Cochlear Implant Electrode Impedance as Potential Biomarker for Residual Hearing

Abstract

Introduction and ObjectivesAmong cochlear implant candidates, an increasing number of patients are presenting with residual acoustic hearing. To monitor the postoperative course of structural and functional preservation of the cochlea, a reliable objective biomarker would be desirable. Recently, impedance telemetry has gained increasing attention in this field. The aim of this study was to investigate the postoperative course of the residual acoustic hearing and clinical impedance in patients with long electrode arrays and to explore the applicability of impedance telemetry for monitoring residual hearing.MethodsWe retrospectively analyzed records of 42 cochlear implant recipients with residual hearing covering a median postoperative follow-up of 25 months with repeated simultaneous pure tone audiometry and impedance telemetry. We used a linear mixed-effects model to estimate the relation between clinical electrode impedance and residual hearing. Besides the clinical impedance, the follow-up time, side of implantation, gender, and age at implantation were included as fixed effects. An interaction term between impedance and follow-up time, as well as subject-level random intercepts and slopes, were included.ResultsLoss of residual hearing occurred either during surgery or within the first 6 post-operative months. Electrode contacts inserted further apically (i.e., deeper) had higher impedances, independent of residual hearing. The highest impedances were measured 1 month postoperatively and gradually decreased over time. Basal electrodes were more likely to maintain higher impedance. Follow-up time was significantly associated with residual hearing. Regardless of the time, we found that a 1 kΩ increase in clinical impedance was associated with a 4.4 dB deterioration of residual hearing (p < 0.001).ConclusionPure tone audiometry is the current gold standard for monitoring postoperative residual hearing. However, the association of clinical impedances with residual hearing thresholds found in our study could potentially be exploited for objective monitoring using impedance telemetry. Further analysis including near-field related impedance components could be performed for improved specificity to local immune responses.

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“…Previous studies have published mixed results regarding the link between impedances and electrode positioning. For example, some studies reported higher impedances at the apex of the cochlea compared to the base ( 25 , 26 , 28 ), while Saunders et al ( 27 ) reported an inverse relationship. Studies that linked impedance measurements to electrode-to-modiolus distance did not find a clear relationship ( 22 , 27 , 28 ).…”

“…Therefore, it might indicate variations in the tissues surrounding the electrode and its resistive properties. Some studies have reported higher impedances for apical contacts than basal contacts ( 25 , 26 ), while others found an inverse relationship ( 27 ). No clear relationship is found between impedances and distance to the modiolus ( 28 ).…”

Cochlear Implantation Following Transcanal Infrapromontorial Approach for Vestibular Schwannoma: A Case Series

“…Wimmer and colleagues observed higher impedances measured one month after surgery and their gradual decrement over time. Electrode contacts inserted more apically exhibited higher impedances, but basal electrodes maintained higher impedance for longer [ 26 ]. A similar trend was recorded in this study in patients No.…”

“…3. The former was not uncommon in the postoperative period and already described as related to inner ear events leading to a loss of residual hearing and dizziness [ 26 ]. The second could be related to possible dilatation or scar tissue formation due to the removal of the posterior part of the cochlear basal turn.…”

An intracochlear electrocochleography dataset - from raw data to objective analysis using deep learning

“…ECochG can also be useful in the post-operative phase, where patients may lose residual cochlear function 21,22 . Most commonly, such losses occur during the first six to twelve months after implant surgery [23][24][25] due to different intra-cochlear factors (e.g., immune response to the electrode, intracochlear inflammatory reactions, and intracochlear scar tissue formation) 14,26,27 . However, the underlying mechanisms remain poorly understood and require further research 24 .…”