Presented at the 2012 AAPM Annual Meeting « Back

RestoreSensor Study Results: SCS Therapy Impedance Does Not Vary Significantly with Changes in Body Position

David M. Schultz, MD, dschultz@painphysicians.com¹, Lynn R. Webster, MD², Ye Tan, MS³, Dennis Skelton, BS³, Mark Sun, PhD³, Eric Panken, MS³, (1) MAPS Applied Research Center, Edina, Minnesota, (2) Lifetree Clinical Research, Salt Lake City, Utah, (3) Medtronic, Inc., Minneapolis, Minnesota

Introduction: Studies have reported spinal cord stimulation therapy impedance changes occur within several weeks after implant and impedance does not correlate with body position. We report on impedance variations during a 16-week study. Materials and Methods: Patients in a prospective, multicenter, randomized crossover, IRB-approved study of position-adaptive stimulation were implanted with a RestoreSensor™ neurostimulator (Medtronic, Inc., Minneapolis, MN). Impedance was recorded in supine and upright positions at 1, 4, 10, and 16 weeks post-implant. Group impedances by visit and position from all active programs were averaged for each patient. Variation in impedance with position over time and relative percent difference between upright and supine positions were analyzed. Results: In 76 implanted patients (mean age 52.8 years, 59% female) median impedance was 346 Ohms (upright) and 347 Ohms (supine) at 1 week post-implant , and increased to 441 Ohms (upright) and 444 Ohms (supine) at 16 weeks post-implant (Figure 1). The median impedances were nearly the same between the upright and supine positions at each follow-up visit. The effect of position was not statistically significant (p = 0.610). The average relative percent difference in impedance between upright and supine positions was 3% (SD 8.6%). Conclusions: Differences in impedance between the upright and supine positions were insignificant. Impedance for both positions increased initially and stabilized over time. Impedance does not vary with body position although impedance increases during the healing period when electrode encapsulation occurs.

Funding: The RestoreSensor study was funded by Medtronic, Inc.

Figure 1. Median group impedance by visit and position