title: Effects of autonomic stimulation and blockade on signal-averaged P wave duration.
abstract: OBJECTIVE
  This study sought to evaluate the effects of autonomic stimulation and blockade on the signal-averaged P wave duration.
  
  
  BACKGROUND
  Signal-averaged P wave duration has been shown to have prognostic implications for patients prone to develop atrial fibrillation, but autonomic influences on the signal-averaged P wave duration have not been studied.
  
  
  METHODS
  In 14 healthy volunteers (8 men, 6 women; mean [ +/- SD] age 28.5 +/- 4.8 years, range 22 to 38), signal-averaged P wave duration was measured on day 1 at baseline, during sympathetic stimulation with infusions of epinephrine (50 ng/kg body weight per min) and isoproterenol (50 ng/kg per min), beta-blockade with propranolol (0.2 mg/kg) and autonomic blockade with propranolol followed by atropine (0.04 mg/kg). On a second day, 10 of the 14 subjects returned for repeat baseline recordings and recordings during parasympathetic blockade with atropine (0.04 mg/kg). Signal averaging was performed using a P wave template. Both unfiltered and filtered (least-squares fit filter with 100-ms window) P wave durations were measured. Day to day and interobserver variability were assessed by calculation of intraclass correlation coefficients.
  
  
  RESULTS
  The mean ( +/- SD) baseline filtered P wave duration on day 1 was 141 +/- 10 ms. Isoproterenol infusion significantly shortened the P wave duration to 110 +/- 16 ms (p < 0.001), and epinephrine resulted in significant prolongation to 150 +/- 10 ms (p < 0.05). Beta-adrenergic blockade increased the P wave duration to 153 +/- 10 ms (p < 0.005). Autonomic blockade shortened the P wave duration to 143 +/- 16 ms (p < 0.05 vs. beta-blockade). On the second day, the mean baseline P wave duration was slightly longer (144 +/- 10 ms, p < 0.02). Parasympathetic blockade with atropine resulted in mild shortening of the P wave duration to 136 +/- 15 ms (p < 0.1). Interobserver reproducibility was excellent (intraclass correlation coefficient 0.99). Day to day reproducibility was good (intraclass correlation coefficient 0.56).
  
  
  CONCLUSIONS
  The signal-averaged P wave duration is not a fixed variable because it may change significantly under different autonomic conditions. This has important implications for the application of this test to the heterogeneous population susceptible to atrial fibrillation.
authors.affiliation: Department of Medicine, Northwestern University, Chicago, Illinois, USA.
authors.forename: A N
authors.initials: AN
authors.lastname: Cheema
authors.forename: M W
authors.initials: MW
authors.lastname: Ahmed
authors.forename: A H
authors.initials: AH
authors.lastname: Kadish
authors.forename: J J
authors.initials: JJ
authors.lastname: Goldberger
mesh_terms: D000328:Adult; D001285:Atropine / Q000494:pharmacology; D001341:Autonomic Nervous System / Q000187:drug effects* / Q000502:physiology; D015986:Confounding Factors, Epidemiologic; D004562:Electrocardiography / Q000187:drug effects; D004837:Epinephrine / Q000494:pharmacology; D005260:Female; D006329:Heart Conduction System / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007545:Isoproterenol / Q000494:pharmacology; D008297:Male; D011433:Propranolol / Q000494:pharmacology; D012016:Reference Values; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted
chemical_list: D001285:Atropine; D011433:Propranolol; D007545:Isoproterenol; D004837:Epinephrine