Abstracts

Eight adults with intractable partial seizures have received a cranially implanted responsive cortical neurostimulator (NeuroPace RNS[trade]) at the Medical College of Georgia (MCG) as part of an FDA approved trial to evaluate safety and to assess effects on seizures. Electrical stimulation configurations are broadly divided into mono-polar and bipolar paradigms. Debate exists regarding whether the most effective stimulation paradigm includes monopolar or bipolar configurations, since several variables such as etiology, location of seizure focus or foci, size of epileptogenic zone, and rate and pathway of spread of electrical activity may impact therapeutic response. We analyzed the various electrical stimulation paradigms according to the effect on seizure frequency in six patients participating in an open-label period of the trial. All electrode configurations implemented in the six open label patients at MCG and their respective seizure outcomes were reviewed. Etiology, seizure focus or foci, relative size of epileptogenic zone, and rate and pathway of spread of epileptic activity were noted in all patients. The mean time since device implantation was 8 months (range 6-10). Three patients had multiple seizure foci (involving both hemispheres). All patients underwent lead implantation into one (5/6; 4 left, 1 right) or both (1/6) temporal regions. Only one patient (with bilateral hippocampal sclerosis) received one lead. Cathodal monopolar stimulation was used in 5 of 6 patients and bipolar stimulation was used in 3 of 6 patients; 2/3 with depth electrodes only and 1/3 with two 4-contact subdural strips. Five of six patients have experienced a reduction in seizure frequency of 45% or greater since device implantation (four patients have experienced a reduction in seizure frequency of 75% or greater); one patient is seizure-free. Seizures have increased in one patient with multiple seizure foci. Seizure frequency was reduced in a small number of adults with medically intractable partial seizures using either cathodal monopolar or bipolar stimulation paradigms. Though bipolar stimulation was used more exclusively in patients with depth electrodes, bipolar (intra-lead) stimulation appeared to have a favorable effect in patients with small seizure foci (e.g. hippocampal sclerosis), whereas cathodal monopolar stimulation may be effective in patients with larger epileptogenic zones or multiple epileptic foci. (Supported by NeuroPace, Inc.)