title: Abnormal conduction increases risk of adverse outcomes from right ventricular pacing.
abstract: OBJECTIVE
  The purpose of this study was to determine whether QRS duration or morphology increased the risk of adverse outcome in the DAVID (Dual Chamber and VVI Implantable Defibrillator) trial.
  
  
  BACKGROUND
  The DAVID trial found an increased risk of the combined end point of death and new or worsening congestive heart failure (CHF) in defibrillator recipients who were paced DDDR-70 versus VVI-40.
  
  
  METHODS
  We analyzed the combined end point in patients with abnormal QRS duration (AbQRS) (> or =110 ms) compared with those with normal QRS duration (NQRS) (<110 ms).
  
  
  RESULTS
  The QRS data were available for 496 of the 506 patients enrolled in the trial, including 223 patients with NQRS (45%) and 273 patients with AbQRS (55%). In patients in whom defibrillators were programmed to pace infrequently (VVI-40), having an NQRS or AbQRS was not an indicator of increased risk of adverse outcome. However, among patients in whom defibrillators were programmed in a manner that promoted more frequent ventricular pacing (DDDR-70), there was a significant adverse interaction with AbQRS; this combination was independently associated with a higher risk for developing CHF or death (p = 0.017).
  
  
  CONCLUSIONS
  Although patients with AbQRS tended to have other risk factors associated with poor outcome, the interaction of QRS duration with ventricular pacing (DDDR-70) independently contributed to a worse outcome and therefore, was a marker of patients in whom such treatment may be harmful. This should not imply that right ventricular pacing in NQRS patients is safe but rather that pacing in the context of an AbQRS is probably best avoided.
authors.affiliation: Marshfield Clinic and Research Foundation, Marshfield, Wisconsin, USA. hayes.john@marshfieldclinic.org
authors.forename: John J
authors.initials: JJ
authors.lastname: Hayes
authors.forename: Arjun D
authors.initials: AD
authors.lastname: Sharma
authors.forename: John C
authors.initials: JC
authors.lastname: Love
authors.forename: John M
authors.initials: JM
authors.lastname: Herre
authors.forename: Anna O
authors.initials: AO
authors.lastname: Leonen
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Kudenchuk
mesh_terms: D002304:Cardiac Pacing, Artificial / Q000009:adverse effects* / Q000379:methods; D017147:Defibrillators, Implantable; D018450:Disease Progression; D004562:Electrocardiography; D006329:Heart Conduction System / Q000503:physiopathology*; D006333:Heart Failure / Q000209:etiology* / Q000503:physiopathology*; D006352:Heart Ventricles; D006801:Humans; D015337:Multicenter Studies as Topic; D016016:Proportional Hazards Models; D016032:Randomized Controlled Trials as Topic; D018570:Risk Assessment; D016019:Survival Analysis