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Heart. 1998 May; 79(5): 493–496.
PMCID: PMC1728677
Copyright notice
Circadian rhythm of the signal averaged electrocardiogram and its relation to heart rate variability in healthy subjects
M Nakagawa, T Iwao, S Ishida, H Yonemochi, T Fujino, T Saikawa, and M Ito
Department of Laboratory Medicine, Oita Medical University, Japan.
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Abstract
Objective—To examine the circadian variation in the signal averaged electrocardiogram (saECG) and heart rate variability and investigate their relations in healthy subjects.
Methods—24 hour ECGs were obtained with a three channel recorder using bipolar X, Y, and Z leads in 20 healthy subjects. The following variables were determined hourly: heart rate, filtered QRS (f-QRS) duration, low and high frequency components of heart rate variability (LF and HF), and the LF/HF ratio.
Results—Heart rate, f-QRS duration, HF, and the LF/HF ratio showed significant circadian rhythms, as determined by the single cosinor method. Heart rate and the LF/HF ratio increased during daytime, and f-QRS duration and HF increased at night. f-QRS duration was negatively correlated with heart rate (r = 0.95, p < 0.001) and the LF/HF ratio (r = 0.94, p < 0.001) and positively with HF (r = 0.93, p < 0.001).
Conclusions—f-QRS duration has a significant circadian rhythm in healthy subjects and is closely related to the circadian rhythm of autonomic tone.

Keywords: signal averaged ECG;  f-QRS duration;  circadian rhythm;  heart rate variability
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Figure 1
Figure 1  
Circadian rhythm of the hourly means of heart rate (A), f-QRS duration (B), ln HF (C), and ln LF/HF (D) in 20 subjects. Solid lines represent curves fitted to the data by the single cosinor method. LF and HF, low and high frequency components, (more ...)
Figure 2
Figure 2  
Signal averaged electrocardiogram recordings from a healthy 24 year old woman at 05:00 (A) and at 11:00 (B). Note that the increase of the heart rate from 63 (A) to 76 beats/min (B) was associated with an increase in ln LF/HF (more ...)
Figure 3
Figure 3  
Correlations between the hourly means of the f-QRS duration and heart rate (A), ln HF (B), and ln LF/HF (C) in 20 subjects. LF and HF, low and high frequency components, respectively, of heart rate variability; LF/HF, LF to HF ratio.
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