Characterization and applications of evoked responses during epidural electrical stimulation

Abstract

Background Epidural electrical stimulation (EES) of the spinal cord has been FDA approved and used therapeutically for decades. However, there is still not a clear understanding of the local neural substrates and consequently the mechanism of action responsible for the therapeutic effects. Method Epidural spinal recordings (ESR) are collected from the electrodes placed in the epidural space. ESR contains multi-modality signal components such as the evoked neural response (due to tonic or BurstDR™ waveforms), evoked muscle response, stimulation artifact, and cardiac response. The tonic stimulation evoked compound action potential (ECAP) is one of the components in ESR and has been proposed recently to measure the accumulative local potentials from large populations of neuronal fibers during EES. Result Here, we first review and investigate the referencing strategies, as they apply to ECAP component in ESR in the domestic swine animal model. We then examine how ECAP component can be used to sense lead migration, an adverse outcome following lead placement that can reduce therapeutic efficacy. Lastly, we show and isolate concurrent activation of local back and leg muscles during EES, demonstrating that the ESR obtained from the recording contacts contain both ECAP and EMG components. Conclusion These findings may further guide the implementation of recording and reference contacts in an implantable EES system and provide preliminary evidence for the utility of ECAP component in ESR to detect lead migration. We expect these results to facilitate future development of EES methodology and implementation of use of different components in ESR to improve EES therapy.

The role of spinal cord neuroanatomy in the variances of epidural spinal recordings

“…Observing the evoked responses, such as evoked compound action potentials (ECAPs) and later responses, in epidural spinal recordings (ESRs) following SCS offers insight into the synchronous firing of nerve fibers in the spinal dorsal columns as well as SCS-induced muscle contractions near the stimulation site (Parker et al 2012 ; Parker et al 2013 ; Parker et al 2020 ; Verma et al 2023 ; Falowski, et al 2022 ). Activation of the dorsal spinal columns has previously been linked to the orientation of electrical fields along the target fibers (Struijk et al 1993 ; Rattay 1999 ; Rattay et al 2000 ).…”

Epidural Spinal Cord Recordings (ESRs): Sources of Artifact in Stimulation Evoked Compound Action Potentials

“…Therefore, leads may not be in a location that is directly comparable to an animal model. A reference was placed in adipose tissue near the spinal cord to avoid differential subtraction of the ECAPs that occurs when both the working and reference electrode are on the same epidural array (Verma et al, 2023). However, using a reference as close as possible to the working electrode will increase the similarity of stimulation artifact and EMG bleed-through, and improve subsequent common mode rejection (Verma et al, 2023).…”

“…A reference was placed in adipose tissue near the spinal cord to avoid differential subtraction of the ECAPs that occurs when both the working and reference electrode are on the same epidural array (Verma et al, 2023). However, using a reference as close as possible to the working electrode will increase the similarity of stimulation artifact and EMG bleed-through, and improve subsequent common mode rejection (Verma et al, 2023). This may have exacerbated the appearance of EMG bleed-through and stimulation artifact, but based on previous studies by our group this effect is relatively minimal (Verma et al, 2023).…”

“…However, using a reference as close as possible to the working electrode will increase the similarity of stimulation artifact and EMG bleed-through, and improve subsequent common mode rejection (Verma et al, 2023). This may have exacerbated the appearance of EMG bleed-through and stimulation artifact, but based on previous studies by our group this effect is relatively minimal (Verma et al, 2023).…”

Peak Slope Ratio of the Recruitment Curves Compared to Muscle Evoked Potentials to Optimize Standing Configurations with Percutaneous Epidural Stimulation after Spinal Cord Injury

“…The introduction of spinal cord epidural stimulation (SCES) began to alter these medical beliefs and facilitated motor recovery after SCI. Over the last decade, several reports have demonstrated the use of SCES to spatiotemporally activate the lumbosacral neural circuitries and restore motor recovery [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. The use of SCES facilitates the integration of supraspinal, interspinal, and propriospinal afferent signals to generate motor behavior.…”