SUFU 2020: InterStim™ Micro System Performance Comparison in a Sheep Model

Scottsdale, Arizona ( This study aimed to demonstrate that a new rechargeable, current-controlled sacral neuromodulation (SNM) system (InterStim™ Micro) can activate sacral nerves at comparable stimulation amplitudes as the marketed, voltage-controlled InterStim™ II system. In addition, amplitudes required to evoke a muscle contraction were compared (motor threshold, MT) between the two systems.

The basic function of SNM systems is to modulate nerve activity by direct electrical stimulation which causes pelvic floor muscles to contract. Visual detection of external anal sphincter (EAS) contraction and/or toe flexion is used during lead placement, with responses evoked by low amplitude stimulation (less than 2V) suggesting close proximity to the nerve.

Using good laboratory practices, four female Polypay sheep were bilaterally implanted with one InterStim™ II SMN system (control group) and one InterStim™ Micro system (experimental group). The mechanisms by which muscles contract in response to nerve activation are conserved between sheep and humans. The body side and order of implants were randomized. After four weeks of recovery, MT was measured using four electrode configurations in each animal at four timepoints. Rate and pulse width were held constant. Electrode impedances were measured to convert current to voltage using Ohm’s law for direct comparison of stimulation amplitudes. Statistics were performed using Minitab (State College, PA) with p<0.05 significance.

The primary analysis compared MT amplitudes between the control and test systems using the electrode configuration which elicited the lowest MT at each time point. The mean lowest MT for the control and test systems were not different (Figure 1; Control: 0.8 ± 0.3 V, Test: 0.6 ± 0.2 V,n=16,p=0.105 paired t-test). Pooled data for all electrode configurations showed the mean MT for the control and test systems were also not different (Control:1.7 ± 1.0 V, Test:1.8 ± 1.6 V,n=64,p=0.489,paired t-test).

The authors concluded at the end that these results provide objective and quantified physiological evidence that when tested in a large animal model, the basic function of the new current-controlled InterStim™ Micro system is comparable to the voltage-controlled InterStim™ II system.

lowest motor threshold

Presented by: Katie C. Bittner1,2, Sarah J. Offutt1,2, Tina Billstrom3, Melissa A. Mattson3, Nathan Johnson4, Kellie Berg5, Lance Zirpel1,2

1Research and Core Technology, Restorative Therapies Group, Medtronic, Inc., Minneapolis, MN,Pelvic Health & Gastric Therapies, Restorative Therapies Group, Medtronic, Inc., Minneapolis, MN,Physiological Research Laboratories, Medtronic, Inc., Minneapolis, MN,Systems Engineering, Restorative Therapies Group, Medtronic, Inc., Minneapolis, MN,Clinical Research, Restorative Therapies Group, Medtronic, Inc., Minneapolis, MN

Written by: Bilal Farhan, MD, Assistant Professor, Division of Urology, University of Texas, Medical Branch, Texas; Twitter: @BilalfarhanMD, at the Society of Urodynamics, Female Pelvic Medicine & Urogenital Reconstruction Winter Meeting, SUFU 2020, February 25 - 29, 2020, Scottsdale, AZ