title: Exercise-induced QT/R-R-interval hysteresis as a predictor of myocardial ischemia.
abstract: OBJECTIVE
  Exercise-induced QT/RR hysteresis exists when, for a given R-R interval, the QT interval duration is shorter during recovery after exercise than during exercise. We sought to assess the association between QT/RR hysteresis and imaging evidence of myocardial ischemia.
  
  
  BACKGROUND
  Because ischemia induces cellular disturbances known to decrease membrane action potential duration, we hypothesized a correlation between QT/RR and myocardial ischemia.
  
  
  METHODS
  We digitally analyzed 4-second samples of QT duration and R-R-interval duration in 260 patients referred for treadmill exercise stress and rest single photon emission computed tomography myocardial perfusion imaging; a cool-down period was used after exercise. None of the patients were in atrial fibrillation or used digoxin, and none had marked baseline electrocardiographic abnormalities. Stress and rest myocardial perfusion images were analyzed visually and quantitatively to define the extent and severity of stress-induced ischemia. QT/RR hysteresis was calculated using a computerized algorithm.
  
  
  RESULTS
  There were 82 patients (32%) who manifested myocardial ischemia by single photon emission computed tomography myocardial perfusion imaging. The likelihood of ischemia increased with increasing QT/RR hysteresis, with prevalence according to quartiles of 20%, 30%, 26%, and 49% (P = .003 for trend). In analyses adjusting for ST-segment changes, exercise capacity, heart rate recovery, and other confounders, QT/RR hysteresis was independently predictive of presence of myocardial ischemia (adjusted odds ratio for 100-point increase of QT/RR hysteresis, 1.61; 95% confidence interval, 1.22-2.12; P = .0008). QT/RR hysteresis was also predictive of severe ischemia.
  
  
  CONCLUSIONS
  Exercise-induced QT/RR hysteresis is a strong and independent predictor of myocardial ischemia and provides additional information beyond that afforded by standard ST-segment measures.
authors.affiliation: Department of Cardiovascular Medicine, Cleveland Clinic Foundation, OH 44195, USA. lauerm@ccf.org
authors.forename: Michael S
authors.initials: MS
authors.lastname: Lauer
authors.forename: Claire E
authors.initials: CE
authors.lastname: Pothier
authors.forename: Yuri B
authors.initials: YB
authors.lastname: Chernyak
authors.forename: Richard
authors.initials: R
authors.lastname: Brunken
authors.forename: Michael
authors.initials: M
authors.lastname: Lieber
authors.forename: Carolyn
authors.initials: C
authors.lastname: Apperson-Hansen
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Starobin
mesh_terms: D000368:Aged; D004562:Electrocardiography / Q000379:methods* / Q000706:statistics & numerical data*; D005080:Exercise Test / Q000379:methods* / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D017202:Myocardial Ischemia / Q000175:diagnosis* / Q000453:epidemiology*; D015995:Prevalence; D011379:Prognosis; D015203:Reproducibility of Results; D018570:Risk Assessment / Q000379:methods*; D012307:Risk Factors; D012680:Sensitivity and Specificity