Spatial Analysis of Electrode Proximity to Lateral Wall and Its Impact on ECAP Amplitudes: An OTOPLAN-Based Study

BACKGROUND: Precise electrode positioning is essential for optimizing cochlear implant outcomes. However, the impact of electrode-to-lateral wall distance on neural responsiveness remains unclear. OBJECTIVE: To investigate whether electrode proximity to the lateral wall influences electrically evoked compound action potential (ECAP) amplitudes. METHODS: A retrospective cohort of 44 implanted ears with lateral wall electrodes was analyzed. High-resolution computed tomography scans were processed using OTOPLAN to measure electrode-to-lateral wall distances. Postoperative ECAPs were recorded, and correlations between distance and ECAP amplitudes were assessed at overall, channel-specific, and regional levels. RESULTS: Electrode-to-lateral wall distances ranged from 1.91 to 3.61 mm, and ECAP amplitudes from 9.93 to 16.98 μV. A significant positive correlation was found across all electrode-ear pairs (r=+0.58, P<0.001), indicating higher amplitudes with greater distances. Channel-level analysis showed a stronger association (r=+0.76, P=0.004), while regional analysis identified the middle cochlear region as the primary contributor (r=+0.34, 95% CI: 0.08-0.55). CONCLUSION: Greater electrode-to-lateral wall distances are associated with higher ECAP amplitudes, particularly in the middle cochlear region. These findings suggest that greater electrode-to-modiolar proximity, as achieved with perimodiolar arrays or cochlear morphology that positions electrodes further from the lateral wall, may enhance neural responsiveness. Electrode-to-lateral wall distance may serve as a clinically actionable spatial metric for anticipating ECAP responses and optimizing stimulation strategies in cochlear implant programming.