title: PR interval: a comparison of electrical and mechanical methods in the fetus.
abstract: BACKGROUND
  Mechanical surrogates are used to assess fetal cardiac electrical activity.
  
  
  OBJECTIVE
  To compare electrical PR interval measured using non-invasive fetal electrocardiography (fECG) with mechanical atrioventricular (AV) interval using Doppler.
  
  
  METHODS
  Prospective study of 55 recordings made in 50 human fetuses. Those with structural heart defects, second degree or complete heart block were excluded.
  
  
  METHODS
  Mechanical AV interval was measured from the onset of mitral A wave to onset of aortic ejection. Electrical PR interval was measured from a coherent averaged signal obtained using non-invasive fECG recorded from the maternal abdomen. Wilcoxon signed rank test was used to compare both methods. Agreement between AV and PR intervals was assessed using linear regression and by Bland-Altman plots. Bland-Altman analysis assessed inter-observer and intra-observer variability.
  
  
  RESULTS
  There was no significant difference in the heart rates of the 55 paired traces measured consecutively using both methods (p<0.35). AV interval was longer than PR (median [range] 116 [96-169] vs. 102 [75-143] ms; p<0.001), with mean difference -16.47 ms (95% Confidence Interval -43.43, 10.44), reflecting the increased proportion of the cardiac cycle measured. Using fECG, PR inter-observer and intra-observer mean differences were 0.4 ms (CI -7.29, 8.09) and 0.7 ms (CI -3.22, 4.62) respectively. R values for inter and intra-observer studies were 0.95 and 0.99 respectively. Using Doppler methods, AV inter-observer and intra-observer mean differences were -2.69 ms, (CI -15.33, 9.95) and 0.92 ms, (CI -9.41, 11.26) respectively. R values for AV measurements were 0.93 for inter-observer and 0.96 for intra-observer variation.
  
  
  CONCLUSIONS
  Non-invasive fECG is a robust tool to measure the PR interval with narrow limits of agreement.
authors.affiliation: Institute of Reproductive and Developmental Biology, Faculty of Medicine, Imperial College at Queen Charlotte's and Chelsea Hospital, London, UK.
authors.forename: Lucia
authors.initials: L
authors.lastname: Pasquini
authors.forename: Anna N
authors.initials: AN
authors.lastname: Seale
authors.forename: Cristian
authors.initials: C
authors.lastname: Belmar
authors.forename: Salome
authors.initials: S
authors.lastname: Oseku-Afful
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Thomas
authors.forename: Myles J O
authors.initials: MJ
authors.lastname: Taylor
authors.forename: Michael
authors.initials: M
authors.lastname: Roughton
authors.forename: Helena M
authors.initials: HM
authors.lastname: Gardiner
mesh_terms: D000328:Adult; D015148:Cardiotocography / Q000379:methods*; D004562:Electrocardiography; D005260:Female; D005333:Fetus / Q000502:physiology*; D006340:Heart Rate, Fetal; D006801:Humans; D011247:Pregnancy