First Demonstration Recording Evoked Biosignals from Concordant Stimulating Electrodes Using Cylindrical Leads near Peripheral Nerves

Introduction: While PNS can provide excellent chronic pain relief in many patients, areas that need improvement. Biosignals such as an evoked compound action potential (ECAP) or compound muscle action potential (CMAP) have been shown to optimize stimulation dosing in SCS (1,2) and potentially assist in lead placement, long-term outcomes, and programming (3). However, recording of ECAPs is significantly more challenging in PNS than in SCS due to varied lead placement relative to the target tissue and excitable tissue volume. We investigated whether recording relevant biosignals while performing PNS of peripheral nerve(s) using commercial cylindrical leads is feasible.

Methods: Porcine animals (n=3) were utilized for experiments and approved by a local IACUC. Animals were anaesthetized with isoflurane, and cylindrical leads (diameter 1.5 mm, 7 mm center-to-center spacing) were first placed percutaneously in proximity of the sciatic nerve before the tibial/peroneal branch with ultrasound imaging guidance or an open surgical approach. A proprietary combination of artifact cancellation techniques was developed to minimize the artifact due to stimulation. Signals were recorded simultaneously from the pair of electrodes delivering stimulation and from a non-stimulated pair. Recordings were analyzed for the presence of ECAPs as well as CMAP responses.

Results: For the first time ever, we successfully demonstrated the ability to record ECAP on the same electrode pair used for stimulation (Figure 1a). ECAPs recorded off the stimulation pair exhibited a clear threshold and rapid growth and were earlier and larger than ECAPs recorded off the adjacent pair. In addition, we could detect CMAP signals off the percutaneous lead (Figure 1b). CMAP thresholds closely matched the ECAP thresholds, suggesting that a CMAP signal may be a proxy for the ECAP signal in situations where the ECAP signal is unavailable while encoding different information.

Conclusion: This study marks the first-ever demonstration of in vivo recording of ECAPs on the same electrode pair as the stimulation electrodes. Results from these experiments demonstrate the feasibility of recording robust evoked potentials from peripheral nerves with lead constructs typically utilized in commercial chronic pain applications. Given the varied nature of placement of PNS leads, this new technique may be an enabler of closed-loop PNS stimulation. In addition, we demonstrate that the CMAPs can be a proxy for ECAP stimulation and may be an alternative to detecting an ECAP when PNS is applied to a mixed nerve.