title: QT restitution properties of middle-aged women with different exercise capacities.
abstract: BACKGROUND
  Framingham Study data indicate an incremental risk of cardiovascular death in relation to low exercise capacity in women. The reason for death is still not clear.
  
  
  METHODS
  QT restitution properties in 80 middle-aged women were investigated to confirm whether the cardiac restitution property was affected by the exercise capacity. Exercise tests were performed according to the Bruce protocol. Seventy cases were divided into the low-exercise capacity group (LEC group) and high-exercise capacity group (HEC group) by median exercise capacities. Sequential QT intervals and their preceding TQ intervals were measured, and the QT restitution curve (QTRC) was constructed. Two exponential equations were used to match the data and calculate the maximum slope (Smax) of QTRC, respectively.
  
  
  RESULTS
  With elevation in the exercise level, the women in the LEC group had a higher change rate of QT intervals (41 ± 10 vs 29 ± 3 ms/Met, P = .001) and TQ intervals (46 ± 12 vs 41 ± 7 ms/Met, P = .046); and the ratio of QT interval alterations to TQ interval alterations increased (0.41 ± 0.09 vs 0.36 ± 0.07, P = .003). The Smax of the QTRC in the LEC group was higher than that in the HEC group (1.43 ± 0.44 vs 1.13 ± 0.34, P = .002). There was an inverse relationship between Smax and exercise capacity (r = -0.43, P = .001).
  
  
  CONCLUSIONS
  Middle-aged women with low exercise capacity have steeper QTRCs than those with high exercise capacity, denoting a more unstable alternation of QT interval with elevation in exercise level.
authors: Department of Cardiology, The Tenth People's Hospital of Tongji University, Shanghai, China.
authors: Dongdong
authors: D
authors: Zhao
authors: Yong
authors: Y
authors: Wang
authors: Yidong
authors: Y
authors: Wei
authors: Kai
authors: K
authors: Tang
authors: XueJing
authors: X
authors: Yu
authors: Yawei
authors: Y
authors: Xu
mesh_terms: D002318:Cardiovascular Diseases / Q000175:diagnosis / Q000503:physiopathology; D004562:Electrocardiography / Q000379:methods*; D005080:Exercise Test; D017079:Exercise Tolerance / Q000502:physiology*; D005260:Female; D006329:Heart Conduction System / Q000502:physiology*; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D008875:Middle Aged; D011379:Prognosis; D018570:Risk Assessment; D012307:Risk Factors; D018709:Statistics, Nonparametric