title: Corrected QT in ventricular paced rhythms: what is the validation for commonly practiced assumptions?
abstract: BACKGROUND
  Ventricular pacing (VP) may impact the accuracy of QT interval measurement, as it increases the QT by increasing the QRS duration amongst other mechanisms. We aimed to investigate the accuracy of the commonly used clinical practice of subtracting 50 ms from the corrected QT (QTc) in ventricular paced rhythms.
  
  
  METHODS
  We conducted a prospective observational study on 23 consecutive pacemaker patients. Four ECGs were recorded for each subject, 2 in their native rate and 2 following an atrial paced, atrial sensed and inhibited response to sensing and then a dual pacing, dual sensing and dual response pacing of 100 bpm to allow for an intrinsic and a ventricular paced QRS, respectively. The averaged QTc in the ventricular paced rhythm was then compared with the non-ventricular-paced QTc for individual subjects.
  
  
  RESULTS
  At a mean spontaneous heart rate of 66 bpm (SD ±8), the mean difference in QTc between the ventricular paced and nonpaced QRS was 48.27 ms (95% CI = 32-64.6 ms, p < 0.001). At faster paced rates, the mean QTc difference was 81.3 ms (95% CI = 35.8-126.8 ms, p = 0.002).
  
  
  CONCLUSIONS
  The QTc measurement during VP confirms the current 50-ms subtraction assumption rule within a range of ±16 ms at an average heart rate of 66 bpm. However, at faster heart rates, the 50-ms adjustment may underestimate the QTc discrepancy between a wide and normal QRS.
authors: Department of Cardiovascular Medicine, Hartford Hospital, Hartford, Conn., USA.
authors: Saneka
authors: S
authors: Chakravarty
authors: Jeffrey
authors: J
authors: Kluger
authors: Lovely
authors: L
authors: Chhabra
authors: Bhavadharini
authors: B
authors: Ramu
authors: Craig
authors: C
authors: Coleman
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D002304:Cardiac Pacing, Artificial / Q000379:methods*; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006352:Heart Ventricles / Q000503:physiopathology*; D006801:Humans; D008297:Male; D011446:Prospective Studies; D013610:Tachycardia / Q000628:therapy*