title: Postexercise recovery of the spatial QRS/T angle as a predictor of sudden cardiac death.
abstract: BACKGROUND
  Postexercise measurement of heart rate (HR) recovery and QT interval dynamics provides prognostic information in various patient populations.
  
  
  OBJECTIVE
  The purpose of this study was to assess whether the measurement of the spatial relationship between the depolarization and repolarization wavefronts (total cosine R-to-T [TCRT]) during the postexercise recovery phase would yield prognostic information.
  
  
  METHODS
  The population consisted of 1297 patients (56 ± 13 years; 67% men) who performed a clinically indicated bicycle stress test. The exercise-recovery hysteresis of TCRT was quantified from the 12-lead exercise electrocardiogram by measuring the TCRT/HR loop area bounded by the exercise and first 3-minute postexercise recovery curves. The HR-corrected TCRT/HR hysteresis was calculated by dividing the area with the HR decrement during the first 3 minutes of recovery. HR recovery was measured at 1 minute postexercise recovery. End points were cardiac death and sudden cardiac death.
  
  
  RESULTS
  During an average follow-up of 45 ± 12 months, 74 patients died (5.7%); 35 (2.6%) were cardiac deaths and 24 (1.9%) were sudden cardiac deaths. Reduced TCRT/HR loop area and TCRT/HR hysteresis were associated with cardiac mortality (P <.001). After adjustments for clinical variables, including ejection fraction, TCRT/HR loop area remained an independent predictor of cardiac death (hazard ratio 5.6; 95% confidence interval 1.6-19.1; P = .007) and sudden cardiac death (10.7; 95% confidence interval 1.4-83.7; P = .024). HR recovery did not remain a significant predictor in the multivariate analysis.
  
  
  CONCLUSIONS
  Attenuated hysteresis of the depolarization and repolarization wavefronts during postexercise recovery is associated with an increased risk of cardiac and sudden cardiac death. Analysis of repolarization dynamics from exercise electrocardiogram represents a promising tool for risk stratification.
authors.affiliation: Division of Cardiology, Institute of Clinical Medicine, University of Oulu, Oulu, Finland. tuomas.kentta@oulu.fi
authors.forename: Tuomas
authors.initials: T
authors.lastname: Kenttä
authors.forename: Jari
authors.initials: J
authors.lastname: Viik
authors.forename: Mari
authors.initials: M
authors.lastname: Karsikas
authors.forename: Tapio
authors.initials: T
authors.lastname: Seppänen
authors.forename: Tuomo
authors.initials: T
authors.lastname: Nieminen
authors.forename: Terho
authors.initials: T
authors.lastname: Lehtimäki
authors.forename: Kjell
authors.initials: K
authors.lastname: Nikus
authors.forename: Rami
authors.initials: R
authors.lastname: Lehtinen
authors.forename: Mika
authors.initials: M
authors.lastname: Kähönen
authors.forename: Heikki V
authors.initials: HV
authors.lastname: Huikuri
mesh_terms: D000328:Adult; D000368:Aged; D016757:Death, Sudden, Cardiac / Q000453:epidemiology*; D005080:Exercise Test; D005260:Female; D006329:Heart Conduction System / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D011379:Prognosis; D018570:Risk Assessment