Improving Therapy Adherence in Closed-loop Spinal Cord Stimulation Through a Directional Expandable Lead

Introduction: Closed-loop spinal cord stimulation (SCS) systems deliver adaptive therapy by recording evoked compound action potentials (ECAPs) and adjusting stimulation output in real time. While stimulation frequencies are comparable to open-loop SCS, the added sensing and processing burden may increase device energy consumption and impact usability. Although no published data quantify recharge frequency, it is plausible that the operational demands of closed-loop systems contribute to therapy fatigue, particularly when frequent IPG recharging or reprogramming is required. A lead that improves stimulation efficiency and ECAP sensing quality could reduce system demands and help support long-term adherence.

Methods: We evaluated a novel percutaneous expandable lead (Heron®) designed for directional stimulation and high-fidelity ECAP sensing. Heron features an 8-contact multicolumn configuration that unfolds at the target, directing current toward the dorsal columns while maintaining cylindrical-like delivery access. Assessment included:
- a computational model simulating current distribution and electric field in the spinal cord of Heron compared with a cylindrical lead at 1.0 mA;
- In vivo sheep studies comparing ECAP amplitude and stimulation thresholds;
- Bench testing of voltage transients and energy per pulse to assess electrochemical efficiency.

Results: - The computational model showed that the electric field from the Heron propagates more focal in the spinal cord (Figure 1).
- Heron required ~30% less stimulation current to evoke ECAPs of equivalent amplitude ( < 0.7 mA vs 1 mA). ECAPs recorded were significantly greater in amplitude (41.1 ± 5.2 μV vs. 28.1 ± 4.8 μV) at 1.0 mA (Figure 2) and exhibited a more pronounced amplitude increase at 1.1 mA (+27% vs. +11%).
- Voltage transient analysis showed that Heron had a 40% lower polarization voltage at 1 mA, and 51% lower at 0.7 mA. Correspondingly, Heron’s energy per pulse was reduced by 40% at equal current, and by up to 66% when accounting for its lower stimulation threshold (Figure 3).

Conclusion: The Heron lead enhances the efficiency and precision of closed-loop neuromodulation through directional stimulation, superior ECAP capture, and optimized electrochemical behavior. These combined features result in lower stimulation thresholds, reduced voltage excursions, and significantly decreased energy consumption per pulse. This may reduce IPG recharge burden and reprogramming needs, key barriers to sustained use of closed-loop systems. By improving the practicality of adaptive therapy from the patient’s perspective, Heron offers the opportunity to support long-term adherence and clinical success in ECAP-driven neuromodulation.