title: Aortic valve replacement: using a statewide cardiac surgical database identifies a procedural volume hinge point.
abstract: BACKGROUND
  Expanding therapies for aortic stenosis have focused on high-risk and inoperable patients, suggesting that an evaluation of outcomes of conventional aortic valve replacement (AVR) or AVR and coronary artery bypass grafting (CABG) is timely and warranted.
  
  
  METHODS
  Outcomes for 6,270 AVR (3,487) or AVR/CABG (2,783) procedures performed in Michigan (2008-2011) were analyzed using a statewide cardiothoracic surgical database. Hospital and surgeon volume-outcome relationships were assessed.
  
  
  RESULTS
  Independent predictors of early mortality (all p < 0.05) included age, female sex, predicted risk of mortality, and hospital volume, with a hinge point of a 4-year volume of 390 procedures (high-volume hospital [HVH], 2.41% versus low-volume hospital [LVH], 4.34%; p < 0.001). At this hinge point, observed to expected ratio (O/E) for operative mortality after AVR was lower in HVHs for patients with a predicted risk of mortality (PRoM) greater than 4.7%. In contrast, no surgeon-volume outcome relationship was identified, even when stratified by preoperative patient-risk profile. With respect to other measures, HVHs reported lower rates of prolonged ventilation (24.9% versus LVH, 30.9%; p < 0.001), postoperative transfusion (46.1% versus LVH, 59.0%; p < 0.001), pneumonia (6.6% versus LVH, 9.0%; p = 0.01), and multisystem organ failure (0.7% versus LVH, 1.8%; p = 0.012).
  
  
  CONCLUSIONS
  This population-based analysis suggests that volume-outcome relationships exist for AVR. The predominant effect on mortality appears based on the setting of the procedure and occurs primarily in the high-risk patient. These results provide an opportunity to review approaches for high-risk patients undergoing AVR, including resource availability and system experience as the spectrum of treatment options expands to transcatheter therapies.
authors.affiliation: University of Michigan Medical Center, Ann Arbor, Michigan. Electronic address: hjpatel@med.umich.edu.
authors.forename: Himanshu J
authors.initials: HJ
authors.lastname: Patel
authors.forename: Morley A
authors.initials: MA
authors.lastname: Herbert
authors.forename: Daniel H
authors.initials: DH
authors.lastname: Drake
authors.forename: Eric C
authors.initials: EC
authors.lastname: Hanson
authors.forename: Patricia F
authors.initials: PF
authors.lastname: Theurer
authors.forename: Gail F
authors.initials: GF
authors.lastname: Bell
authors.forename: Richard L
authors.initials: RL
authors.lastname: Prager
mesh_terms: D000368:Aged; D001021:Aortic Valve / Q000601:surgery*; D001024:Aortic Valve Stenosis / Q000601:surgery*; D016208:Databases, Factual; D005260:Female; D019918:Heart Valve Prosthesis Implantation / Q000706:statistics & numerical data; D061847:Hospitals, High-Volume / Q000706:statistics & numerical data; D061846:Hospitals, Low-Volume / Q000706:statistics & numerical data; D006801:Humans; D008297:Male; D008824:Michigan
keywords: 35; 4