title: DeltaT50--a new method to assess temporal ventricular repolarization variability.
abstract: BACKGROUND
  Increased beat-to-beat variability in cardiac repolarization time is a tentative risk marker of drug-induced torsades de pointes. We developed a new, automatic method based on the temporal variability of the T-wave down slope to assess this variability.
  
  
  RESULTS
  Leads V(1) to V(6) of resting electrocardiograms were recorded in 42 healthy subjects (18-68 years, 22 men). The temporal variability at 50% of the T-wave down slope, deltaT50 (1.5 ± 0.41 milliseconds; range, 0.86-2.66 milliseconds), was measured with an accuracy of 1 millisecond on at least 9 pairs of electrocardiogram complexes with a signal-to-noise ratio more than 10 and changes in the R-R interval less than 150 milliseconds. The correlation between repeated measurements of deltaT50 was high. DeltaT50 was measured without corrections for age, sex, heart rate, T-wave amplitude, signal-to-noise ratio, R-R variability, and QTcF because none of these factors explained more than 4% of the within-subject deltaT50 variability.
  
  
  CONCLUSIONS
  The beat-to-beat repolarization variability was measured with high fidelity with the deltaT50 method and was a robust measure in healthy volunteers.
authors.affiliation: AstraZeneca R&D, Mölndal and Sahlgrenska Academy at Sahlgrenska University Hospital, Göteborg, Sweden. christina.abrahamsson@astrazeneca.com
authors.forename: Christina
authors.initials: C
authors.lastname: Abrahamsson
authors.forename: Corina
authors.initials: C
authors.lastname: Dota
authors.forename: Bo
authors.initials: B
authors.lastname: Skallefell
authors.forename: Leif
authors.initials: L
authors.lastname: Carlsson
authors.forename: Dunia
authors.initials: D
authors.lastname: Halawani
authors.forename: Lars
authors.initials: L
authors.lastname: Frison
authors.forename: Anders
authors.initials: A
authors.lastname: Berggren
authors.forename: Nils
authors.initials: N
authors.lastname: Edvardsson
authors.forename: Göran
authors.initials: G
authors.lastname: Duker
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D001145:Arrhythmias, Cardiac / Q000503:physiopathology; D004562:Electrocardiography; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006801:Humans; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D012016:Reference Values; D013997:Time Factors