title: Rate-dependent measures of repolarization predict inducibility of ventricular arrhythmias.
abstract: OBJECTIVE
  The aim of this study was to compare the rate-dependent measures of repolarization in patients with and without inducible ventricular arrhythmias, and so to assess the potential arrhythmogenic role of rate-dependent heterogeneities in cardiac repolarization.
  
  
  METHODS
  Two groups of patients were studied during invasive electrophysiological procedures for standard clinical indications. A normal group (n = 17) with supraventricular tachycardia, structurally normal hearts and no inducible ventricular arrhythmias (PES-) and an inducible group (n = 13) with inducible ventricular arrhythmias (PES+). In each patient, we delivered a series of S1-S2 pacing sequences with a baseline S2 of 500 ms, which was progressively reduced. At the same time, a 12-lead electrocardiogram (ECG) was recorded. T-waves were extracted from each ECG recording, and 12 different T-wave measures were obtained from each patient across a range of coupling intervals. These included conventional measures, and those obtained from principal component analysis (PCA) of repolarization waveforms.
  
  
  RESULTS
  At baseline S2, there was no significant difference between the PES- and PES+ using conventional T-wave measures. There were significant differences at baseline S2 between groups using PCA-derived measures. These differences showed rate dependence and were larger at shorter coupling intervals. Two dynamic ECG measurements identified subjects who were inducible during PES; maximum relative T-wave residuum >0.10 (odds ratio: 38.5, 95% CI: 4.7-318.5; P < 0.001) and maximum T-wave shape index <0.007 (odds ratio: 180.0, 95% CI: 10.2-3167.0; P < 0.001).
  
  
  CONCLUSIONS
  T-wave shape index is rate dependent and discriminates between PES- and PES+ patients. We propose that patients with inducible arrhythmias have rate-dependent heterogeneity of repolarization which could be a useful tool for risk stratification.
authors.affiliation: South Yorkshire Cardiac Centre, Northern General Hospital, Herries Road, Sheffield S57AU, UK. p.j.sheridan@sheffield.ac.uk
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Sheridan
authors.forename: Jefferson L B
authors.initials: JL
authors.lastname: Marques
authors.forename: Christopher M H
authors.initials: CM
authors.lastname: Newman
authors.forename: Simon R
authors.initials: SR
authors.lastname: Heller
authors.forename: Richard H
authors.initials: RH
authors.lastname: Clayton
mesh_terms: D000200:Action Potentials / Q000502:physiology*; D000328:Adult; D000368:Aged; D002304:Cardiac Pacing, Artificial; D003971:Diastole / Q000502:physiology; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac / Q000592:standards*; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008955:Models, Cardiovascular; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D012307:Risk Factors; D013617:Tachycardia, Supraventricular / Q000175:diagnosis / Q000453:epidemiology / Q000503:physiopathology; D017180:Tachycardia, Ventricular / Q000175:diagnosis* / Q000453:epidemiology / Q000503:physiopathology*