Closed-loop SCS and sensing: now and in the future

Spinal cord stimulation (SCS) for chronic pain has undergone many advancements over the years, including the introduction of novel stimulation waveforms, expansion to treat new pain conditions, and the more recent implementation of evoked compound action potential (ECAP) controlled, closed-loop (CL) SCS. The ECAP-a measure of neural activation-may be used as a biosignal for adjusting stimulation amplitudes to avoid under- and overstimulation associated with spinal cord movement relative to the SCS lead.

Using ECAPs in a CL system relies on successfully isolating the neural response signal from the relatively large stimulation artifact. A study with the first commercialized CL-SCS device investigated pain relief with low-frequency stimulation within a therapy window described as ranging from initial perception of sensation to discomfort (paresthesia window). In contrast, another commercial system with CL technology includes additional functionality to support consistent therapy with higher frequency stimulation set at or near the perception threshold. This more recently approved CL-SCS system leverages advanced artifact suppression and flexible CL control algorithms to afford dose control for conventional, high-frequency (up to 1200 Hz), and contemporary SCS waveforms.

Here, we discuss the history and motivation for CL systems in SCS and the challenges faced when implementing such technology.