Quality collaboratives improve quality of care at the hospital and collaborative levels, but less is understood about how such efforts affect patient-level disparities. This study evaluated how a quality improvement (QI) effort (increasing multiarterial grafting during coronary artery bypass grafting (CABG)) translated into populations which historically receive lower-quality care (females and patients of low socioeconomic status).

Retrospective cohort study.

All non-federal hospitals in the state of Michigan that perform cardiac surgery and participate in a statewide collaborative database (n=33).

Patients undergoing first-time, isolated CABG receiving at least two bypass grafts from 2011 to 2022 were identified.

Association of sex and socioeconomic status with multiarterial grafting was evaluated across the study period. The distressed community index (DCI), a socioeconomic ranking (0—not distressed, 100—severely distressed), was matched to the patient’s zip code. Hierarchical regression modelling was performed to associate DCI and sex with multiarterial grafting, incorporating patient factors and hospital and surgeon effects. A sex-surgery year and DCI-surgery year interaction term was performed to assess the change in the rate of multiarterial grafting.

A total of 40 322 patients underwent CABG at 33 centres with a median age of 66 years and 24% were female. The rate of multiarterial grafting was 15%, although lower among females (10% vs 17%) and the highest (vs lowest) DCI quartile (14% vs 18%). After risk adjustment, females were less likely to receive multiarterial grafting (OR_adj 0.51 (95% CI 0.45 to 0.58), padj 0.35 per 10-point increase (95% CI 0.24 to 0.51), p0.05).

Despite a large overall increase in multiarterial grafting due to QI efforts, females and patients with low socioeconomic status had lower rates of multiarterial grafting. QI efforts should be evaluated both overall and among patients who historically receive lower quality care to improve quality and equity.