Cochlear Implantation: Long-Term Effect of Early Activation on Electrode Impedance

Abstract

Objectives: The growing adoption of cochlear implants (CIs) necessitates understanding the factors influencing long-term performance and improved outcomes. This work investigated the long-term effect of early activation of CIs on electrode impedance in a large sample of CI users at different time points. Methods: A retrospective study on 915 ears from CI patients who were implanted between 2015 and 2020. According to their CI audio processor activation time, the patients were categorized into early activation (activated 1 day after surgery, n = 481) and classical activation (activated 4 weeks after surgery, n = 434) groups. Then, the impact of the activation times on the electrode impedance values, along the electrode array contacts, at different time points up to two years was studied and analyzed. Results: The early activation group demonstrated lower impedance values across all the electrode array sections compared to the classical activation at 1 month, 1 year, and 2 years post-implantation. At 1 month, early activation was associated with a reduction of 0.34 kΩ, 0.46 kΩ, and 0.37 kΩ in the apical, middle, and basal sections, respectively. These differences persisted at subsequent intervals. Conclusions: Early activation leads to sustained reductions in the electrode impedance compared to classical activation (CA), suggesting that earlier activation might positively affect long-term CI outcomes.

Keywords: classical activation; cochlear implant; early activation; electrode impedance; green cochlea; post-op outcomes; sustainability.

Figure 1

Shows the density plots for each research group’s electrode impedance at various electrode sections and time intervals. The following examples illustrate the skewed distributions: (a) the apical electrode impedance values at different times in both groups, (b) the middle electrode impedance values at different times in both groups, (c) the basal electrode impedance values at different times in both groups and (d) the overall electrode impedance values at different times in both groups.

Figure 1

Shows the density plots for each research group’s electrode impedance at various electrode sections and time intervals. The following examples illustrate the skewed distributions: (a) the apical electrode impedance values at different times in both groups, (b) the middle electrode impedance values at different times in both groups, (c) the basal electrode impedance values at different times in both groups and (d) the overall electrode impedance values at different times in both groups.

Figure 2

Dumbbell chart of the difference in the median electrode impedance between the study groups at each electrode section at each interval post-implantation. Each pair of points adjacent to the same time point shows the corresponding medians of both groups and is connected by a black horizontal line representing the difference: (a) for the apical electrode section, (b) for the middle electrode section, (c) for the basal electrode section, and (d) for the overall electrode.

Figure 3

Boxplots showing the electrode impedance variations at different electrode sections over time after implantation within the EA and CA groups: (a) for the apical electrode section, (b) for the middle electrode section, (c) for the basal electrode section, and (d) for the overall electrode. ns = non-significant, p ≤ 0.05 is indicated *, p ≤ 0.01 by **, and p ≤ 0.0001 by ****.