title: Differential autonomic mechanisms underlying early morning and daytime transient myocardial ischaemia in patients with stable coronary artery disease.
abstract: OBJECTIVE
  To see whether autonomic regulatory mechanisms play a part in transient myocardial ischaemia in patients treated with beta blockers.
  
  
  METHODS
  Prospective study.
  
  
  METHODS
  Outpatients' clinic.
  
  
  METHODS
  51 consecutive patients with angiographically documented coronary artery disease, stable angina, and transient myocardial ischaemia despite beta blockade.
  
  
  METHODS
  24 hour ambulatory electrocardiographic monitoring for analysis of variability in ST depression and heart rate.
  
  
  METHODS
  Numbers of episodes of ischaemia, with an ST depression of > or = 0.1 mV 80 ms after the J point that lasted > or = 60 s at an interval of > or = 60 s from a previous ischaemic episode. Heart rate at onset of ischaemia. Normalised spectral analysis of heart rate variability; ratio of low to high frequency power to assess the sympathovagal balance.
  
  
  RESULTS
  Despite treatment, 258 episodes of transient ischaemia were recorded. At heart rates at onset of ischaemia of < 70 beats per minute a high ratio of low to high frequency power accompanied the ischaemic events and was paralleled by a remarkably reduced high frequency power. The high ratio--that is, enhanced sympathetic tone during ischaemia--was mainly found in the early morning. By contrast, ischaemic episodes with heart rates at onset of > or = 70 beats per minute were not associated with significant changes in the parameters of autonomic function.
  
  
  CONCLUSIONS
  During beta blockade the residual transient ischaemia is associated with decreased variability in heart rate. In particular, in ischaemic episodes with a low heart rate at onset the neural regulation of the heart plays a part. Apparently, variability in heart rate is not sufficiently modified by beta blockers to prevent all ischaemia. The ischaemia related change in the autonomic nervous system during the early morning is in agreement with previous studies, showing increased cardiovascular risk at this time of the day.
authors.affiliation: Department of Cardiology, University Hospital, Groningen, The Netherlands.
authors.forename: A J
authors.initials: AJ
authors.lastname: van Boven
authors.forename: J
authors.initials: J
authors.lastname: Brouwer
authors.forename: H J
authors.initials: HJ
authors.lastname: Crijns
authors.forename: J
authors.initials: J
authors.lastname: Haaksma
authors.forename: K I
authors.initials: KI
authors.lastname: Lie
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000627:therapeutic use; D000787:Angina Pectoris / Q000188:drug therapy / Q000503:physiopathology; D001341:Autonomic Nervous System / Q000503:physiopathology*; D002940:Circadian Rhythm; D015716:Electrocardiography, Ambulatory; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000503:physiopathology*; D011446:Prospective Studies
chemical_list: D000319:Adrenergic beta-Antagonists