Physician and hospital volumes are important determinants of outcome for many surgical procedures and medical conditions. The association between surgical case volume and outcome after coronary artery bypass graft (CABG) surgery has been extensively studied. Many of these stud-ies have demonstrated that hospitals and surgeons with higher case volumes have lower mortality rates. These findings have led to the development of guidelines by the American Heart Association/American College of Cardiology specifying the minimum number of procedures performed annually by cardiac surgeons. The selective referral of patients undergoing high-risk surgical procedures, such as CABG surgery, has been suggested to have the potential to significantly lower mortality rates by reducing the number of “potentially avoidable deaths. Limited regionalization of CABG care, accomplished through the Certificate of Need Regulation at the state level, is associated with 84% higher hospital case volumes and 22% lower risk-adjusted mortality rates. Although many studies have examined the association between volume and outcome for conventional CABG surgery, no other study has explored the surgeon volume-outcome association for CABG surgery performed without the use of cardiopulmonary bypass (CPB) [ie, off-pump CABG surgery].
Conventional CABG surgery (ie, “on-pump” surgery) is performed after the heart has been arrested using CPB. CPB allows the cardiac surgeon to perform coronary anastomoses in a bloodless and motionless surgical field. However, CPB initiates a systemic inflammatory response, generates microemboli and macroemboli, and may be responsible for much of the morbidity associated with conventional CABG surgery. The incidence of morbidity following CABG surgery, based on data from the Society of Thoracic Surgery database for 170,895 patients, is 35.6%.Off-pump CABG surgery may avoid many of the adverse effects associated with CPB. However, surgery on a beating heart is technically more difficult and may be associated with suboptimal surgical exposure and a greater degree of hemodynamic instability than conventional CABG surgery. Despite the fact that off-pump surgery is technically more difficult, the use of the off-pump technique is growing rapidly. In New York State, the percentage of CABG procedures performed off-pump increased from 3% in 1997 to 27% in 2000.
The widespread adoption of the off-pump approach is relatively new, and there are few data on the surgeon volume-outcome association for off-pump CABG surgery. Because off-pump CABG surgery is a “new” procedure and is technically more challenging than on-pump CABG surgery for cardiac surgeons, it is anticipated that the outcome benefit associated with higher surgeon case volumes (“practice makes perfect”) is greater for off-pump CABG surgery than for on-pump CABG surgery. Therefore, we conducted a population-based study using the New York State Cardiac Surgery database to determine whether the surgeon “volume effect” for off-pump surgery is significantly different than that for on-pump surgery. The existence of a strong volume-outcome association for off-pump CABG surgery may have important policy implications for surgeons performing a low volume of procedures and for those currently not performing off-pump CABG surgery.