Percutaneous Placement of Bilateral Hypoglossal Nerve Stimulator Using Novel Directional Stimulating Introducer With Limited Image Guidance in Ovine Study

Abstract RATIONALE Hypoglossal nerve stimulation (HNS) is an effective treatment for obstructive sleep apnea (OSA) Current HNS therapies require surgical access and dissection of the hypoglossal nerve's (HGN) trunk to separate protrusor from retrusor and C1 branches. Dissection at the nerve trunk is technically challenging, and potentially prohibitive to perform without open visualization using a percutaneous approach. While percutaneous fine-wire HNS has been demonstrated intraoperatively, current percutaneous approaches have difficulties (1) reliably capturing the nerve due to small stimulation volume, and (2) selectively obtaining on-target protrusion without off-target retrusion. This study evaluates a new directional percutaneous introducer tool capable of identifying the optimal stimulation direction for maximum net forward protrusion. The tool is then used to deploy a wide-field self-expanding electrode array. METHODS All sheep had intraoral EMG leads placed on the genioglossus, stylohyoglossus, and submental muscles. The HGN was identified via ultrasound, and a directional introducer was inserted through a small incision. The introducer's directional stimulation field was then activated and advanced toward the HGN, with real-time EMG and tongue movement monitoring. Once genioglossus EMG was observed, the introducer was rotated through four positions (0º, 90º, 180º, and 270º) to identify the angle for optimum net forward tongue protrusion. A wide-field directional lead was inserted and deployed at the optimal direction to provide a wide-field and programmable capture of net forward protrusion. RESULTS In six insertions across four sheep, net tongue protrusion was achieved in all cases (6/6) using the directional introducer. In one case, two stimulation angles (180º and 270º) produced strong protrusor EMG with minimal retrusor activation, while angles 0º and 90º showed simultaneous protrusor and retrusor recruitment. Observations confirmed that greater protrusor EMG resulted in strong tongue protrusion, whereas balanced EMG led to slight retrusion. When a non-directional 360º stimulation field was applied, EMG indicated net retrusion, sometimes displaying a bimodal response (initial protrusion followed by retraction and ventroflexion). After determining the optimal protrusion direction in each case, a wide-field directional lead was successfully deployed at the noted optimal direction angle. Each lead was subsequently tested and through EMG and tongue observations, protrusion confirmed during stimulation. CONCLUSION This study is the first to demonstrate a percutaneous introducer that identifies the HGN's protrusor branches through directional stimulation and deploys a wide-field paddle lead to induce tongue protrusion. These findings highlight the potential for directional stimulation tools in enabling in-office procedures and therapy screenings for treating OSA with HNS.