Abnormal circadian rhythm of heart rate variability and their association with symptoms in patients with major depressive disorder

Heart rate variability (HRV) is often reduced in patients with major depressive disorder (MDD) and is linked to symptoms. However, prior studies have mainly focused on short-term HRV, with limited exploration of the 24-h HRV circadian rhythm, despite its ability to comprehensively capture overall HRV distribution and dynamic fluctuations. In this study, we investigated the circadian rhythms of 24-h HRV indices in patients with MDD and their associations with symptom severity. We recorded 24-h electrocardiograms in 73 patients with MDD (53 in major depressive episode and 20 in remission period) and 31 healthy controls. An extended cosine model was used to model the circadian rhythm of six HRV indices by five parameters: the mesor, amplitude, duty cycle, curve smoothness, and acrophase. Symptom severity was evaluated using the Hamilton Depression Scale and Hamilton Anxiety Scale. Compared with the control group, patients with MDD had a significantly smaller SampEn mesor, higher HF duty cycle, and lower heart rate (HR) duty cycle. They also had a significantly higher curve smoothness for HR, RMSSD, and HF. The mesor for SampEn, along with the curve smoothness for HR and ln RMSSD, were associated with certain symptoms in patients with MDD. Limitations. The cross-sectional design and psychiatric treatment of most patients with MDD limited our findings. Patients with MDD exhibit abnormal HRV circadian rhythms that are associated with symptoms. Moreover, 24-h ECG monitoring may potentially serve as an adjunct value to objectively evaluate clinical symptoms in these patients.