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.

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).

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.

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.

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.

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.