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Non-linear cardiac dynamics and morning dip: an unsound circadian rhythm
1Department of Pediatrics, Hanyang University School of Medicine, Seoul, Korea.
Insights
Sudden cardiac death risk rises in the morning due to decreased heart rate complexity. This study reveals a daily pattern in cardiac dynamics, highlighting a vulnerable period in the early hours.
Area of Science:
- Cardiology
- Non-linear Dynamics
- Chronobiology
Background:
- Sudden cardiac death (SCD) incidence peaks in the morning.
- Reduced complexity in heart rate dynamics is linked to increased SCD risk.
- Understanding circadian variations in cardiac dynamics is crucial for SCD prediction and prevention.
Purpose of the Study:
- To investigate the circadian rhythm of cardiac dynamics complexity in healthy adults.
- To identify specific patterns of heart rate variability throughout a 24-hour period.
Main Methods:
- Collected 24-hour electrocardiographic (ECG) recordings from 30 healthy adults (aged 41-50).
- Analyzed RR interval data in 30-minute segments using non-linear dynamics algorithms (modified correlation dimension, Lyapunov exponent, approximate entropy, fractal dimension).
- Calculated normalized low-frequency (LF) and high-frequency (HF) components of heart rate variability.
Main Results:
- All four non-linear dynamics indexes exhibited a consistent circadian rhythm, peaking around midnight and dipping in the morning.
- A significant decline in cardiac dynamics complexity was observed during the late night and morning hours.
- In the morning, LF components increased while HF components decreased, indicating a shift in autonomic balance.
Conclusions:
- Cardiac dynamics complexity significantly decreases in the morning hours.
- This morning dip in complexity may contribute to the elevated risk of sudden cardiac death observed during this period.
- Findings suggest potential for chronobiological approaches in managing cardiovascular risk.
Abstract:
The frequency of sudden cardiac death increases in the morning. The relationship between decreased complexity of heart rate dynamics and sudden cardiac death has been documented. An understanding of circadian variation in the complexity of cardiac dynamics may be important to predict and prevent sudden cardiac death. Dynamic 24-h electrocardiographic recordings were obtained from 30 healthy ambulant subjects aged 41-50 years, and the digitized data were partitioned into sections of 30 min duration. For each section, four indexes obtained from separate algorithms of non-linear dynamics of the RR interval--modified correlation dimension, Lyapunov exponent, approximate entropy, and fractal dimension--were calculated. Normalized low-(0.04-0.15 hertz) and high-frequency (> 0.15 hertz) components were also calculated. All four indexes of non-linear dynamics showed a remarkably similar circadian rhythm: a prominent morning dip preceded by a steep decline during the late night, a recovery during the evening and a peak around midnight. In the morning, the low-frequency component rose rapidly with concomitant reduction in the high-frequency component. The complexity of cardiac dynamics decreases significantly in the morning, and this may contribute to the ominously increased rate of cardiac death in the morning hours.