title: Sympathetic reinnervation and heart rate variability after cardiac transplantation.
abstract: BACKGROUND
  Heart rate variability is thought to measure autonomic modulation, but the relation has never been demonstrated directly in humans.
  
  
  OBJECTIVE
  To test the hypothesis that increased low frequency heart rate variability reflects sympathetic reinnervation after cardiac transplantation.
  
  
  METHODS
  24 cardiac transplant recipients at the time of routine surveillance coronary angiography two or more years after cardiac transplantation, and 10 controls with normal coronary arteries undergoing angiography for investigation of chest pain.
  
  
  METHODS
  Regional cardiothoracic centre.
  
  
  METHODS
  Sympathetic effector function at the sinus node was assessed by measuring the fall in cycle length for two minutes after injection of tyramine to the artery supplying the sinus node. Heart rate variability was measured from three-minute RR interval sequences at rest, during metronomic respiration, and before and after atropine.
  
  
  RESULTS
  The logarithm of the low frequency component of heart rate variability during metronomic respiration was linearly related to the logarithm of the change in cycle length after injection of tyramine (R2 = 0.28, P = 0.007). Absolute units more accurately reflected sympathetic effector function than did normalised units or the ratio of low frequency to high frequency. Atropine did not affect high frequency heart rate variability in transplant recipients.
  
  
  CONCLUSIONS
  The low frequency component of heart rate variability is directly related to sympathetic reinnervation to the sinus node.
authors.affiliation: Department of Cardiology, Freeman Hospital, Newcastle upon Tyne, United Kingdom.
authors.forename: S W
authors.initials: SW
authors.lastname: Lord
authors.forename: R H
authors.initials: RH
authors.lastname: Clayton
authors.forename: L
authors.initials: L
authors.lastname: Mitchell
authors.forename: J H
authors.initials: JH
authors.lastname: Dark
authors.forename: A
authors.initials: A
authors.lastname: Murray
authors.forename: J M
authors.initials: JM
authors.lastname: McComb
mesh_terms: D017023:Coronary Angiography; D005260:Female; D006321:Heart / Q000294:innervation*; D006339:Heart Rate / Q000187:drug effects; D016027:Heart Transplantation; D006801:Humans; D008297:Male; D008875:Middle Aged; D009416:Nerve Regeneration; D011184:Postoperative Period; D013564:Sympathetic Nervous System / Q000502:physiology*; D013566:Sympathomimetics; D014439:Tyramine
chemical_list: D013566:Sympathomimetics; D014439:Tyramine