Abstracts

Closed-loop responsive electrical stimulation is an emerging therapy for the treatment of intractable epilepsy. This therapy is being evaluated in clinical trials of the Responsive Neurostimulator (RNSTM) system (NeuroPace, Inc.). During these trials, the RNS device was either 1) externalized and connected to cortical strip and depth electrodes used for pre-surgical monitoring, or 2) fully implanted and connected to permanent cortical strip and depth electrodes in ambulatory patients. Data from 35 epilepsy patients were evaluated. Electrocorticograms (ECoGs) containing stimulations delivered in response to detected events as well as non-treated detected events were stored by the RNS device and uploaded to a central database for subsequent analysis. Since there may be a correlation between acute electrographic responses to responsive stimulation and clinical effects, these electrographic responses were quantified and analyzed. Two event classes were identified for this analysis: 1) detection with stimulation ([quot][italic]stim[/italic][quot]), and 2) detections without stimulation ([quot][italic]non-stim[/italic][quot]). Electrographic activity was analyzed within 2-sec windows before and after each event, with an intervening 2-sec window ignored to avoid stimulation artifacts. Several features were quantified within these windows and the post-event vs. pre-event ratios and/or differences were calculated for each event (except those with stimulations occurring within either the pre-event or post-event window) and on each ECoG channel. The features analyzed include power spectral density (PSD), Line Length, and Area. Stimulated response ratios were compared between the [ldquo][italic]stim[/italic][rdquo] and [ldquo][italic]non-stim[/italic][rdquo] event classes. The PSD ratio responses, as well as the normalized PSD difference between pre- and post-event windows, averaged across all [quot][italic]stim[/italic][quot] events and across patients, showed a linear energy decrease, decreasing in magnitude with increasing frequency. In contrast, the [quot][italic]non-stim[/italic][quot] events showed a linear energy increase, increasing in magnitude with frequency, for frequencies above 20 Hz; and between 0.5 and 20 Hz they have a small energy decrease, increasing in magnitude with frequency. These observations suggest that closed-loop responsive electrical stimulation may acutely suppress epileptiform activity. The question of whether acute electrographic responses and suppression of epileptiform activity correlate with the clinical efficacy of responsive stimulation is currently under investigation. (Supported by NeuroPace, Inc.)