title: Effect of heart rate on the intrinsic and the ventricular-paced QRS duration.
abstract: BACKGROUND
  We evaluated the effect of heart rate on the intrinsic and the ventricular-paced QRS duration in implanted device recipients with normal or reduced left ventricular ejection fraction (EF).
  
  
  METHODS
  We studied 239 outpatients with preserved intrinsic ventricular activation and normal (n=92) or reduced (n=147) EF who had apical (RVA) or mid-septal (RVS) right ventricular lead position. The QRS duration was measured at baseline and during atrial-based pacing at increased heart rate to ensure intrinsic or ventricular-paced QRS activation.
  
  
  RESULTS
  The heart rate increase shortened the intrinsic QRS only in patients with normal EF, and further prolonged the ventricular-paced QRS in patients with reduced EF and either narrow or wide QRS (p<0.001), irrespective of RVA or RVS pacing (p<0.01).
  
  
  CONCLUSIONS
  Heart rate increase is associated with further QRS prolongation in patients with reduced EF, regardless of RVA or RVS pacing site.
authors.affiliation: Cardiology Department, Patras University Hospital, 26500 Rion, Patras, Greece. Electronic address: chil@otenet.gr.
authors.forename: John
authors.initials: J
authors.lastname: Chiladakis
authors.affiliation: Cardiology Department, Patras University Hospital, 26500 Rion, Patras, Greece.
authors.forename: Andreas
authors.initials: A
authors.lastname: Kalogeropoulos
authors.affiliation: Cardiology Department, Patras University Hospital, 26500 Rion, Patras, Greece.
authors.forename: Fani
authors.initials: F
authors.lastname: Zagkli
authors.affiliation: Cardiology Department, Patras University Hospital, 26500 Rion, Patras, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Chouchoulis
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001145:Arrhythmias, Cardiac / Q000175:diagnosis / Q000503:physiopathology* / Q000517:prevention & control*; D058406:Cardiac Resynchronization Therapy / Q000379:methods*; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013318:Stroke Volume; D016896:Treatment Outcome; D018487:Ventricular Dysfunction, Left / Q000175:diagnosis / Q000503:physiopathology* / Q000517:prevention & control*
keywords: Heart rate; QRS duration; Right ventricular apical vs septal pacing