The Society of Thoracic Surgeons Coronary Artery Bypass Graft Composite Measure: 2021 Methodology Update

The Society of Thoracic Surgeons (STS) original coronary artery bypass graft surgery (CABG) composite measure uses a 1-year analytic cohort and 98% credible intervals (CrI) to classify better than expected (3-star) performance or worse than expected (1-star) performance. As CABG volumes per STS participant (eg, hospital or practice group) have decreased, it has become more challenging to classify performance categories using this approach, especially for lower volume programs, and alternative approaches have been explored.

Among 990 STS Adult Cardiac Surgery Database participants, performance classifications for the CABG composite were studied using various analytic cohorts: 1 year (current approach, 2017); 3 years (2015 to 2017); last 450 cases within 3 years; and most recent year (2017) plus additional cases to 450 total. We also compared 98% CrI with 95% CrI (used in other STS composite measures).

Using 3 years of data and 95% CrIs, 113 of 990 participants (11.4%) were classified 1-star and 198 (20%) 3-star. Compared with 1-year analytic cohorts and 98% CrI, the absolute and relative increases in the proportion of 3-star participants were 14 percentage points and 233% (n = 198 [20%] vs n = 59 [6%]). Corresponding changes for 1-star participants were 6.5 percentage points and 133% (n = 113 [11.4%] vs n = 48 [4.9%]). These changes were particularly notable among lower volume (fewer than 199 CABG per year) participants. Measure reliability with the 3-year, 95% CrI modification is 0.78.

Compared with current STS CABG composite methodology, a 3-year analytic cohort and 95% CrI increases the number and proportion of better or worse than expected outliers, especially among lower-volume Adult Cardiac Surgery Database participants. This revised methodology is also now consistent with other STS procedure composites.