title: Can cardiac vagal tone be estimated from the 10-second ECG?
abstract: BACKGROUND
  Heart rate variability (HRV) recorded over 5 min or 24 h is used increasingly to measure autonomic function and as a prognostic indicator in cardiology. Measuring HRV during a standard 10-s ECG would save time and cut costs. The aim of this study, therefore, was to discover whether indices of HRV calculated over 10 s could predict cardiac vagal tone (CVT) recorded over a 5-min period by the NeuroScope, a new instrument that selectively measures vagal tone.
  
  
  METHODS
  A total of 50 subjects had ECGs taken at the beginning, middle and end of a 5-min measurement of CVT. Standard deviation of normal-to-normal RR interval (SDNN), root mean square of successive differences in RR intervals (rMSSD), and the average absolute difference (AAD) in RR intervals were calculated from RR intervals derived from the ECGs. Subjects were divided into a training set (n=40) and a test set (n=10).
  
  
  RESULTS
  Regression equations derived from the training set predicted 5-min mean CVT in the test set with r(2) of 95.8%, 92.9% and 87.9% for AAD, rMSSD and SDNN, respectively. Indices obtained from the third ECG in each set tended to give a closer relationship with CVT than those derived from the first and second ECGs: this could be because of the greater spread of the independent variables in the third set. An underlying linear physiological phenomenon could not be excluded, however, without continuing the measurements over a longer time.
  
  
  CONCLUSIONS
  These results demonstrate that AAD and rMSSD calculated from a 10-s ECG can accurately predict 5-min mean CVT as measured by the NeuroScope.
authors.affiliation: University Section of Cardiology and Exercise Medicine, Queen Elizabeth Building, Glasgow Royal Infirmary, 10 Alexandra Parade, Glasgow G31 2ER, UK.
authors.forename: Ruth M
authors.initials: RM
authors.lastname: Hamilton
authors.forename: Peter S
authors.initials: PS
authors.lastname: McKechnie
authors.forename: Peter W
authors.initials: PW
authors.lastname: Macfarlane
mesh_terms: D000328:Adult; D000368:Aged; D004562:Electrocardiography; D022062:Electrophysiologic Techniques, Cardiac; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D010275:Parasympathetic Nervous System / Q000502:physiology; D011237:Predictive Value of Tests; D013223:Statistics as Topic; D006113:United Kingdom / Q000453:epidemiology