The STS CABG composite measure: 2021 methodology update.

Abstract Background The original STS CABG composite measure uses a 1-year analytic cohort and 98% credible intervals (CrI) to classify better (3-star) or worse (1-star) than expected performance. As CABG volumes per STS participant (e.g., 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. Methods Among 990 STS Adult Cardiac Surgery Database participants, performance classifications for the CABG composite were studied using various analytic cohorts: single year (current approach, 2017); 3 years (2015-2017); last 450 cases within 3 years; most recent year (2017) plus additional cases to 450 total. We also compared 98% CrI with 95% CrI (used in other STS composite measures). Results Using 3 years of data and 95% CrI’s, 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%] versus n=59[6%]). Corresponding changes for 1-star participants were 6.5 percentage points and 133% (n=113[11.4%] versus n=48[4.9%]). These changes were particularly notable among lower volume ( Conclusions 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 ACSD participants. This revised methodology is also now consistent with other STS procedure composites.