title: Association between QRS duration and outcome with cardiac resynchronization therapy: a systematic review and meta-analysis.
abstract: OBJECTIVE
  We conducted a systematic review and meta-analysis of randomized and observational studies to evaluate the associations between QRS duration (QRSd) at baseline or in follow-up and outcomes with cardiac resynchronization therapy (CRT).
  
  
  METHODS
  We searched online databases to December 2010 and included 6 randomized controlled trials (RCTs) and 38 observational studies. Outcomes included clinical/functional response, left ventricular (LV) remodeling, hospitalizations and mortality.
  
  
  RESULTS
  In RCTs, a benefit of CRT was evident only in patients with QRSd >150ms. In observational studies, those meeting either clinical or remodeling CRT response definitions had both wider pooled baseline QRSd and significantly more QRS narrowing with CRT than non-responders.
  
  
  CONCLUSIONS
  RCTs demonstrate that benefit with CRT appears restricted to those with baseline QRSd wider than 150ms. Both wider baseline QRS and more QRS narrowing are associated with CRT response in observational studies. Electrocardiographic QRSd plays an important role in CRT patient selection and follow-up.
authors: Libin Cardiovascular Institute of Alberta, University of Calgary, Canada.
authors: Adam R
authors: AR
authors: Bryant
authors: Stephen B
authors: SB
authors: Wilton
authors: Michael P
authors: MP
authors: Lai
authors: Derek V
authors: DV
authors: Exner
mesh_terms: D058406:Cardiac Resynchronization Therapy / Q000706:statistics & numerical data*; D015897:Comorbidity; D004562:Electrocardiography / Q000706:statistics & numerical data*; D006333:Heart Failure / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control*; D006801:Humans; D015995:Prevalence; D011379:Prognosis; D018570:Risk Assessment; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis* / Q000453:epidemiology / Q000517:prevention & control*