NeuroPace | Resources | Publications

November 2003
Abstract Presented at the Annual Meeting of the Society for Neuroscience

M. Munz, MD ^1,2; R. Sweazey, PhD ^2,3; C. Barrett, MS ³; A. Plenys Loftman, PhD ⁴; D. Potts, BS ⁴; D. Greene, BS ⁴

¹ Anat. & Cell Biol., Fort Wayne Neurological Ctr., Ft. Wayne, IN, USA; ² Biol., Indiana Univ. Sch. Med., Ft. Wayne, IN, USA; ³ IPFW, Ft. Wayne, IN, USA; ⁴ NeuroPace, Inc, Mountain View, CA, USA

No device is available that can detect epileptiform activity and deliver therapeutic electrical stimulation. Our study examined the cranial implantation, chronic replacement and essential operating characteristics of the Responsive NeuroStimulator (RNS™) system developed for the treatment of medically refractory epilepsy in humans. The RNS system consists of a curved shape pulse generator, cortical strip lead, depth lead (3.5 or 10 mm spacing), implantable ferrule for cranial stabilization and to facilitate replacement, and an advanced programming system. Twelve-month old Suffolk sheep were implanted as follows: bilateral quadripolar hippocampal depth leads were placed stereotactically. A cranial defect shaped like the RNS ferrule was created using neurosurgical tools; the inner table of the cranium was left intact. The ferrule was then fixated to the cranium using titanium screws. The RNS system was then attached to the ferrule and leads, and the wounds closed. Three months after implant, the devices were exposed and the pulse generators were replaced to demonstrate the replacement procedure. Device strain relief mechanisms allowed easy exposure and removal of leads from the first RNS devices and placement of the replacement RNS devices. The ferrules were encapsulated in vascularized fibrous sheaths that were separate and distinct from sheaths encapsulating the devices. Replacement time was less than one hour. Subsequent operation of the RNS systems in vivo showed nominal operation. EEG samples were stored in the RNS device, downloaded with transcutaneous telemetry and examined offline. EEG samples from similarly implanted leads were stored before and after 30 min continuous 50 Hz hippocampal stimulation as part of lead neural tissue response safety testing.