Changes in Heart Rate Variability after Transcranial Direct Current Stimulation in Patients with Refractory Epilepsy

Abstract

Cathodal transcranial direct current stimulation (c-tDCS) is a non-invasive option for treatment of refractory epilepsy. However, it is still unknown whether this therapy has a positive stabilizing effect on the vegetative function of these patients. Heart Rate Variability (HRV) is considered an efficient tool to monitor the cardiac autonomic system, which has been correlated with the risk of Sudden Unexpected Death in Epilepsy (SUDEP). In this study, changes in HRV are investigated after c-tDCS of six patients ( $34.50 \pm 11.10$ years) with refractory epilepsy, which have been selected at the University Hospital, LMU Munich. Patients were categorized as responders ( $\mathrm{n}=2$ ), non-responders ( $\mathrm{n}=3$ ) and uncategorized ( $\mathrm{n}=1$ ). We analyzed 24 hours of electrophysiological data recorded before and after treatment, and computed HRV metrics (AVNN, SDNN, RMSD, pNN20, pNN50, LH/HF, 0V, IV, 2LV, 2UV, SD1 and SD2). All patients revealed a change in almost all HRV metrics post stimulation. Grouped all patients, there was a significant ( $\mathrm{p} ) change in RMSSD, pNN50, SD1 and LH/HF. For responders there was an increase in all time domain and non-linear metrics, which was not seen for non-responders. These results suggest that tDCS exerts significant changes in cardiovascular autonomic system in patients with refractory epilepsy. HRV metrics may also serve as biomarkers of the response to tDCS stimulation. A larger dataset is being gathered for further analysis.