Circadian variation of the myocardial ischemic threshold in patients with ischemic heart disease.
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.
Ino-Oka
Eiji
E
Koujinkai Central Hospital, Sendai, Japan. ino-oka44442@mni.ne.jp
Sekino
Hiroshi
H
Ohtaki
Yasuaki
Y
Inooka
Hikaru
H
Sagawa
Kouichi
K
Hashimoto
Junichirou
J
Imai
Yutaka
Y
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