Sensing in Sacral Neuromodulation: Objective, Individualized Stimulation Response Thresholds Directly From the Lead

OBJECTIVES: Sacral neuromodulation (SNM) therapy today relies on visually observed motor responses (e.g., anal bellows contraction, toe flexion) and subjective patient feedback (pelvic region sensations) to optimize lead placement and perform device programming. Measures of sacral nerve activation used in current practice include motor and sensory thresholds, described as the stimulation amplitudes associated with first observed or reported stimulation responses. This study evaluated the utility of sacral evoked responses (SERs), recorded directly from implanted commercial SNM leads, as objective indicators of sacral nerve activation. MATERIALS AND METHODS: The PEER 2 Cohort 1 study was a multi-center, prospective, clinical feasibility study in female overactive bladder patients undergoing a tined lead evaluation for SNM using InterStim™ SureScan™ MRI leads. An investigational external neurostimulator was used to collect electrophysiological signal recordings directly from the implanted lead (SER recordings), in addition to motor and sensory thresholds at three timepoints: intraoperatively (OR), immediately postoperatively (PO), and at the end of therapy evaluation (Trial End). SER recordings were processed to determine stimulation amplitudes associated with first detectable signal (SER threshold, SERT) and analyzed for comparison with the motor and sensory thresholds. RESULTS: Lead-recorded SERs were reliably detected across subjects and timepoints: OR: 100% (89/89 subjects); PO 98.9% (87/88 subjects); Trial End: 97.7% (86/88 subjects). SERTs demonstrated statistically significant correlation with both motor and sensory thresholds across six bipolar electrode configurations (R = 0.46-0.92; p < 0.001). Compared to sensory thresholds, SERTs were a more sensitive measure of sacral nerve activation, detected at or below sensory thresholds in 57%-84% of subjects. SERTs also exhibited less variability across repeated measurements compared to sensory thresholds (p < 0.001). Replicate SERTs showed no change in 55.9% of subjects, whereas sensory thresholds showed no change in only 20.6% of subjects. CONCLUSIONS: The study results demonstrate that SERs recorded from SNM leads are reliably detected, clinically relevant, sensitive, and consistent markers of sacral nerve activation, offering an objective alternative to present-day subjective measures. Integrating lead-sensed SERs may streamline SNM programming and lead placement, introducing a simplified and standardized measure for optimizing and delivering patient-specific SNM therapy. CLINICAL TRIAL REGISTRATION: ClinicalTrials.gov NCT05200923. Investigational device. Limited by Federal (U.S.) law to investigational use. The research system and sensing feature are not approved by the FDA or any other regulatory authority and are not for sale in the US or internationally.