Evoked compound action potentials during spinal cord stimulation: effects of posture and pulse width on signal features and neural activation within the spinal cord

Abstract

Objective. Evoked compound action potential (ECAP) recordings have emerged as a quantitative measure of the neural response during spinal cord stimulation (SCS) to treat pain. However, utilization of ECAP recordings to optimize stimulation efficacy requires an understanding of the factors influencing these recordings and their relationship to the underlying neural activation.

Approach. We acquired a library of ECAP recordings from 56 patients over a wide assortment of postures and stimulation parameters, and then processed these signals to quantify several aspects of these recordings (e.g., ECAP threshold, amplitude, latency, growth rate). We compared our experimental findings against a computational model that examined the effect of variable distances between the spinal cord and the SCS electrodes.

Main results. Postural shifts strongly influenced the experimental ECAP recordings, with a 65.7% lower ECAP threshold and 178.5% higher growth rate when supine versus seated. The computational model exhibited similar trends, with a 71.9% lower ECAP threshold and 231.5% higher growth rate for a 2.0-mm cerebrospinal fluid layer (representing a supine posture) versus a 4.4-mm cerebrospinal fluid layer (representing a prone posture). Furthermore, the computational model demonstrated that constant ECAP amplitudes may not equate to a constant degree of neural activation.

Significance. These results demonstrate large variability across all ECAP metrics and the inability of a constant ECAP amplitude to provide constant neural activation. These results are critical to improve the delivery, efficacy, and robustness of clinical SCS technologies utilizing these ECAP recordings to provide closed-loop stimulation.

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

“…The measurement of evoked compound action potentials (ECAPs) during stimulation-evoked epidural spinal recordings (ESRs) have been used to elucidate fundamental mechanisms of intended therapy and limiting off-target effects, as well as to provide a marker for closed-loop control of SCS (Brucker-Hahn et al, 2023; Dinsmoor et al, 2022; Lempka & Patil, 2018; Parker et al, 2012, 2013; Russo et al, 2020). Previous studies using ECAPs to understand other neuromodulation therapies have predominantly been performed in well-controlled acute settings.…”