Effects of institutional volumes on operative outcomes for aortic root replacement in North America

Abstract

Objectives: Hospital procedure volume has been strongly associated with postoperative mortality for a number of complex cardiovascular procedures. Although not yet described, a similar relationship might be expected for surgical procedures involving the aortic root and/or ascending aorta. The present study sought to evaluate the relationship between the volume of aortic root replacement procedures and the operative results for centers in North America.

Methods: Patient-level data for 13,358 elective aortic root and aortic valve-ascending aortic procedures performed from 2004 through 2007 were obtained from 741 North American hospitals participating in the Society of Thoracic Surgeons Adult Cardiac Surgery Database. Marginal logistic regression modeling was used for risk adjustment. The hospital procedure volume was the primary predictor variable. Patient demographics, comorbid conditions, and operative characteristics were included as the predictor variables for risk adjustment. The primary outcome measures included unadjusted operative mortality and adjusted odds ratio for mortality.

Results: The preoperative patient risk profiles were similar at all center volume levels, and the overall unadjusted operative mortality was 4.5%. The unadjusted operative mortality increased with decreasing case volume, from 3.4% in the highest volume centers to 5.8% in the lowest volume centers. Whether hospital volume was assessed as a categorical or continuous variable, its relationship with the adjusted odds ratio for mortality was nonlinear. A negative association was seen between the hospital procedural volume and adjusted odds ratio for mortality (P < .001) that was most pronounced among hospitals performing fewer than 30 to 40 procedures annually.

Conclusions: Patients undergoing elective aortic root or combined aortic valve-ascending aortic surgery at North American hospitals that performed fewer than 30 to 40 of such procedures annually have greater risk-adjusted mortality than those undergoing surgery in higher volume hospitals. Causative factors for this inverse association between hospital volume and mortality deserve additional analysis.