title: Beat-to-beat determinants of the beat-to-beat temporal and spatial variability of repolarization.
abstract: The goal of this study was to compare the time series predictors of beat-to-beat variability in repolarization in healthy individuals.
  
  
  
  Spatial QRS- and T-vector amplitudes, spatial QRS-T, RR' and TT' angles, RR' and QT intervals, and QRS- and T-loop roundness were measured on 453 consecutive sinus beats in 168 healthy subjects (mean age 39.8±15.6years; 50% men; 93% white). Panel time-series regression models were adjusted by age, sex, and race. Appropriate time series of ECG metrics served as predictors and outcomes.
  
  
  
  Increase in T-loop roundness index by 0.1 was associated with 1.1° (95%CI 0.9-2.2; P=0.048) increase in corresponding TT' angle. One unit increase in a respiration index was associated with 4ms (95%CI 0.6-7.0; P=0.021) increase in QT interval.
  
  
  
  Spatial TT' angle and beat-to-beat variability in T-loop roundness represent intrinsic measures of repolarization variability. QT interval variability characterizes the effect of respiration and heart rate variability.
authors.affiliation: Whiting School of Engineering, Johns Hopkins University, Baltimore, MD, USA.
authors.forename: Albert
authors.initials: A
authors.lastname: Feeny
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; D000465:Algorithms; D003198:Computer Simulation; D003936:Diagnosis, Computer-Assisted / Q000379:methods; D004562:Electrocardiography / Q000379:methods*; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology*; D000070276:Heart Rate Determination / Q000379:methods*; D006801:Humans; D008297:Male; D008955:Models, Cardiovascular; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014672:Vectorcardiography / Q000379:methods*
keywords: QT interval; Repolarization; Repolarization variability; Spatial TT′ angle