title: Repolarization lability measured on 10-second ECG by spatial TT' angle: reproducibility and agreement with QT variability.
abstract: BACKGROUND
  Reproducibility of spatial TT' angle on the 10-second ECG and its agreement with QT variability has not been previously studied.
  
  
  METHODS
  We analyzed 2 randomly selected 10-second segments within 3-minute resting orthogonal ECG in 172 healthy IDEAL study participants (age 38.1±15.2years, 50% male, 94% white). Repolarization lability was measured by the QT variance (QTV), short-term QT variability (STV(QT)), and spatial TT' angle. Bland-Altman analysis was used to assess the agreement between different log-transformed metrics of repolarization lability, and to assess the reproducibility.
  
  
  RESULTS
  The heart rate showed a very high reproducibility (bias 0.14%, Lin's rho_c=0.99). As expected, noise suppression by averaging improves reproducibility. Agreement between two 10-second LogQTV was poor (bias -0.04; 95% limits of agreement [-1.89; 1.81]), while LogSTV(QT) (0.04 [-1.01; 1.10]), and especially LogTT' angle (-0.009 [-0.84; 0.82]) was better.
  
  
  CONCLUSIONS
  TT' angle is a satisfactory reproducible metric of repolarization lability on the 10-second ECG.
authors.affiliation: Whiting School of Engineering, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: Feeny
authors.affiliation: Whiting School of Engineering, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Lichy
authors.initials: L
authors.lastname: Han
authors.affiliation: The Division of Cardiology, Department of Medicine, Johns Hopkins Hospital, Baltimore, MD, USA; The Knight Cardiovascular Institute, Oregon Health & Science University, Portland, OR, USA. Electronic address: tereshch@ohsu.edu.
authors.forename: Larisa G
authors.initials: LG
authors.lastname: Tereshchenko
mesh_terms: D000328:Adult; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D015203:Reproducibility of Results
keywords: ECG; Repolarization; Spatial TT′ angle