Electric field strength induced by electroconvulsive therapy is associated with clinical outcome

Egill Axfjord Fridgeirsson,Zhi-De Deng,Damiaan Denys,Jeroen A Van Waarde,Guido A Van Wingen

doi:10.1016/j.nicl.2021.102581

Abstract

The clinical effect of electroconvulsive therapy (ECT) is mediated by eliciting a generalized seizure, which is achieved by applying electrical current to the head via scalp electrodes. The anatomy of the head influences the distribution of current flow in each brain region. Here, we investigated whether individual differences in simulated local electrical field strength are associated with ECT efficacy. We modeled the electric field of 67 depressed patients receiving ECT. Patient’s T1 magnetic resonance images were segmented, conductivities were assigned to each tissue and the finite element method was used to solve for the electric field induced by the electrodes. We investigated the correlation between modelled electric field and ECT outcome using voxel-wise general linear models. The difference between bilateral (BL) and right unilateral (RUL) electrode placement was striking. Even within electrode configuration, there was substantial variability between patients. For the modeled BL placement, stronger electric field strengths appeared in the left hemisphere and part of the right temporal lobe. Importantly, a stronger electric field in the temporal lobes was associated with less optimal ECT response in patients treated with BL-ECT. No significant differences in electric field distributions were found between responders and non-responders to RUL-ECT. These results suggest that overstimulation of the temporal lobes during BL stimulation has negative consequences on treatment outcome. If replicated, individualized pre-ECT computer-modelled electric field distributions may inform the development of patient-specific ECT protocols.

Highlights

Electroconvulsive therapy (ECT), a form of transcranial electrical stimulation (TES), is a highly effective treatment, especially in patients suffering major depressive episodes (MDE)
67 patients were included of which 25 were treated only with right unilateral (RUL) electrode placement, 16 with only BL placement and 26 pa tients switched from RUL to BL placement
Using a computer model derived from individual magnetic resonance image (MRI) data, electric field distributions in brains of electroconvulsive therapy (ECT)-patients showed significant vari ability between patients, especially comparing RUL and BL electrode placement

Summary

Introduction

Electroconvulsive therapy (ECT), a form of transcranial electrical stimulation (TES), is a highly effective treatment, especially in patients suffering major depressive episodes (MDE). All treatment modalities with TES (e.g., ECT, transcranial direct current stimulation [tDCS] and transcranial alternate current stimula tion [tACS] (Saturnino et al, 2019) induce electric fields in the human brain, but in ECT much higher electrical currents are used - reaching larger brain areas - compared to tDCS and tACS. Modern-day ECT uses constant current (0.8 or 0.9 Ampere) administered in brief pulses (typically with a pulse width of 0.25–1.5 ms) in varying frequencies and stimulus train dura tions (typically up to 8 s) (Peterchev et al, 2010). Several positions are in use, such as the right unilateral (RUL), bifrontal, and bilateral (BL) electrode placements, delivering the therapeutic electrical charge differently to the patients’ brain

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