Circadian rhythm of the signal averaged electrocardiogram and its relation to heart rate variability in healthy subjects

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. (Heart 1998;79:493-496) Keywords: signal averaged ECG; f-QRS duration; circadian rhythm; heart rate variability Signal averaged electrocardiography (saECG) is a non-invasive method of detecting the substrate for malignant ventricular arrhythmias and is widely used to identify individuals at high risk for such arrhythmias and for sudden cardiac death. [1][2][3][4][5] Although the saECG has been assumed to measure fixed parameters, several studies have shown that these are altered by changes in factors such as heart rate and autonomic tone.6-8 Analysis of heart rate variability has been used to evaluate cardiac autonomic tone. 9-11Heart rate, heart rate variability, cardiac autonomic tone, and ventricular arrhythmias are known to have a circadian rhythm, [12][13][14][15][16] but information on the possibility of a circadian rhythm of the saECG and on the contribution of circadian fluctuations in autonomic function to the saECG is limited. We investigated whether the saECG has a circadian rhythm in healthy subjects and examined the relation between circadian fluctuations of the saECG and heart rate variability. Methods STUDY POPULATIONWe analysed 24 hour ECG recordings obtained in 44 healthy volunteers (28 men and 16 women, mean age (SD): 28.2 (3.3) years) in whom no abnormalities were detected by the medical history, physical examination, biochemical profile, 12 lead ECG, echocardiogram, or chest x ray. No subjects were on drug treatment. ANALYSIS OF 24 HOUR ECG RECORDINGSThe 24 hour ECG recordings were made with a three channel recorder (model 459, Del Mar Avionics, Irvine, California, USA) using bipolar leads X, Y, and Z. saECG analysisSignal averaging was performed on the data obtained from the first 500 seconds of every hour over the 24 hour period and filtered with a bidirectional filter at 40 to 250 Hz. The filtered leads were combined to form a vector as: √X 2 +Y 2 +Z 2 . The QRS onset and oVset were determined by a computer algorithm. The computer determined QRS oVset point w...

Modeling autonomic regulation of cardiac function and heart rate variability in human endotoxemia

“…This is because, in the model, T par is predicted to pass relatively close to zero in its diurnal cycle, so in endotoxemia, there is not much further for it to fall. While this result may seem unintuitive, it matches with experimental results showing that the drop from maximum to minimum values during circadian rhythms in HF and LF (33,43,53), and the depression in HF and LF due to endotoxemia (28,35,36) can both be anywhere from 50 to 90%, depending on experimental protocol. However, by looking at Poincaré maps (compare Figs.…”

“…1c) and Tpar (Eq. 1d), which are ultimately linked to circadian rhythms in HR that match well with experimental data showing that HR peaks during the day and is lower at night (53).…”

“…HF and LF power have been observed to exhibit circadian rhythms under normal conditions (33,43,53). In human endotoxemia, HF and LF power both decrease acutely before recovering (28,35,36).…”

“…Sympathetic activity increases HR, while parasympathetic activity decreases HR; therefore, combining models that represent autonomic activity in inflammation (23) and circadian rhythms in inflammation (70) generates variables reflecting circadian rhythms in sympathetic and parasympathetic activity at the SA node. These circadian autonomic activities lead to diurnal patterns in both HR and HRV (33,43,53). Circadian rhythms are hypothesized to express sympathetic activity as proportional to autonomic modulation and parasympathetic activity as inversely proportional.…”

“…Then, the peaks in the power spectrum fall directly within the HF and LF bands, facilitating the use of standard methods of calculating HF and LF power to study model output. The amplitudes of the HF and LF sinusoids depend on T par, which produces homeostatic circadian rhythms in HRV (33,43,53) as well as acute suppression of HRV in endotoxemia (28,35,36).…”