title: The positive T wave.
abstract: OBJECTIVE
  The instant of maximum slope (Tup) of the T wave in the unipolar electrogram is a well-established measure of repolarisation time (TR). Nevertheless, recent observations on positive T waves have caused a renewed debate. The purpose of this study was to elucidate the mechanism that leads to positive and negative T waves and to investigate which electrogram feature best predicts TR.
  
  
  METHODS
  We simulated propagating action potentials (AP) and electrograms with a bidomain reaction-diffusion model of the human heart including heterogeneous ion-channel properties. To explain positive T waves we compared results with those of a much simpler model, which predicts T waves from local and remote AP.
  
  
  RESULTS
  Repolarisation time was defined as the instant of steepest downstroke of the AP. T wave polarity was mostly determined by TR. Positive T waves occurred at early-repolarising sites. Correlation between Tup and TR was >0.99, in both negative and positive T waves. T wave area and peak value also correlated highly with TR.
  
  
  CONCLUSIONS
  The polarity of the T wave is primarily determined by TR. Positive T waves occur at early-repolarising sites. Local TR is best estimated by Tup, also in positive T waves.
authors.affiliation: Department of Physiology, Institute of Biomedical Engineering, Université de Montréal, Montréal, Québec, Canada. mark@potse.nl
authors.forename: Mark
authors.initials: M
authors.lastname: Potse
authors.forename: Ruben
authors.initials: R
authors.lastname: Coronel
authors.forename: Tobias
authors.initials: T
authors.lastname: Opthof
authors.forename: Alain
authors.initials: A
authors.lastname: Vinet
mesh_terms: D000200:Action Potentials; D001145:Arrhythmias, Cardiac / Q000503:physiopathology*; D003198:Computer Simulation; D004562:Electrocardiography; D006801:Humans