Y. Goseki et al., HEART-RATE-VARIABILITY BEFORE THE OCCURRENCE OF SILENT-MYOCARDIAL-ISCHEMIA DURING AMBULATORY MONITORING, The American journal of cardiology, 73(12), 1994, pp. 845-849
Thirty-three ischemic episodes in 19 patients with stable coronary art
ery disease were studied to clarify changing autonomic nervous system
activity during daily life before the occurrence of myocardial ischemi
a. Nonischemic points were studied for comparison of control data with
ischemic episodes. These were defined as (1) patient showing no ische
mic ST-T change while having the same heart rate with onset of ischemi
c episodes, and (2) presence within 1 to 2 hours before or after onset
of ischemic episodes in the same patient. We analyzed heart rate (HR)
variability during the 30 minute period before the onset and after th
e end of ischemic episodes during 24-hour monitoring. The period of 30
to 40 minutes before Ischemia was regarded as the baseline, and HR va
riability was analyzed at 10-minute intervals before each ischemic epi
sode and nonischemic point. HR variability was quantified on the band
of 2 components: low frequency (0.04 to 0.15 Hz; 19) and high frequenc
y (0.15 to 0.40 Hz; HF). Of the 33 episodes, 24 (73%) had a greater LF
/HF value during the 30-minute period before ischemia than that before
the nonischemic points. Distribution of the number of the 24 episodes
demonstrated circadian rhythm with a peak from 8 to 10 A.M. HF power
began to decrease from the last 10 minutes before ischemia, compared w
ith baseline. A significant decrease in HF power with a background of
greater value of LF/HF may explain the reduced ischemic threshold for
ischemia during daily life.