Final 24-Month Outcomes with a Flexible Closed Loop Spinal Cord Stimulation System

Introduction: Closed loop (CL) spinal cord stimulation (SCS) systems automatically adjust stimulation output with the goal of minimizing therapy dose fluctuations and preventing overstimulation and understimulation. The evoked compound action potential (ECAP) amplitude, a measure of the dose reaching the spinal cord, was sensed and used to determine the need to adjust and titrate the amplitude on a pulse-by-pulse basis.[1] This closed-loop system is flexible in that it can be programmed with low- or high-frequency stimulation paradigms at amplitudes set above or below perception threshold. Here we report subject experience, low back pain outcomes, and composite outcomes[2] at the 24-month follow-up.

Methods: This prospective, multicenter, single-arm study evaluated the long-term patient experience with a flexible CL-SCS system (NCT05177354). The study is ongoing and has finished the last follow-up visit as of July 28, 2025. The primary goal was to demonstrate reduction in overstimulation with CL versus open-loop SCS at 1-month during in-clinic testing.[2] This in-clinic testing was repeated at the 3- and 12-month visits. An additional post-hoc analysis will be conducted, characterizing a composite outcome3 that includes pain intensity, sleep, health-related quality of life, disability, and mood at 24-month follow-up.

Results: Ninety-four subjects were enrolled, 75 trialed and 60 were implanted with the study device, and 42 completed the 24-month visit. Eighteen subjects exited between implant and the 24-month visit due to lead revision (n=1), non-compliance with study (n=4), lost to follow-up (n=3), confounding or new pain condition (n=7), IPG pocket dehiscence and infection secondary to shingles (n=1), anxiety (n=1), and underwent spine surgery (n=1). Demographics of subjects in the 24-month completers analysis are shown in Table 1. Of the 42 subjects who completed the 24-month visit, 35 reported baseline back pain ≥ 60 mm. At 24-months, 80.0% of subjects (28/35) were considered low-back pain responders. The paired mean (± SD) back pain VAS scores at baseline and 24-month follow-up were 78.2mm (± 9.53) and 22.7mm (± 22.78), respectively corresponding to a mean change from baseline of -55.4mm (± 24.57) or a -70.55% reduction (Figure 1). In all subjects who completed the 24-month visit, 85.7% (36/42) of subjects were responders in ≥ 3 domains of the composite outcome (Table 2). In all subjects at 24-months, 97.6% (41/42) were very/somewhat satisfied with therapy, and 100% (42/42) would definitely/probably recommend the therapy to others.

Conclusion: These findings highlight the benefits of a flexible, ECAP-based CL-SCS system. Subjects experienced sustained pain relief through 24-months as well as significant improvements in other quality-of-life domains. Offering a preferred and more consistent therapy experience to patients may lead to increased therapy utilization, reliable long-term therapy outcomes, and thereby reduce explants for lack of efficacy.

Keyword 1: Spinal Cord Stimulation

Keyword 2: Chronic Pain

Keyword 3: Closed-Loop

Keyword 4: Evoked Compound Action Potential

Keyword 5: Low Back Pain

References : 1. Vallejo R, Chakravarthy K, Will A, Trutnau K, Dinsmoor D. A New Direction for Closed-Loop Spinal Cord Stimulation: Combining Contemporary Therapy Paradigms with Evoked Compound Action Potential Sensing. J Pain Res. 2021;14:3909-3918. Published 2021 Dec 29.
2. Mohabbati V, Sullivan R, Yu J, et al. Early Outcomes with a Flexible ECAP Based Closed Loop Using Multiplexed Spinal Cord Stimulation Waveforms-Single-arm Study with In-clinic Randomized Crossover Testing. Pain Med. Published online May 16, 2025.
3. Levy RM, Mekhail N, Abd-Elsayed A, et al. Holistic Treatment Response: An International Expert Panel Definition and Criteria for a New Paradigm in the Assessment of Clinical Outcomes of Spinal Cord Stimulation. Neuromodulation. 2023;26(5):1015-1022.

Funding: This study was funded by Medtronic