title: Influence of QRS duration on the prognostic value of T wave alternans.
abstract: BACKGROUND
  T wave alternans (TWA) is a promising new noninvasive marker of arrhythmia vulnerability that quantifies beat-to-beat changes in ventricular repolarization. Secondary repolarization abnormalities are common in subjects with wide QRS complexes. However, the relationship between TWA and QRS prolongation has not been evaluated. The goal of this study was to determine if QRS prolongation influences the prevalence or prognostic value of TWA.
  
  
  RESULTS
  The study consisted of 108 consecutive patients with coronary artery disease and left ventricular ejection fraction < or = 40% who were referred for electrophysiologic studies. Patients underwent TWA testing using bicycle ergometry in the absence of beta-blockers or antiarrhythmic drugs. The primary endpoint was the combined incidence of death, sustained ventricular arrhythmias, and appropriate implantable cardioverter defibrillator therapy. The prognostic value of TWA was assessed in the entire cohort and in two subgroups: QRS < 120 msec (normal, n = 62) and QRS > or = 120 msec (prolonged, n = 46). TWA (hazard ratio 2.2, P = 0.03) and QRS prolongation (hazard ratio 2.2, P = 0.01) were both significant and independent predictors of arrhythmic events. QRS prolongation had no effect on the prevalence of positive TWA tests (QRS < 120 msec: 48%, QRS > or = 120 msec: 50%, P = NS). TWA was a highly significant predictor of events in patients with a normal QRS (hazard ratio 5.8, P = 0.02). In contrast, TWA was not useful for risk stratification in subjects with QRS prolongation (hazard ratio 1.1, P = 0.8).
  
  
  CONCLUSIONS
  TWA is useful only for risk stratification in the absence of QRS prolongation. The presence of QRS prolongation and left ventricular ejection fraction < or = 40% may be sufficient evidence of an adverse prognosis that additional risk stratification is not useful or necessary.
authors.affiliation: Department of Medicine, University of Maryland at Baltimore, Baltimore, Maryland, USA. erashba@medicine.umaryland.edu
authors.forename: Eric J
authors.initials: EJ
authors.lastname: Rashba
authors.forename: Ahmed F
authors.initials: AF
authors.lastname: Osman
authors.forename: Karen
authors.initials: K
authors.lastname: MacMurdy
authors.forename: Malcolm M
authors.initials: MM
authors.lastname: Kirk
authors.forename: Samantha
authors.initials: S
authors.lastname: Sarang
authors.forename: Robert W
authors.initials: RW
authors.lastname: Peters
authors.forename: Stephen R
authors.initials: SR
authors.lastname: Shorofsky
authors.forename: Michael R
authors.initials: MR
authors.lastname: Gold
mesh_terms: D000328:Adult; D000368:Aged; D015331:Cohort Studies; D001026:Coronary Artery Bypass; D003324:Coronary Artery Disease / Q000150:complications / Q000453:epidemiology / Q000601:surgery; D017147:Defibrillators, Implantable; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D023381:Endpoint Determination; D005260:Female; D005500:Follow-Up Studies; D006329:Heart Conduction System / Q000503:physiopathology; D006801:Humans; D008133:Long QT Syndrome / Q000175:diagnosis* / Q000209:etiology; D008297:Male; D008396:Maryland / Q000453:epidemiology; D008875:Middle Aged; D011237:Predictive Value of Tests; D015995:Prevalence; D011379:Prognosis; D012680:Sensitivity and Specificity; D013318:Stroke Volume / Q000502:physiology; D013997:Time Factors; D018487:Ventricular Dysfunction, Left / Q000150:complications / Q000453:epidemiology / Q000601:surgery