title: Time dependent history improves QT interval estimation in atrial fibrillation.
abstract: OBJECTIVE
  It is not recommended to perform QTc estimation in patients with atrial fibrillation (AF). We evaluated multiple QT interval correction formulas, including a novel time-dependent history approach, in an effort to identify the best method for correcting the QT interval in patients with AF. The ideal correction results in independence between the QTc estimate and HR.
  
  
  METHODS
  Per-beat characteristics were derived using SuperECG (Mortara Instrument). Offline beat-to-beat QTc interval estimates were constructed using standard formulae and averaged (2-10) groups constructed.
  
  
  RESULTS
  Seventy-one patients were included, age 67 ± 10 years, 69% men. Mean-mean QTc intervals varied by correction (range 394-459 ms). Averaging resulted in the same mean-mean QTc estimate, but significantly reduced variability by up to 55%. Time-dependent RR interval history reduced variability the most (Δ 80%), increased QT/RR dynamics (m=.03 vs .17), and was independent with HR (m = 0.0008).
  
  
  CONCLUSIONS
  Our data suggests that QTc interval estimation in patients with AF can be performed reliably using time-dependent history (RRc) outperforming other correction methods.
authors.affiliation: Department of Physiological Nursing, School of Nursing, University of California, San Francisco, San Francisco, CA, USA. david.pickham@ucsf.edu
authors.forename: David
authors.initials: D
authors.lastname: Pickham
authors.forename: David
authors.initials: D
authors.lastname: Mortara
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Drew
mesh_terms: D000368:Aged; D000465:Algorithms; D001281:Atrial Fibrillation / Q000175:diagnosis*; D003936:Diagnosis, Computer-Assisted / Q000379:methods*; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity