Spatiotemporal Dynamics of Cochlear Implant Electrode Impedance in Standard and Dexamethasone-Eluting Electrode Arrays

Objective: To evaluate the spatiotemporal dynamics of cochlear implant electrode impedance in standard and dexamethasone-eluting electrode arrays (Dex-EA). Study design: Prospective, double-arm study. Setting: Single tertiary referral center. Patients: Thirty-one (17 control and 14 experimental) subjects meeting Food and Drug Administration criteria for cochlear implantation. Interventions: Standard-of-care cochlear implant with intraoperative postinsertion impedance measurement. Main outcome measures: Daily impedance measurements for a targeted 90 days postinitial activation. Results: This study demonstrates the spatiotemporal dynamics of electrode impedance observed over the first 90 days postimplantation with standard EAs, and the effects of Dex-EAs on these dynamics. For the control group, impedances for the 12 basal electrodes (1 to 12) increase over time while they decrease for the 10 apical electrodes (13 to 22). In comparison, not only do Dex-EAs result in smaller impedance values across all 22 electrodes over the first 90 days after initial activation, but the impedances also tend to decrease over time at all electrode locations. There is a statistically significant difference in impedance between the 2 cohorts at every electrode (P<0.0001), but the difference is largest for the basal electrodes. Dex-EAs also result in lower within-subject variability across repeated impedance measures over this short time window. Conclusions: Dex-EAs result in smaller, more stable impedance values across repeated measures over the first 90 days after initial activation as compared with commercially available standard CI electrode arrays. The dramatically lower impedances, reduced fluctuations, and resistance to rising values particularly at basal locations reflect the clinical advantages of Dex-EA toward diminishing the foreign body response and may also enhance stimulation from the CI.