title: Impact of QRS morphology and duration on outcomes after cardiac resynchronization therapy: Results from the Resynchronization-Defibrillation for Ambulatory Heart Failure Trial (RAFT).
abstract: BACKGROUND
  The impact of QRS morphology and duration on the effectiveness of cardiac resynchronization therapy (CRT) has been usually assessed separately. The interaction between these 2 simple ECG parameters and their effect on CRT has not been systematically assessed in a large-scale clinical trial.
  
  
  RESULTS
  The Resynchronization-Defibrillation for Ambulatory Heart Failure Trial showed that implantable cardioverter defibrillator-CRT was associated with a significant reduction in the primary end point of all-cause mortality or heart failure hospitalization. For this substudy, we excluded patients in atrial fibrillation and those with a previous pacemaker. All baseline ECGs were reviewed by a panel of 3 experienced electrocardiographers. A total of 1483 patients were included in this study. Of these, 1175 had left bundle-branch block (LBBB) and 308 had non-LBBB. In patients with LBBB receiving implantable cardioverter defibrillator-CRT, there was a reduction in the primary outcome and in each individual component of the primary outcome. Furthermore, there was continuous relationship between QRS duration and extent of benefit. In patients with non-LBBB and QRS ≥160 ms, the hazard ratio for the primary outcome was 0.52 (0.29-0.96; P=0.033); in patients with QRS <160 ms, the hazard ratio was 1.38 (0.88-2.14; P=0.155).
  
  
  CONCLUSIONS
  In patients with LBBB, there was a continuous relationship between broader QRS and greater benefit from implantable cardioverter defibrillator-CRT. However, our data do not support the use of implantable cardioverter defibrillator-CRT in patients with non-LBBB, especially when the QRS duration is <160 ms. There may be some delayed benefit when the QRS is ≥160 ms, but this needs further investigation.
  
  
  BACKGROUND
  URL: http://www.clinicaltrials.gov. Unique identifier: NCT00251251.
authors.affiliation: Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario, Canada.
authors.forename: David H
authors.initials: DH
authors.lastname: Birnie
authors.forename: Andrew
authors.initials: A
authors.lastname: Ha
authors.forename: Lyall
authors.initials: L
authors.lastname: Higginson
authors.forename: Kiran
authors.initials: K
authors.lastname: Sidhu
authors.forename: Martin
authors.initials: M
authors.lastname: Green
authors.forename: François
authors.initials: F
authors.lastname: Philippon
authors.forename: Bernard
authors.initials: B
authors.lastname: Thibault
authors.forename: George
authors.initials: G
authors.lastname: Wells
authors.forename: Anthony
authors.initials: A
authors.lastname: Tang
mesh_terms: D000368:Aged; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D004554:Electric Countershock; D004562:Electrocardiography; D005260:Female; D006333:Heart Failure / Q000503:physiopathology / Q000628:therapy*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010045:Outpatients; D013318:Stroke Volume / Q000502:physiology*; D016896:Treatment Outcome
keywords: bundle-branch block; cardiac resynchronization therapy; electrocardiography