Circadian patterns of heart rate variability in normals, chronic stable angina and diabetes mellitus

The purpose of our investigation was to compare circadian patterns of heart rate variability as assessed by 24-h ambulatory electrocardiographic (ECG) recordings in normal subjects, chronic stable angina, and Type 1 diabetes mellitus. The study population consisted of three groups: 12 normal subjects, 23 chronic angina patients, and 23 Type 1 diabetics. For purposes of analyzing circadian variation, the ECG recordings were divided into daytime (08:00–00.00 h) and night-time (00:00–08:00 h) periods. Analysis was performed for all time and frequency domain measures of heart rate variability, attempting to identify differences in day-to-night variability among these three groups. All time domain parameters except standard deviation of all 5-min mean RR intervals, and all frequency domain indices maintain significant circadian variations (P<0.0001), with the greatest day to night variation seen in normals, the least in diabetics, and intermediate values in chronic angina. These changes in heart rate variability circadian rhythms reflect significant reductions in cardiac parasympathetic activity with the most marked reduction in nocturnal vagal activity. Given the circadian pattern of myocardial ischemia and infarction, these data suggest that quantification of the magnitude of circadian variation in heart rate variability may have the potential to further risk stratify chronic angina and diabetes for future cardiac events.