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Impedance Variances over Time for Depth and Strip Electrodes for Implanted Responsive Neurostimulation Devices

14th Annual Meeting of the North American Neuromodulation Society. Impedance Variances over Time for Depth and Strip Electrodes for Implanted Responsive Neurostimulation Devices. Chengyuan Wu, MD Ashwini Sharan, MD. Las Vegas, NV Friday, December 3, 2010. Disclosures.

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Impedance Variances over Time for Depth and Strip Electrodes for Implanted Responsive Neurostimulation Devices

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  1. 14th Annual Meeting of the North American Neuromodulation Society Impedance Variances over Time for Depth and Strip Electrodesfor Implanted Responsive Neurostimulation Devices Chengyuan Wu, MD Ashwini Sharan, MD Las Vegas, NV Friday, December 3, 2010

  2. Disclosures • Part of ongoing project conducted by Neuropace® to characterize long-term impedance changes across all subjects participating in the RNS studies

  3. Outline • Background • Methods • Results • Discussion • Conclusions http://www.neuropace.com/graphics/trials-fig1.gif

  4. Background • Responsive neurostimulation (Neuropace® - RNS®) is a potential treatment modality for intractable partial epilepsy • Detection and interruption of epileptiform activity prior to propagation • Intraparenchymal depth electrodes vs. Subdural strip electrodes • FDA-approved investigational device • Stimulation characteristics over time are important • Analysis of changes in electrode impedance http://www.neuropace.com/graphics/rns.jpg

  5. Methods • Single-center, retrospective review of impedance • October 2007 – September 2010 • 7 patients • 7 intraparenchymal depth electrodes • 7 subdural strip electrodes • Impedance of all 4 leads of each electrode measured in Ω and plotted over time

  6. Patient Data

  7. Patient Data

  8. Patient Data

  9. Patient Data

  10. Results

  11. Discussion • Subdural strip electrodes have higher mean impedance • Subdural strip electrodes have greater variability over time • Intraparenchymal depth electrodes have lower mean impedance and more stability • Net change in impedance values is not statistically significant for either type of electrode

  12. Conclusions • Stability of implanted device is of utmost importance • Changes in impedance alters stimulus delivered to brain • Contributing factors to changes in impedance: • Thickness/conductivity of encapsulation capsule • Surface contact area • Lead damage • Further analysis on greater number of patients required V = I × Ω

  13. Summary • Stability of implanted medical devices is of the utmost importance • Changes in impedance are not necessarily secondary to encapsulation by scar tissue • Depth electrodes demonstrate greater stability with less variability over time

  14. Thank You Questions?

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