NeuroPace | Resources | Publications

May 2003
Abstract presented at the Annual Meeting of the American Society for Stereotactic and Functional Neurosurgery

Michael Munz, MD; Robert D. Sweazey, PhD; Carla Barrett, MS; Audra Plenys Loftman, PhD; Harry Vinters, MD; Zaneta Popovska, BS; David A. Greene, BS

INTRODUCTION: An implantable Responsive NeuroStimulator System (RNSS) developed for intractable epilepsy will soon begin human trials. The RNSS is a system that is modifiable to the seizure dynamics of a specific patient and delivers therapy only in response to detected events. The RNSS consists of quadripolar depth and cortical strip leads, an advanced 8 contact Responsive NeuroStimulator (RNS), and programmer system (PS). The RNS includes the following capabilities: four-channel sensing, detection, stimulus delivery, stored ECOGís that can be downloaded into the PS, diagnostics and complex programmable therapies. The RNSS has been designed for use by clinicians. The objective of this study is to demonstrate the operational characteristics of the RNSS through chronic implantation and stimulation.

METHODS: Ten sheep were implanted with the lead system. Depth electrodes were placed stereotactically into the hippocampus and cortical strip electrodes were placed over the parietal and frontal lobes. Leads received 30 minutes of continuous stimulation per lead each week (50 Hz, 2.5 mA, 300 ms phase duration, biphasic) and weekly impedance measurements and signal recordings were performed. The animals were sacrificed at 4-9 months for histological analysis. Two additional animals were also implanted with RNS pulse generators, and a chronic replacement was demonstrated.

RESULTS: Stimulation of electrodes in the hippocampus produced afterdischarges suggesting that this model may be used for investigating kindling. The cortical electrodes showed slowing of activity after stimulation. Histopathological examination revealed no significant adverse tissue reaction to either implantation or stimulation.

CONCLUSIONS: The RNSS is a new approach for the treatment of epilepsy. Heretofore, stimulation therapy for epilepsy has used open- loop continuous or periodic stimulation paradigms. This study demonstrated the functionality of the RNSS in vivo and is an important part of the pre-clinical work required to begin the clinical trial of the system in patients.