Effect of institutional case volume on mid-term mortality after coronary artery bypass grafting surgery.

OBJECTIVE The impact of center case volume on mid-term postoperative outcome after coronary artery bypass grafting surgery (CABG) is still controversial and requires investigation. The aim of this study was to compare mid-term survival after CABG according to the institutional annual CABG case volume. METHODS Adult patients (≥ 18 years) who underwent CABG from 2009 to 2016 were identified by searching National Health Insurance database of Korea for CABG procedure codes. Hospitals were classified into three groups based on annual case volume; low-volume centers (  50 cases/year). RESULTS A total of 22,575 CABG were performed in 95 centers during the study period, and 14,697 (65.1%) cases performed at 15 high-volume centers, 5,262 (23.3%) cases at 26 medium-volume centers, and 2,616 (11.6%) cases at 54 low-volume centers. The overall 1-year mortality rate was the lowest in high-volume centers (6.5%), followed by medium-volume centers (10.6%) and low-volume centers (15.2%). Logistic regression identified medium-volume centers (adjusted OR 1.30 [95% CI 1.15-1.49], P < 0.01) and low-volume centers (adjusted OR 1.75 [95% CI 1.51-2.03], P < 0.01) as risk factors for 1-year mortality after CABG compared to high-volume centers. In the Cox proportional hazard model, low- and medium-volume centers were significantly risk factors for poor survival (adjusted HR 1.41 [95% CI 1.31-1.54], P < 0.01 and HR 1.26 [95% CI 1.17-1.35], P < 0.01 for low- and medium-volume centers, respectively). CONCLUSIONS Higher institutional case volume of CABG was associated with lower mid-term mortality.