title: Intracardiac QT integral on far-field ICD electrogram predicts sustained ventricular tachyarrhythmias in ICD patients.
abstract: BACKGROUND
  Prediction of sustained ventricular tachycardia (VT)/ventricular fibrillation (VF) could help to guide preventive interventions in at-risk patients. The QRST integral (∫QT) reflects intrinsic repolarization properties.
  
  
  OBJECTIVE
  The objective of this study was to determine whether intracardiac ∫QT predicts VT/VF in the next few months in patients with implantable cardioverter defibrillators (ICDs).
  
  
  METHODS
  Far-field (FF) and near-field (NF) right ventricular intracardiac electrograms (EGMs) were recorded via telemetry in 46 patients with structural heart disease and ICDs implanted for secondary prevention of sudden cardiac death. Epochs of 4.9 ± 0.4 minutes during sinus rhythm (mean heart rate 70.9 ± 15.2 beats/min) and ventricular pacing at 105 beats/min were analyzed. Mean ∫QT was calculated on FF and NF EGMs as the algebraic sum of areas under the QRST curve and adjusted by mean heart rate. Patients were followed up for at least 3 months. True VT/VF events treated by the ICD served as the end point.
  
  
  RESULTS
  During a mean follow-up of 4.6 months, 22 patients (48%) were treated for VT/VF. Unadjusted and adjusted by heart rate, FF EGM ∫QT in sinus rhythm was a significant predictor of VT/VF (unadjusted ∫QT hazard ratio 1.007; 95% confidence interval 1.002 to 1.0013; P = .007; adjusted ∫QT hazard ratio 1.68; 95% confidence interval 1.19 to 2.36; P = .002). The highest quartile of intracardiac ∫QT predicted VT/VF (log-rank test P = .042) and identified patients at risk with a specificity of 86% and positive predictive value of 73%.
  
  
  CONCLUSIONS
  Increased intracardiac FF EGM ∫QT predicts VT/VF in patients with structural heart disease and secondary prevention ICDs.
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: Raja N
authors.initials: RN
authors.lastname: Ghanem
authors.forename: Athula
authors.initials: A
authors.lastname: Abeyratne
authors.forename: Charles D
authors.initials: CD
authors.lastname: Swerdlow
mesh_terms: D000368:Aged; D017147:Defibrillators, Implantable; D004562:Electrocardiography; D015716:Electrocardiography, Ambulatory; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D016016:Proportional Hazards Models; D011446:Prospective Studies; D012680:Sensitivity and Specificity; D017180:Tachycardia, Ventricular / Q000503:physiopathology* / Q000628:therapy*; D013686:Telemetry