Effect of Hospital and Surgeon Procedure Volumes on the Incidence of Intraoperative Conversion During Off-Pump Coronary Artery Bypass Grafting

Intraoperative conversion to cardiopulmonary bypass with its subsequent high mortality is a major concern associated with off-pump coronary artery bypass grafting (OPCAB). The impact of procedure volume on the incidence of intraoperative conversion, however, is poorly defined. This study therefore evaluated the effect of procedure volume on the incidence of conversion in OPCAB using nationwide data. We analyzed 31,361 patients who underwent primary, nonemergent, isolated OPCAB during 2013–2016 reported in the Japan Cardiovascular Surgery Database. Hospitals (n = 548) and surgeons (n = 1315) were divided into tertile categories (low-, medium-, and high volumes) based on the total number of isolated coronary artery bypass grafting (CABG). Hierarchical logistic regression analysis, including 22 preoperative factors and hospital and surgeon CABG volumes, was used to assess the relation between procedure volume and the risk of conversion due to bleeding/hemodynamic instability. There were 797 (2.5%) intraoperative conversions due to bleeding/hemodynamic instability. Risk-adjusted odds ratios for conversion were significantly lower in some combined hospital/surgeon CABG volume categories than in the reference category. Hospital/surgeon volumes and their odds ratio (95% confidence interval) were as follows: low/low 1.00 (reference); medium/low 0.62 (0.39–0.96); high/low 0.47 (0.27–0.81); high/high 0.58 (0.38–0.89). There was a lower risk of conversion in medium- and high-volume than low-volume hospitals, especially among low-volume surgeons. Procedure volume is associated with the incidence of conversion during OPCAB. Among low-volume surgeons, hospital CABG volume significantly reduces conversion in a volume-dependent manner. These findings will be useful for safety training of OPCAB surgeons.