Regional Impedance Patterns in Cochlear Implantation: Influence of Demographic and Early Activation

To evaluate the effects of age and gender on electrode impedance during cochlear implant surgery and at 6 months after implantation, and to determine whether activation timing modifies these relationships across cochlear regions.

This retrospective longitudinal cohort study included cochlear implant recipients with normal cochlea implanted with the MED-EL FLEX28. All electrodes were fully inserted via the round window approach. Participants underwent early activation (1 day postoperatively) or classical activation (within approximately 1 month). Electrode impedance was measured intraoperatively and at ≥ 6 months. Associations between age, gender, activation timing, and impedance were analyzed across apical, middle, basal, and overall regions.

A total of 360 implanted ears were analyzed. Gender was not significantly associated with impedance. Implantation age demonstrated region-specific associations with impedance behavior, with the strongest findings observed in activation-stratified analyses of the apical electrodes. Mean apical impedance increased from 6.1 ± 2.1 kΩ intraoperatively to 6.9 ± 1.8 kΩ at 6 months. Younger recipients exhibited higher intraoperative apical impedance with a negative age-impedance association (β ≈ -0.01 to -0.02 per year, p < 0.001), which reversed at 6 months to a positive association (β ≈ +0.03 to +0.05 per year, p < 0.001). Age-related associations were less pronounced in the middle and basal regions.

Implantation age demonstrated a dynamic and region-specific association with impedance behavior, particularly in apical electrodes. Early activation modified postoperative impedance trajectories and attenuated midterm impedance elevation.

Level 3.