospitals had RSMRs significantly higher than average, and one hospital had RSMR lower than average. When in-hospital mortality alone was considered, the median in-hospital RSMR was 1.40% with a 5.6-fold variation across institutions (range:0.57-3.19%).

Conclusions: Average mortality following isolated CABG is low across ANZ. Nevertheless, in-hospital and 30-day mortality vary among hospitals, highlighting potential disparities in care quality and the enduring usefulness of 30-day mortality as an outcome measure. Clinical and policy interventions, including participating in clinical quality registries, are needed to standardise CABG care.