title: Beat-to-beat three-dimensional ECG variability predicts ventricular arrhythmia in ICD recipients.
abstract: BACKGROUND
  Methodological difficulties associated with QT measurements prompt the search for new electrocardiographic markers of repolarization heterogeneity.
  
  
  OBJECTIVE
  We hypothesized that beat-to-beat 3-dimensional vectorcardiogram variability predicts ventricular arrhythmia (VA) in patients with structural heart disease, left ventricular systolic dysfunction, and implanted implantable cardioverter-defibrillators (ICDs).
  
  
  METHODS
  Baseline orthogonal electrocardiograms were recorded in 414 patients with structural heart disease (mean age 59.4 ± 12.0; 280 white [68%] and 134 black [32%]) at rest before implantation of ICD for primary prevention of sudden cardiac death. R and T peaks of 30 consecutive sinus beats were plotted in 3 dimensions to form an R peaks cloud and a T peaks cloud. The volume of the peaks cloud was calculated as the volume within the convex hull. Patients were followed up for at least 6 months; sustained VA with appropriate ICD therapies served as an end point.
  
  
  RESULTS
  During a mean follow-up time of 18.4 ± 12.5 months, 61 of the 414 patients (14.73% or 9.6% per person-year of follow-up) experienced sustained VA with appropriate ICD therapies: 41 of them were white and 20 were black. In the multivariate Cox model that included inducibility of VA and use of beta-blockers, the highest tertile of T/R peaks cloud volume ratio significantly predicted VA (hazard ratio 1.68, 95% confidence interval 1.01 to 2.80; P = .046) in all patients. T peaks cloud volume and T/R peaks cloud volume ratio were significantly smaller in black subjects (median 0.09 [interquartile range 0.04 to 0.15] vs. median 0.11 [interquartile range 0.06 to 0.22], P = .002).
  
  
  CONCLUSIONS
  A relatively large T peaks cloud volume is associated with increased risk of VA in patients with structural heart disease and systolic dysfunction.
authors.affiliation: Division of Cardiology, Department of Medicine, Johns Hopkins Hospital, Baltimore, Maryland, USA. lteresh1@jhmi.edu
authors.forename: Larisa G
authors.initials: LG
authors.lastname: Tereshchenko
authors.forename: Lichy
authors.initials: L
authors.lastname: Han
authors.forename: Alan
authors.initials: A
authors.lastname: Cheng
authors.forename: Joseph E
authors.initials: JE
authors.lastname: Marine
authors.forename: David D
authors.initials: DD
authors.lastname: Spragg
authors.forename: Sunil
authors.initials: S
authors.lastname: Sinha
authors.forename: Darshan
authors.initials: D
authors.lastname: Dalal
authors.forename: Hugh
authors.initials: H
authors.lastname: Calkins
authors.forename: Gordon F
authors.initials: GF
authors.lastname: Tomaselli
authors.forename: Ronald D
authors.initials: RD
authors.lastname: Berger
mesh_terms: D000368:Aged; D001145:Arrhythmias, Cardiac / Q000175:diagnosis*; D017147:Defibrillators, Implantable; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D014672:Vectorcardiography
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