title: Dynamic changes in the QT-R-R relationship during head-up tilt test in patients with vasovagal syncope.
abstract: BACKGROUND
  QT interval is influenced by preceding R-R intervals and autonomic nervous tone. Changes in QT intervals during vasovagal reflex might reflect autonomic modulation of ventricular repolarization; however, this issue has not been fully elucidated. This study aimed to evaluate dynamic response of QT interval to transient changes in R-R interval during vasovagal syncope (VVS) induced by head-up tilt test.
  
  
  METHODS
  Eighteen patients with VVS and 18 age-and sex-matched controls were studied. All patients with VVS had a positive mixed-type response to head-up tilt and all controls had a negative response. CM5-lead digital electrocardiogram (ECG) was recorded and QT intervals were analyzed using Holter ECG analyzer. Using scatter plots of consecutive QT and the preceding R-R intervals, QT-R-R relations during tilt-up and tilt-back or during vasovagal reflex were independently fitted to an exponential curve: QT (second) = A + B x exp[k x R-R (second)].
  
  
  RESULTS
  During the tilt-up, A, B, and k did not differ between patients with VVS and controls. During the tilt back, k showed equivalent positive value compared to the tilt-up (4.1 +/- 1.3 vs -4.6 +/- 0.9) in controls. However, k remained negative (-1.3 +/- 1.5) during vasovagal reflex in patients with VVS. In six patients, in whom metoprolol was effective in eliminating VVS, QT-R-R relationship during the tilt-back became similar to that in controls.
  
  
  CONCLUSIONS
  In patients with VVS, hysteresis of the QT-R-R relation is similarly shown during tilt-up as in controls, whereas this hysteresis is no longer evident and failure of QT prolongation is observed during VVS.
authors.affiliation: Second Department of Internal Medicine, Toyama Medical and Pharmaceutical University, Sugitani, Toyama, Japan. kmizu@ms.toyanna-mpu.ac.jp
authors.forename: Koichi
authors.initials: K
authors.lastname: Mizumaki
authors.forename: Akira
authors.initials: A
authors.lastname: Fujiki
authors.forename: Masao
authors.initials: M
authors.lastname: Sakabe
authors.forename: Kunihiro
authors.initials: K
authors.lastname: Nishida
authors.forename: Masataka
authors.initials: M
authors.lastname: Sugao
authors.forename: Takayuki
authors.initials: T
authors.lastname: Tsuneda
authors.forename: Hidehiko
authors.initials: H
authors.lastname: Nagasawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Inoue
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000494:pharmacology; D000328:Adult; D001341:Autonomic Nervous System / Q000187:drug effects / Q000503:physiopathology*; D016022:Case-Control Studies; D016009:Chi-Square Distribution; D004562:Electrocardiography; D005260:Female; D006339:Heart Rate / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008297:Male; D008790:Metoprolol / Q000494:pharmacology; D019462:Syncope, Vasovagal / Q000503:physiopathology*; D018667:Tilt-Table Test
chemical_list: D000319:Adrenergic beta-Antagonists; D008790:Metoprolol