title: Optimal target heart rate for exercise-induced T-wave alternans.
abstract: OBJECTIVE
  This study was conducted to determine the optimal target heart rate (HR) for the use of exercise-induced T-wave alternans (TWA) as an index for risk of malignant ventricular tachyarrhythmias.
  
  
  BACKGROUND
  Rate-dependent TWA is an index of vulnerability to ventricular tachyarrhythmias. However, false positive TWA was reported to occur in normal subjects at high HR.
  
  
  METHODS
  Two groups were evaluated: Group I: 50 patients with malignant ventricular tachyarrhythmias, who received an implantable cardioverter-defibrillator (ICD); and Group II: 55 age-matched normal subjects. In both Groups, TWA was evaluated during symptom-limited bicycle exercise test.
  
  
  RESULTS
  Peak HR during exercise test was 103 +/- 17 beats/min in Group I, versus 124 +/- 18 beats/min in Group II (P < 0.001). In Group I, 4 patients were excluded from analysis, due to high noise level or frequent ectopy during exercise. Out of the remaining 46 patients, TWA was present in 28 patients (61%), and absent in 18 (39%). In group II, TWA was present in four subjects (7%), and absent in 51 (93%). HR at the onset of TWA was 91 +/- 11/min in Group I, and 119 +/- 12/min in Group II (P < 0.001). Receiver operated characteristics curves demonstrated that a HR of 115 beats/min was the cutoff with the best sensitivity and specificity for TWA (100 and 96%, respectively). None of the patients in Group I developed TWA at HR > 115 beats/min, while two out of four in Group II had TWA at HR > 115/minutes. However, 13 patients in Group I who had no TWA were unable to exercise to a peak HR > 115 beats/min, compared to nine subjects in Group II.
  
  
  CONCLUSIONS
  A target HR of 115 beats/min was highly sensitive and specific for determination of exercise-induced TWA as an index of risk of malignant ventricular tachyarrhythmias. However, a significant number of patients may not be able to achieve this target HR, resulting in an indeterminate test. The value of pharmacologic testing in this group should be assessed.
authors.affiliation: Department of Medicine, State University of New York -- Downstate Medical Center and Veterans Affairs Medical Center, Brooklyn, NY 11203, USA. gturitto@aol.com
authors.forename: G
authors.initials: G
authors.lastname: Turitto
authors.forename: E B
authors.initials: EB
authors.lastname: Caref
authors.forename: G
authors.initials: G
authors.lastname: El-Attar
authors.forename: M
authors.initials: M
authors.lastname: Helal
authors.forename: A
authors.initials: A
authors.lastname: Mohamed
authors.forename: R P
authors.initials: RP
authors.lastname: Pedalino
authors.forename: N
authors.initials: N
authors.lastname: El-Sherif
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016022:Case-Control Studies; D017147:Defibrillators, Implantable; D004562:Electrocardiography / Q000379:methods* / Q000592:standards; D005080:Exercise Test / Q000379:methods* / Q000592:standards; D005189:False Positive Reactions; D005260:Female; D006339:Heart Rate; D006801:Humans; D008297:Male; D008875:Middle Aged; D012307:Risk Factors; D012680:Sensitivity and Specificity; D017180:Tachycardia, Ventricular / Q000175:diagnosis* / Q000209:etiology* / Q000628:therapy