Electrode Array Type and Its Impact on Impedance Fluctuations and Loss of Residual Hearing in Cochlear Implantation

Hypothesis/Objective:Determine variables associated with electrode impedance fluctuations and loss of residual hearing in cochlear implant (CI) recipients.Background:CI recipients with postoperative hearing preservation demonstrate superior speech perception with an electric-acoustic stimulation (EAS) device as compared with a CI-alone device. Maintaining superior speech perception over time relies on long-term hearing preservation; therefore, understanding variables that may contribute to loss of residual hearing is needed. Recent reports suggest a relationship between changes in electrode impedance and loss of residual hearing. The variables influencing this relationship have yet to be determined.Methods:Review of pediatric and adult CI cases from 2013 to 2016 who presented with preoperative residual hearing. Regression analysis was performed to evaluate effects of array type (lateral wall vs. perimodiolar), manufacturer, age at implantation, and preoperative hearing on impedance. The correlation between peak impedance change and change in low-frequency hearing was determined.Results:One hundred forty-six CI recipients presented with preoperative residual hearing. A multivariate regression analysis demonstrated a statistically significant association between preoperative hearing thresholds (p=0.017), device manufacturer (p=0.011), and array type (p=0.038) on postoperative impedance changes. Hearing preservation rates and change in impedance differed by electrode array type. The association between peak impedance changes and loss of residual hearing differed between manufacturers (R-2=0.208, p=0.029 vs. R-2=0.016, p=0.609).Conclusion:Impedance fluctuation appears to be a marker for loss of residual hearing for specific electrode array types and manufacturers. Specific arrays may affect the cochlear microenvironment differently, with different effects on postoperative hearing preservation.