Stimulation output and tissue impedance over 6-months of sacral neuromodulation therapy with a constant current system

de Wachter S1, McCrery R2, Lane F3, Benson K4, Taylor C5, Padron O6, Blok B7, Pezzella A8, Gruenenfelder J9, Pakzad M10, Perrouin-Verbe M11, Van Kerrebroeck P12, Mangel J13, Peters K14, Kennelly M15, Shapiro A16, Lee U17, Comiter C18, Mueller M19, Goldman H20

Research Type

Clinical

Abstract Category

Overactive Bladder

Abstract 47
OAB: Neuromodulation and Unusual Associations
Scientific Podium Short Oral Session 5
Friday 20th November 2020
11:07 - 11:15
Pavilion 9
Urgency Urinary Incontinence Detrusor Overactivity Neuromodulation Overactive Bladder
1. Department of Urology, University Hospital Antwerpen, Edegem, Belgium, 2. Adult & Pediatric Urology & Urogynecology, Omaha, Nebraska, 3. University of California, Irvine, California, 4. Sanford Hospital, Sioux Falls, South Dakota, 5. Taylor Surgical Arts, Harrison, Arkansas, 6. Florida Urology Partners, Tampa, Florida, 7. Department of Urology, Erasmus MC, Rotterdam, The Netherlands, 8. Southern Urogynecology, West Columbia, South Carolina, 9. Orange County Urology Associates, Laguna Hills, California, 10. University College London Hospital, Marylebone, London, 11. CHU de Nantes Hotel Dieu, Nantes, France, 12. Maastricht University Medical Centre, Maastricht, The Netherlands, 13. MetroHealth, Cleveland, Ohio, 14. Beaumont Health, Royal Oak, Michigan, 15. Carolinas Healthcare System Charlotte, North Carolina, 16. Chesapeake Urology Research Associates, Owings Mills, Maryland, 17. Virginia Mason, Seattle, Washington, 18. Stanford University, Palo Alto, California, 19. Northwestern University, Chicago, Illinois, 20. Cleveland Clinic, Cleveland, Ohio
Presenter
S

Stefan de Wachter

Links

Abstract

Hypothesis / aims of study
Neuromodulation systems can deliver electrical stimulation either as constant voltage (CV) or constant current (CC). CC systems adjust their output to deliver consistent stimulation current to the body when tissue impedance changes, while a CV system allows the current output to vary with impedance, which may impact stimulation efficacy. Sacral neuromodulation (SNM) is a guideline-recommended neuromodulation treatment for urinary dysfunctions and fecal incontinence [1]. The ARTISAN-SNM study was designed to evaluate the safety and effectiveness of the Axonics System, a constant current SNM system, for the treatment of urinary urgency incontinence (UUI). This abstract provides a summary of the stimulation output and impedance over the first 6 months of therapy.
Study design, materials and methods
129 participants with UUI across 19 centers were treated with the Axonics System. Participants were implanted with a tined lead and neurostimulator in a non-staged procedure and programmed post-operatively or within 2 weeks of implant. At 6-months, 125 participants are included in this analysis, which utilizes their stimulation parameter and impedance data recorded at their study visits. Impedance values reported here is the impedance at the active stimulation electrodes, and voltage was calculated using Ohm’s law (Voltage =Impedance * Current).
Results
Across the 125 participants, active electrode impedance increased from 1,004 Ω (±310) at activation to 1,460 Ω (±355) at 6 months, an average increase of 42%. Stimulation current increased from 1.1 mA (±0.5) at activation to 1.6 (±0.8) at 6 months, and the stimulation output voltage increased from 1.1 V (±0.8) to 2.3 V (±1.2). Stimulation output voltage increased by 109%, while stimulation current increased by 45%. 

Sub-analysis was conducted in 78 participants that remained on the same active electrode configuration from 1 month to 6 months (Figure 1). The average stimulation amplitude across the 78 participants increased from 1.41 mA to 1.55 mA, an increase of 10%. During this period, the voltage output increased from 1.48 V to 2.26 V, an increase of 53%. Across these participants, 68% of the participants experienced a <25% increase in current output at 6 months, including 35% experiencing a <5% increase. In contrast, 75% of participants experienced a >50% increase in output voltage, including 24% experiencing a >75% increase compared to activation.
Interpretation of results
Electrode impedance increases significantly in the first 6 months of SNM therapy. Stimulation with a constant current SNM system results in a modest increase in stimulation current while stimulation output voltage increases by a significantly greater degree.
Concluding message
Constant current SNM systems may reduce patient or clinician adjustment of therapy by providing consistent stimulation current to the sacral nerve despite changing tissue impedance at the stimulating electrodes.
Figure 1 Figure 1. Left: Change in impedance of the active electrode configuration from 0 to 6 months post-implant. Right: Current and voltage output from 1 month to 6 months post-activation.
References
  1. Gormley EA, Lightner DJ, Faraday M, Vasavada SP. Diagnosis and treatment of overactive bladder (non-neurogenic) in adults: AUA/SUFU guideline amendment. J Urol. 2015 May;193(5):1572-80.
Disclosures
Funding Axonics Modulation Technologies, Inc. Clinical Trial Yes Registration Number NCT03327948 RCT No Subjects Human Ethics Committee IRB Helsinki Yes Informed Consent Yes