title: Differences in complication rates among the centres in the SPACE study.
abstract: BACKGROUND
  Despite the high grade of standardisation of study protocols, there is still room for variability among the centres in specific treatment aspects. We evaluated the treatment risk in stent-protected angioplasty of the carotid versus endarterectomy (SPACE) associated with the specific patient enrollment rates of the centres.
  
  
  METHODS
  The analysed endpoints were ipsilateral stroke or death [primary outcome event (pOE)] and any stroke or death [secondary outcome event (sOE)] until 30 days after treatment. A binary logistic regression analysis with random effects was performed separately for each treatment arm. The centres were secondarily categorised in three classes: I) > or = 25 patients enrolled, II) ten to 24 patients and III) <10 patients and a hierarchic log linear model was fitted to test the three-way interaction of treatment, number of patients per class and outcome.
  
  
  RESULTS
  The random effects logistic regression analysis in the carotid artery stenting (CAS) arm proved a significant increase in pOE with decreasing number of patients enrolled (-0.0190 +/- 0.0085, p = 0.025, deviance 35.7 with 32 df), whereas no such effect was found in the carotid endartectomy (CEA) arm (-0.010 +/- 0.008, p = 0.24, deviance 39.78 with 32 df). In the log linear model, there was a significant interaction between treatment, number of patients per centre and sOE (p = 0.023). The odds ratios for sOE in the enrollment classes (CAS vs. CEA) were 0.98 (95% CI 0.50-1.94, p = 0.95) for class I, 1.13 (95% CI 0.47-2.77, p = 0.77) for class II and 11.56 (95% CI 1.40-253.45, p = 0.01) for class III centres.
  
  
  CONCLUSIONS
  Despite rigorous standardisation and quality requirements for operator qualification, there seemed to be a decrease in complication rate with increasing patient enrollment numbers in the CAS arm while this signal could not be detected in the CEA arm of SPACE.
authors.affiliation: Department of Neuroradiology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany. fiehler@uke.de
authors.forename: Jens
authors.initials: J
authors.lastname: Fiehler
authors.forename: Olav
authors.initials: O
authors.lastname: Jansen
authors.forename: Jürgen
authors.initials: J
authors.lastname: Berger
authors.forename: Hans-Henning
authors.initials: HH
authors.lastname: Eckstein
authors.forename: Peter A
authors.initials: PA
authors.lastname: Ringleb
authors.forename: Robert
authors.initials: R
authors.lastname: Stingele
mesh_terms: D000800:Angioplasty, Balloon / Q000009:adverse effects* / Q000706:statistics & numerical data; D016893:Carotid Stenosis / Q000628:therapy*; D002985:Clinical Protocols; D016894:Endarterectomy, Carotid / Q000009:adverse effects* / Q000706:statistics & numerical data; D006801:Humans; D016015:Logistic Models; D018579:Patient Selection; D012307:Risk Factors; D018401:Sample Size; D015607:Stents / Q000009:adverse effects* / Q000706:statistics & numerical data; D020521:Stroke / Q000453:epidemiology*; D016896:Treatment Outcome