title: Association of center volume with outcomes: analysis of verified data of European Association for Cardio-Thoracic Surgery Congenital Database.
abstract: BACKGROUND
  The relation between surgical volumes and outcome in congenital heart surgery (CHS) was investigated with no clear conclusions. We sought to quantify the relationship between surgical volume and surgical performance defined as the relation between outcome and Society of Thoracic Surgeons-European Association for Cardio-Thoracic Surgery Congenital Heart Surgery (STAT) Mortality Score and The Society of Thoracic Surgeons (STS) Morbidity Score.
  
  
  METHODS
  We have used only the verified data of the European Association for Cardio-Thoracic Surgery Congenital Database. The verified dataset consists of 17,861 procedures performed in 23 congenital heart surgery centers between 2003 and 2011. The centers were divided into 4 volume-related groups with annual caseload of below 150, 150 to 250, 250 to 350, and over 350. Stepwise logistic regression was used to calculate the ratio between volume and mortality, as well as between volume and onset of complications. The relations between volume and STAT Mortality Score, and STS Morbidity Score were evaluated using the analysis of variance test. The performance was calculated as the following: 100 - observed mortality/STAT Mortality Score; and 100 - observed complications/STS Morbidity Score.
  
  
  RESULTS
  The study showed no relation between volume and raw mortality (p = 0.94) and between volume and complications (p = 0.6). The STAT Mortality Score and STS Morbidity Score were higher in larger volume centers (p < 0.001). Surgical performances measured as related to mortality and morbidity were higher at high-volume centers (R(2) = 0.95 and R(2) = 0.92).
  
  
  CONCLUSIONS
  Our analysis suggests that after adjustment for case mix higher programmatic volume is associated with lower rates of mortality and morbidity. The small- and medium-volume centers have higher rates of major complications. When complications occurred the chance of rescue is higher in large-volume centers.
authors.affiliation: Department of Cardiothoracic Surgery, The Children's Memorial Health Institute, Warsaw, Poland. Electronic address: ankansy@wp.pl.
authors.forename: Andrzej
authors.initials: A
authors.lastname: Kansy
authors.affiliation: Department of Cardiovascular Surgery, University Hospital Groningen, Netherlands.
authors.forename: Tjark
authors.initials: T
authors.lastname: Ebels
authors.affiliation: Department of Cardiovascular Surgery, German Heart Centre, Munich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Schreiber
authors.affiliation: Department of Cardiothoracic Surgery, The Children's Memorial Health Institute, Warsaw, Poland.
authors.forename: Zdzislaw
authors.initials: Z
authors.lastname: Tobota
authors.affiliation: Department of Cardiothoracic Surgery, The Children's Memorial Health Institute, Warsaw, Poland.
authors.forename: Bohdan
authors.initials: B
authors.lastname: Maruszewski
mesh_terms: D006348:Cardiac Surgical Procedures / Q000706:statistics & numerical data*; D002648:Child; D002675:Child, Preschool; D016208:Databases, Factual; D005060:Europe / Q000453:epidemiology; D005260:Female; D005500:Follow-Up Studies; D006330:Heart Defects, Congenital / Q000401:mortality / Q000601:surgery*; D017052:Hospital Mortality / Q000639:trends; D006761:Hospitals / Q000706:statistics & numerical data*; D006801:Humans; D008297:Male; D017063:Outcome Assessment, Health Care; D012189:Retrospective Studies; D012955:Societies, Medical; D013903:Thoracic Surgery