title: The benefit of cardiac resynchronization therapy and QRS duration: a meta-analysis.
abstract: BACKGROUND
  Cardiac resynchronization therapy (CRT) improves outcomes in patients with heart failure (HF) because of reduced left ventricular systolic function and a wide QRS complex. Whether this benefit is consistent across all degrees of QRS widening is unclear. We performed a meta-analysis of randomized clinical trials to evaluate the impact of QRS duration on the efficacy of CRT.
  
  
  RESULTS
  We searched MEDLINE and EMBASE databases for studies evaluating the efficacy of CRT in patients with HF. Only trials that reported subgroup data according to QRS duration were included. Hazard ratios (HR) with 95% confidence interval (CI) were calculated using a random effects model. Five trials involving 6,501 patients (4,437 with QRS ≥ 150 ms and 2,064 with QRS < 150 ms) were included. Three trials, enrolling patients with mild to moderate HF, compared CRT-implantable cardioverter defibrillator with CRT, whereas CRT versus medical therapy was compared in the other 2 trials, which included patients with advanced HF. Based on the pooled estimate across the 5 studies, CRT significantly decreased the primary endpoint of death or hospitalization for HF in patients with QRS ≥ 150 ms (HR = 0.58, 95% CI: 0.50-0.68; P < 0.00001), but not in patients with QRS < 150 ms (HR = 0.95, 95% CI: 0.83-1.10; P = 0.51). These results were consistent across all degrees of HF severity.
  
  
  CONCLUSIONS
  The benefit of CRT seems to be dependent on QRS duration. Available data suggest a significant benefit associated with CRT in patients with QRS ≥ 150 ms, but not in patients with QRS < 150 ms. Further studies are needed to identify patients with QRS < 150 ms who might benefit from CRT.
authors.affiliation: Department of Medicine, Cardiovascular Section, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA. stavrosstavrakis@ouhsc.edu
authors.forename: Stavros
authors.initials: S
authors.lastname: Stavrakis
authors.forename: Ralph
authors.initials: R
authors.lastname: Lazzara
authors.forename: Udho
authors.initials: U
authors.lastname: Thadani
mesh_terms: D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D006333:Heart Failure / Q000503:physiopathology / Q000628:therapy*; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D016032:Randomized Controlled Trials as Topic / Q000379:methods; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000503:physiopathology / Q000628:therapy; D016277:Ventricular Function, Left / Q000502:physiology*