title: Cardiac repolarization variability in patients with postural tachycardia syndrome during graded head-up tilt.
abstract: OBJECTIVE
  The aim of this study was to assess cardiac ventricular repolarization in patients with postural tachycardia syndrome (POTS) and further the possible link between ventricular repolarization and sympathetic nervous system activity.
  
  
  METHODS
  We recorded body surface ECGs together with plasma noradrenaline (NE) spillover, and muscle sympathetic nerve activity (MSNA) in twelve healthy control subjects (CON; 5 males; age: 23±2 yrs) and 13 subjects with postural tachycardia syndrome (POTS; 4 males; 32±13 yrs) during graded head-up tilt (0°-20°-30°-40°). Ventricular repolarization was assessed by computing various measures of beat-to-beat QT interval variability and T wave amplitude.
  
  
  RESULTS
  In patients with POTS, baseline heart rates were higher and MSNA increases during tilt were more pronounced than in CON. None of the QT variability measures was significantly affected by tilt or different between CON and POTS when corrected for heart rate. Contrary, the T wave amplitude flattened due to tilt (p<0.001) and this effect was significantly more pronounced in POTS (32% at 40°) than in CON (21% at 40°; p=0.03).
  
  
  CONCLUSIONS
  Beat-to-beat variability of the QT interval is normal in patients with POTS. However, significantly more attenuated T waves during head-up tilt together with elevated MSNA levels suggest increased sympathetic outflow to the ventricular myocardium in patients with POTS.
  
  
  CONCLUSIONS
  Monitoring of the T wave during tilt test may provide a non-invasive tool for assessing excessive sympathetic outflow to the ventricular myocardium.
authors.affiliation: Cardiovascular Research Centre, School of Medicine, School of Paediatrics and Reproductive Health, University of Adelaide, Australia. mathias.baumert@adelaide.edu.au
authors.forename: Mathias
authors.initials: M
authors.lastname: Baumert
authors.forename: Elisabeth
authors.initials: E
authors.lastname: Lambert
authors.forename: Gautam
authors.initials: G
authors.lastname: Vaddadi
authors.forename: Carolina Ika
authors.initials: CI
authors.lastname: Sari
authors.forename: Murray
authors.initials: M
authors.lastname: Esler
authors.forename: Gavin
authors.initials: G
authors.lastname: Lambert
authors.forename: Prashanthan
authors.initials: P
authors.lastname: Sanders
authors.forename: Eugene
authors.initials: E
authors.lastname: Nalivaiko
mesh_terms: D000328:Adult; D004562:Electrocardiography / Q000379:methods* / Q000592:standards; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D054972:Postural Orthostatic Tachycardia Syndrome / Q000175:diagnosis* / Q000503:physiopathology*; D018667:Tilt-Table Test / Q000379:methods* / Q000592:standards; D055815:Young Adult