title: Effect of heart rate on QT interval in children and adolescents.
abstract: OBJECTIVE
  To study the effect of sympathetic stimulation and increase in heart rate on the QT and QTc intervals.
  
  
  METHODS
  Prospective non-randomised study of eight consecutive patients.
  
  
  METHODS
  Electrophysiology laboratory at a tertiary centre.
  
  
  METHODS
  Eight patients aged 10-20 years (median 12.5) undergoing repeat electrophysiological study after previously successful catheter ablation (n = 6) or presumed supraventricular tachycardia (n = 2) with negative studies.
  
  
  METHODS
  Electrocardiograms were obtained (a) at baseline, (b) during atrial pacing at 450 ms cycle length, (c) during isoprenaline infusion at 0.025 microgram/kg/min, (d) adding atrial pacing (450 ms cycle length) to isoprenaline at 0.025 microgram/kg/min, and (e) isoprenaline at 0.05 microgram/kg/min.
  
  
  METHODS
  QT and QTc intervals at each of the above mentioned stages.
  
  
  RESULTS
  The QT interval was reduced from a mean value of 350 ms to around 315-325 ms by each of the above manoeuvres. Correspondingly, the QTc increased from a mean of 407 ms to around 445-470 ms. Pacing was as effective as isoprenaline in shortening the QT interval and prolonging the QTc intervals.
  
  
  CONCLUSIONS
  Heart rate directly influences QT and QTc intervals in children and adolescents. The QT is shortened, but QTc is prolonged. Hence, reliance on the QTc alone could lead to mistaken diagnosis of long QT syndrome.
authors.affiliation: South Carolina Children's Heart Center, Medical University of South Carolina, Charleston 29425, USA.
authors.forename: S
authors.initials: S
authors.lastname: Balaji
authors.forename: Y R
authors.initials: YR
authors.lastname: Lau
authors.forename: P C
authors.initials: PC
authors.lastname: Gillette
mesh_terms: D000293:Adolescent; D000328:Adult; D002304:Cardiac Pacing, Artificial; D002316:Cardiotonic Agents; D002648:Child; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate; D006801:Humans; D007545:Isoproterenol; D008133:Long QT Syndrome / Q000175:diagnosis; D008297:Male; D011446:Prospective Studies; D013617:Tachycardia, Supraventricular / Q000503:physiopathology*
chemical_list: D002316:Cardiotonic Agents; D007545:Isoproterenol