title: Circadian variation of the myocardial ischemic threshold in patients with ischemic heart disease.
abstract: OBJECTIVE
  Circadian variation of the heart rate (HR) at the myocardial ischemic threshold was compared with that of the HR at the sympathetic tone threshold in 16 cases of effort angina pectoris.
  
  
  METHODS
  The high (0.15-0.40 Hz, Hf) and low (0.03-0.15 Hz, Lf) frequency spectral components were extracted every twenty seconds, using frequency domain analysis of the RR interval recorded by a 24-hour Holter ECG with an accelerometer. HR-Hf data collected every five minutes were plotted as the X-Y coordinates, and a two-compartment analysis was performed. The HR at the autonomic tone threshold was then determined at the intersection point of the lines. A loop of the HR-ST segment was drawn during walking to determine the ischemic threshold at which heart rate ischemic ST segment depression began and circadian variation was observed.
  
  
  RESULTS
  The circadian rhythm at the sympathetic tone threshold and the HR at the ischemic threshold were high during the day and low at night. The HR at the ischemic threshold was 15-20% higher than that at the sympathetic tone threshold at night but only 9-13% higher during the day. Also, there was a period during which there was no significant difference between the HR at the two thresholds.
  
  
  CONCLUSIONS
  In comparing circadian variation between HR at the sympathetic tone threshold and HR at the ischemic threshold, there was a period during which there was no significant difference between the HRs. This might suggest a period in which a high incidence of cardiac ischemic attack is likely. This information could provide a feasible indicator for appropriate exercise training for patients with ischemic heart disease.
authors.affiliation: Koujinkai Central Hospital, Sendai, Japan. ino-oka44442@mni.ne.jp
authors.forename: Eiji
authors.initials: E
authors.lastname: Ino-Oka
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Sekino
authors.forename: Yasuaki
authors.initials: Y
authors.lastname: Ohtaki
authors.forename: Hikaru
authors.initials: H
authors.lastname: Inooka
authors.forename: Kouichi
authors.initials: K
authors.lastname: Sagawa
authors.forename: Junichirou
authors.initials: J
authors.lastname: Hashimoto
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Imai
mesh_terms: D000203:Activities of Daily Living; D000368:Aged; D001341:Autonomic Nervous System / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology*; D015716:Electrocardiography, Ambulatory; D015444:Exercise / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology*; D006801:Humans; D008297:Male; D008875:Middle Aged; D017202:Myocardial Ischemia / Q000503:physiopathology*; D013564:Sympathetic Nervous System / Q000502:physiology