Soterix Medical introduced the High Definition-transcranial Electrical Stimulation (HD-tES) approach in 2008 as the first transcranial system capable of delivering optimized neuromodulation. The High Definition (HD) approach uses smaller-size electrodes that enable positioning them in arrays, thereby controlling targeting of brain regions (focal or widespread) in an application-specific manner. Conventional Electroconvulsive Therapy (ECT) is delivered via two large scalp electrodes that limit electrode placement options. While historically it was considered that a generalized seizure was needed for efficacy, approaches that result in a more restricted current flow such as right unilateral (RUL) electrode placement, focal electrically administered seizure therapy (FEAST), and magnetic seizure therapy (MST) have shown less cognitive risk with comparable efficacy. Since the cognitive side effects are thought to be related to stimulation of “non-target” regions (or brain structures not implicated in Depression), continuing to develop optimized targeting approaches presents an opportunity to further optimize risk/benefit profile, and thereby potentially lifting the stigma, long associated with ECT practice. Extending the HD approach to ECT or HD-ECT is therefore intended to spur a new wave of clinical research and eventually enable safer and more efficacious ECT treatment procedures.
The 4X1 High Definition–Electroconvulsive Therapy (HD-ECT) Interface is an accessory to a single channel Electroconvulsive Therapy (ECT) stimulator and does not function as a stand-alone electrical stimulator or generator. The 4X1 HD-ECT device is designed to be used as an interface device between the ECT device and 5 stimulation leads; where 4 leads are connected to one lead of the ECT stimulator while the remaining 5th lead is connected to the second lead of the ECT stimulator. The 4X1 HD-ECT passively splits current from 2 leads to 5 leads. It also has an optional ATTENUATION feature which lets the operator deliver reduced current to the subject starting at 200 mA.
The device operates in two modes: SCAN and PASS mode. The SCAN MODE is used to determine lead quality values prior to switching to the PASS MODE. In PASS MODE, the 4X1 HD-ECT acts as a passive current divider. The PASS MODE also provides the option for attenuating ECT device output. The attenuation desired can be set by entering the output current value on the device. The PASS MODE does not modulate the waveform of the ECT device as long as the attenuation feature is disabled.
These are small specialized donut-shaped electrodes that are held in HD Electrode Holders.
This gel serves as the conductive medium between the HD-Electrode and the subject’s scalp.
HD-Electrodes are held in these holders. The holder is filled with HD-GEL. A cap locks the electrode and gel combination in place.
The cap follows the EEG 10-10 convention and includes slits that allow holding the HD Electrode holder at desired locations. The electrode locations are printed on cap preventing use error. Remaining locations may be used for conventional EEG as desired.
The HD approach has been validated for low intensity (~2 mA) application such as transcranial direct current stimulation (tDCS / tES) in scores of publications - ranging from neurophysiological (Kuo 2013), behavioral (Naka 2018; Donaldson 2019; Sasia 2021), and therapeutic application (Castillo-Saavedra 2016; Jacquemin 2018; Jog 2021). In contrast to tDCS, which produces no evoked response, the passage of short (50 μs) high-voltage pulses (max: 1kV / 1.5A) through scalp electrodes (Transcranial Electrical Stimulation: TES) activates the motor cortex and triggers MEPs. This can be used as a clear marker of current intensity and location in the brain. In collaboration with Burke Rehabilitation Institute, “4X1 HD-TES” was shown to not only trigger MEPs but provide comparable focalization at 6 cm diameter resolution (Edwards 2013). The study demonstrated that in spite of the tight placement of scalp stimulation electrodes (4X1 array), current delivery was focal and did not spread outside the array. This study serves as early validation that HD-Electrodes (electrodes) can deliver high current needed for ECT in a safe fashion.