Long-Term Impedance Trends Over 10 Years Following Cochlear Implantation: A Retrospective Comparative Analysis

ImportanceImpedance monitoring is a critical component of cochlear implant (CI) surgery, yet the lack of comprehensive longitudinal data limits the development of evidence-based postoperative monitoring guidelines, potentially compromising patient outcomes.ObjectiveTo track impedance trends over 10 years post-implantation, evaluate the effects of electrode design on impedance dynamics, and examine the influence of patient age on impedance behavior.DesignRetrospective cohort study.SettingTertiary medical center.ParticipantsA total of 554 ears underwent cochlear implantation between June 2006 and December 2014; each ear received 1 electrode array from 1 of 6 electrode types.Exposure or InterventionLongitudinal impedance data were analyzed across apical, medial, and basal electrode contacts at 7 time points.Main Outcome MeasuresImpedance trajectories varied by age group, electrode design, and cochlear region, with persistent changes observed up to 10 years.ResultsImpedance increased markedly from intraoperative to first activation in most arrays, although a significant decrease in apical contacts was observed in CI512 adults (P = .0008). Apical and medial contacts generally stabilized or declined thereafter. In contrast, basal electrodes exhibited more heterogeneous patterns, including increases during 12 to 60 months of follow-up and decreases during 60 to 120 months. Compared to PM arrays, LW electrodes showed higher apical impedances, medial impedances that were mostly comparable and time-dependent, and persistently lower basal impedances than CI512. Among LW arrays, CI422 consistently demonstrated the highest impedance, whereas the MED-EL electrode series, Flexsoft exhibited the highest impedance. Overall impedances were higher in early childhood recipients, while adults tended to show higher values in the basal region.ConclusionThis study provides the first decade-long characterization of impedance changes, revealing dynamic variations in electrode impedance across different designs and age groups of cochlear implant recipients.RelevanceThis study highlights the need for long-term monitoring and offering practical guidance for individualized programming and electrode design.