Investigating Neurocardiac Autonomic Regulation and Cortical Excitability Measures in Patients with Major Depressive Disorder

Major depressive disorders (MDD) are among the most common psychiatric disorders affecting people worldwide. The steady increase in cases of depressive disorders has been mainly attributed to enhanced life stress. The association of this clinical condition with other systemic disorders, especially cardiac conditions, raises concerns about increased morbidity and mortality related to this disorder. Investigating neuro-cardiac regulation using heart rate variability (HRV) and cortical excitability using transcranial magnetic stimulation (TMS) in patients with depression can provide crucial insights to understand systemic involvement and possible therapeutic interventions. We recruited 60 patients suffering from moderate depression based on International Classification of Diseases ICD-10 criteria on treatment with Escitalopram for more than 2 months. The HRV measures and TMS techniques using cortical excitability measures with single and paired-pulse TMS measures were performed on all the patients and compared with age- and gender-matched healthy controls. Patients with depression showed significantly lesser standard deviation of normal-to-normal interval (SDNN), root mean square of successive differences (RMSSD), total power (TP), high frequency (HF) power, and increased low frequency (LF) power and LF/HF ratio which together indicate reduced HRV. Reduced short-interval intracortical inhibition (SICI), intracortical facilitation (ICF), and cortical silent period (CSP) (assessed by TMS) were also observed in patients with depression compared to healthy controls. Patients with depression showed decreased HRV, glutamatergic activity, gamma amino butyric acid-B (GABA-B) activity, and increased GABA-A activity. These findings suggest aberrant neuro-cardiac regulation and cortical excitability in this enigmatic disorder.