title: Is hospital procedure volume a reliable marker of quality for coronary artery bypass surgery? A comparison of risk and propensity adjusted operative and midterm outcomes.
abstract: BACKGROUND
  Worse operative mortality has been reported for hospitals with low versus high coronary artery bypass grafting surgery volumes. Despite a lack of comparisons beyond the early postoperative period and evidence of surgeon-volume confounding, some have suggested that regionalization of coronary artery bypass grafting in favor of high volume institutions is warranted.
  
  
  METHODS
  We retrospectively compared operative mortality and 3-year survival in coronary artery bypass grafting patients (2001 to 2003) at a low-volume hospital (n = 504; 160 per year [median]) versus a high-volume hospital (n = 1,410; 487 per year) served by the same high-volume surgeon team. Covariate risk adjustment was done via multivariate and propensity modeling.
  
  
  RESULTS
  The two hospital cohorts exhibited multiple demographic and risk factor differences. Unadjusted low-volume hospital vs high-volume hospital operative mortality was similar overall (2.38% vs 2.98%; p = 0.59) with nearly identical Society of Thoracic Surgeons observed-to-expected ratios (0.83 vs 0.82), irrespective of preoperative risk category. Hospital volume did not predict operative mortality (odds ratio, 95% confidence interval = 0.82; p = 0.602). At follow-up, a total of 28 low-volume hospital deaths (5.6%) and 135 high-volume hospital deaths (9.6%) occurred at similar surgery-to-death intervals (p = 0.7). Unadjusted 0 to 3-year survival was significantly worse for high-volume hospitals (risk ratio = 1.59; 1.06 to 2.39; p = 0.026). Yet procedure volume was not independently associated with worse midterm survival after covariate (risk ratio = 1.28; 0.84 to 1.96; p = 0.247) or propensity score (risk ratio = 1.11; 0.72 to 1.71; p = 0.648) adjustment.
  
  
  CONCLUSIONS
  Hospital and surgeon volume effects on coronary artery bypass grafting outcomes are interdependent, and therefore hospital coronary artery bypass grafting volume per se is not a reliable marker of quality. Instead, outcome quality markers should rely on thorough risk-adjustment based on detailed clinical databases, possibly including annual and cumulative surgeon volume.
authors.affiliation: Division of Cardiovascular Surgery, St. Vincent Mercy Medical Center, Toledo, Ohio 43608, USA.
authors.forename: Anoar
authors.initials: A
authors.lastname: Zacharias
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Schwann
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Riordan
authors.forename: Samuel J
authors.initials: SJ
authors.lastname: Durham
authors.forename: Aamir
authors.initials: A
authors.lastname: Shah
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Papadimos
authors.forename: Milo
authors.initials: M
authors.lastname: Engoren
authors.forename: Robert H
authors.initials: RH
authors.lastname: Habib
mesh_terms: D000368:Aged; D002983:Clinical Competence; D001026:Coronary Artery Bypass / Q000592:standards* / Q000706:statistics & numerical data*; D003324:Coronary Artery Disease / Q000601:surgery; D005260:Female; D017052:Hospital Mortality; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D008875:Middle Aged; D019984:Quality Indicators, Health Care; D012189:Retrospective Studies; D020379:Risk Adjustment; D016896:Treatment Outcome