Abstract
Studying heart rate dynamics would help understand the effects caused by a hyperkinetic heart in patients with hyperthyroidism. By using a multiscale entropy (MSE) analysis of heart rate dynamics derived from one-channel electrocardiogram recording, we aimed to compare the system complexity of heart rate dynamics between hyperthyroid patients and control subjects. A decreased MSE complexity index (CI) computed from MSE analysis reflects reduced system complexity. Compared with the control subjects (n = 37), the hyperthyroid patients (n = 37) revealed a significant decrease (p < 0.001) in MSE CI (hyperthyroid patients 10.21 ± 0.37 versus control subjects 14.08 ± 0.21), sample entropy for each scale factor (from 1 to 9), and high frequency power (HF) as well as a significant increase (p < 0.001) in low frequency power (LF) in normalized units (LF%) and ratio of LF to HF (LF/HF). In conclusion, besides cardiac autonomic dysfunction, the system complexity of heart rate dynamics is reduced in hyperthyroidism. This finding implies that the adaptability of the heart rate regulating system is impaired in hyperthyroid patients. Additionally, it might explain the exercise intolerance experienced by hyperthyroid patients. In addition, hyperthyroid patients and control subjects could be distinguished by the MSE CI computed from MSE analysis of heart rate dynamics.
Highlights
Hyperthyroidism is a clinical syndrome resulting from excessive thyroid hormones in the body
The hyperthyroid patients compared with the control subjects revealed a lower multiscale entropy (MSE) complexity index (CI)
Our results showed a decreased MSE CI in the hyperthyroid patients compared with the control subjects via MSE analysis of the heart rate dynamical system
Summary
Hyperthyroidism is a clinical syndrome resulting from excessive thyroid hormones in the body. Patients with hyperthyroidism present symptoms and signs induced by a hypermetabolic state due to the action of the excessive thyroid hormones. Palpitation and tachycardia are frequent cardiac manifestations in hyperthyroid patients. Studying heart rate dynamics would help understand the effects caused by a hyperkinetic heart in patients with hyperthyroidism. Previous studies mainly used linear analyses of heart rate variability (HRV) to investigate the heart rate dynamics in hyperthyroid patients [1,2,3]. Human physiological regulating systems consist of multiple mutually interacting controlling loops and operate under a nonlinear mechanism. Using linear HRV analysis alone might not fully elucidate the characteristics of the heart rate dynamical system in hyperthyroidism
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