The autonomic nervous control of the cardiovascular system has been thought to have a diurnal variation in its activity. This variation could be an important underlying mechanism for the circardian distribution of cardiac events such as angina pectoris attack, transient myocardial ischemia, and some arrhythmia. The vagal cardiac function is commonly impaired in patients with coronary artery disease. Recently, an assessment of parasympathetic and sympathetic activities is now possible using neart rate spectral analysis. The spectral density of R-R interval variability contains two major components, high frequency (HF) power spectral density (<0.25Hz) and low frequency (LF) power spectral density (<0.15Hz), which have magnitudes that are quantitative markers of cardiac vagal activity and sympathetic activity with vagal modulation, respectively.

We analyzed the spectral components of R-R interval variability from 24 hour ambulatory holter monitoring in 20 controls and 20 patients with angina pectoris. The patients had no clinical evidence of hypertension, acute myocardial infarction, heart failure, arrhythmia or diabetes mellitus. Recording continued for 24 hours while the subject undertook his normal work and leisure activities. For power spectral analysis, 1024 hours beats was sampled at early morning, afternoon, evening and during sleeping.

The spectral component of R-R interval variability was unaffected by the time of day during the waking period, althought a significant decrease in LFCCV and HFCCV was observed during sleeping in controls(p<0.001). In comparison of two groups, patients with angina pectoris showed markedly diminished HFCCV values during waking period except during sleeping period. The R-R interval and LF/HFCCV and LF/HFCCV ratio at transient ischemic attack in patients with angina pectoris.

Autonomic cardiac control during the waking period shows little variation with the time of day in both groups. We observed that vagal cardiac function was reduced in patients with coronary artery disease by heart rate spectral analysis. It is suggested that ischemic changes in patients with coronary artery disease underlying reduced vagal cardiac function is associated with increased sympathetic activity.