Intraoperative Observational Real-time Electrocochleography as a Predictor of Hearing Loss After Cochlear Implantation: 3 and 12 Month Outcomes

International Consensus Statements on Intraoperative Testing for Cochlear Implantation Surgery

OBJECTIVES

A wide variety of intraoperative tests are available in cochlear implantation. However, no consensus exists on which tests constitute the minimum necessary battery. We assembled an international panel of clinical experts to develop, refine, and vote upon a set of core consensus statements.

DESIGN

A literature review was used to identify intraoperative tests currently used in the field and draft a set of provisional statements. For statement evaluation and refinement, we used a modified Delphi consensus panel structure. Multiple interactive rounds of voting, evaluation, and feedback were conducted to achieve convergence.

RESULTS

Twenty-nine provisional statements were included in the original draft. In the first voting round, consensus was reached on 15 statements. Of the 14 statements that did not reach consensus, 12 were revised based on feedback provided by the expert practitioners, and 2 were eliminated. In the second voting round, 10 of the 12 revised statements reached a consensus. The two statements which did not achieve consensus were further revised and subjected to a third voting round. However, both statements failed to achieve consensus in the third round. In addition, during the final revision, one more statement was decided to be deleted due to overlap with another modified statement.

CONCLUSIONS

A final core set of 24 consensus statements was generated, covering wide areas of intraoperative testing during CI surgery. These statements may provide utility as evidence-based guidelines to improve quality and achieve uniformity of surgical practice.

Predicting Postoperative Speech Perception and Audiometric Thresholds Using Intracochlear Electrocochleography in Cochlear Implant Recipients

OBJECTIVES

Electrocochleography (ECochG) appears to offer the most accurate prediction of post-cochlear implant hearing outcomes. This may be related to its capacity to interrogate the health of underlying cochlear tissue. The four major components of ECochG (cochlear microphonic [CM], summating potential [SP], compound action potential [CAP], and auditory nerve neurophonic [ANN]) are generated by different cochlear tissue components. Analyzing characteristics of these components can reveal the state of hair and neural cell in a cochlea. There is limited evidence on the characteristics of intracochlear (IC) ECochG recordings measured across the array postinsertion but compared with extracochlear recordings has better signal to noise ratio and spatial specificity. The present study aimed to examine the relationship between ECochG components recorded from an IC approach and postoperative speech perception or audiometric thresholds.

DESIGN

In 113 human subjects, responses to 500 Hz tone bursts were recorded at 11 IC electrodes across a 22-electrode cochlear implant array immediately following insertion. Responses to condensation and rarefaction stimuli were then subtracted from one another to emphasize the CM and added to one another to emphasize the SP, ANN, and CAP. Maximum amplitudes and extracochlear electrode locations were recorded for each of these ECochG components. These were added stepwise to a multi-factor generalized additive model to develop a best-fit model predictive model for pure-tone audiometric thresholds (PTA) and speech perception scores (speech recognition threshold [SRT] and consonant-vowel-consonant phoneme [CVC-P]) at 3- and 12-month postoperative timepoints. This best-fit model was tested against a generalized additive model using clinical factors alone (preoperative score, age, and gender) as a null model proxy.

RESULTS

ECochG-factor models were superior to clinical factor models in predicting postoperative PTA, CVC-P, and SRT outcomes at both timepoints. Clinical factor models explained a moderate amount of PTA variance ( r2 = 45.9% at 3-month, 31.8% at 12-month, both p < 0.001) and smaller variances of CVC-P and SRT ( r2 range = 6 to 13.7%, p = 0.008 to 0.113). Age was not a significant predictive factor. ECochG models explained more variance at the 12-month timepoint ( r2 for PTA = 52.9%, CVC-P = 39.6%, SRT = 36.4%) compared with the 3-month one timepoint ( r2 for PTA = 49.4%, CVC-P = 26.5%, SRT = 22.3%). The ECochG model was based on three factors: maximum SP deflection amplitude, and electrode position of CM and SP peaks. Adding neural (ANN and/or CAP) factors to the model did not improve variance explanation. Large negative SP deflection was associated with poorer outcomes and a large positive SP deflection with better postoperative outcomes. Mid-array peaks of SP and CM were both associated with poorer outcomes.

CONCLUSIONS

Postinsertion IC-ECochG recordings across the array can explain a moderate amount of postoperative speech perception and audiometric thresholds. Maximum SP deflection and its location across the array appear to have a significant predictive value which may reflect the underlying state of cochlear health.

Amplitude Parameters Are Predictive of Hearing Preservation in a Randomized Controlled Trial of Intracochlear Electrocochleography During Cochlear Implant Surgery

OBJECTIVE

To prospectively evaluate the association between hearing preservation after cochlear implantation (CI) and intracochlear electrocochleography (ECochG) amplitude parameters.

STUDY DESIGN

Multi-institutional, prospective randomized clinical trial.

SETTING

Ten high-volume, tertiary care CI centers.

PATIENTS

Adults (n = 87) with sensorineural hearing loss meeting CI criteria (2018-2021) with audiometric thresholds of ≤80 dB HL at 500 Hz.

METHODS

Participants were randomized to CI surgery with or without audible ECochG monitoring. Electrode arrays were inserted to the full-depth marker. Hearing preservation was determined by comparing pre-CI, unaided low-frequency (125-, 250-, and 500-Hz) pure-tone average (LF-PTA) to LF-PTA at CI activation. Three ECochG amplitude parameters were analyzed: 1) insertion track patterns, 2) magnitude of ECochG amplitude change, and 3) total number of ECochG amplitude drops.

RESULTS

The Type CC insertion track pattern, representing corrected drops in ECochG amplitude, was seen in 76% of cases with ECochG "on," compared with 24% of cases with ECochG "off" ( p = 0.003). The magnitude of ECochG signal drop was significantly correlated with the amount of LF-PTA change pre-CI and post-CI ( p < 0.05). The mean number of amplitude drops during electrode insertion was significantly correlated with change in LF-PTA at activation and 3 months post-CI ( p ≤ 0.01).

CONCLUSIONS

ECochG amplitude parameters during CI surgery have important prognostic utility. Higher incidence of Type CC in ECochG "on" suggests that monitoring may be useful for surgeons in order to recover the ECochG signal and preventing potentially traumatic electrode-cochlear interactions.

ZH-ECochG Bode Plot: A Novel Approach to Visualize Electrocochleographic Data in Cochlear Implant Users

Background: Various representations exist in the literature to visualize electrocochleography (ECochG) recordings along the basilar membrane (BM). This lack of generalization complicates comparisons within and between cochlear implant (CI) users, as well as between publications. This study synthesized the visual representations available in the literature via a systematic review and provides a novel approach to visualize ECochG data in CI users. Methods: A systematic review was conducted within PubMed and EMBASE to evaluate studies investigating ECochG and CI. Figures that visualized ECochG responses were selected and analyzed. A novel visualization of individual ECochG data, the ZH-ECochG Bode plot (ZH = Zurich), was devised, and the recordings from three CI recipients were used to demonstrate and assess the new framework. Results: Within the database search, 74 articles with a total of 115 figures met the inclusion criteria. Analysis revealed various types of representations using different axes; their advantages were incorporated into the novel visualization framework. The ZH-ECochG Bode plot visualizes the amplitude and phase of the ECochG recordings along the different tonotopic regions and angular insertion depths of the recording sites. The graph includes the pre- and postoperative audiograms to enable a comparison of ECochG responses with the audiometric profile, and allows different measurements to be shown in the same graph. Conclusions: The ZH-ECochG Bode plot provides a generalized visual representation of ECochG data, using well-defined axes. This will facilitate the investigation of the complex ECochG potentials generated along the BM and allows for better comparisons of ECochG recordings within and among CI users and publications. The scripts used to construct the ZH-ECochG Bode plot are provided by the authors.

Two different methods to digitally visualize continuous electrocochleography potentials during cochlear implantation: a first description of feasibility

PURPOSE

The study explores the potential of real-time electrocochleographic potentials (ECochG) visualization during electrode insertion using digital microscopes such as RoboticScope (BHS®). Collaborative software development of the MAESTRO Software (MED-EL®) offers continuous ECochG monitoring during implantation and postoperative hearing evaluation, addressing previous time constraints. The study aims to assess software applicability and the impact of real-time visualization on long-term residual hearing preservation.

METHODS

Eight patients with residual hearing underwent cochlear implantation with Flex26 or Flex28 electrode according to the Otoplan evaluation. ECochG responses were measured and visualized during electrode insertion, with insertion times recorded. Two randomized display methods (graph and arrows) tracked ECochG potentials. Postoperative behavioral thresholds determined hearing preservation. Successful real-time intraoperative ECochG visualization was achieved in all cases, enabling surgeon adaptation. Mean electrode insertion time was 114 s, with postoperative thresholds comparable to preoperative values. Visualization did not affect surgeon workload. ECochG amplitudes differed between patients with and without residual hearing.

CONCLUSION

The study demonstrates effective implementation of advanced ECochG software combined with real-time visualization, enabling residual hearing preservation during CI. Visualization had no apparent effect on surgeon performance or workload. Future investigation involving a larger population will assess the long-term impact of ECochG on hearing threshold and structure preservation.

Four-Point Impedance: A Potential Biomarker for Residual Hearing After Cochlear Implantation

INTRODUCTION

Preservation of residual hearing after cochlear implantation allows for electroacoustic stimulation, which leads to better music appreciation, noise localization, and speech comprehension in noisy environments. Real-time intraoperative electrocochleography (rt-ECochG) monitoring has shown promise in improving residual hearing rates. Four-point impedance (4PI) is being explored as a potential biomarker in cochlear implantation that has been associated with fibrotic tissue response, hearing loss, and dizziness. In this study, we explore whether monitoring both rt-ECochG intraoperatively and postoperative 4PI improves predictions of the preservation of residual hearing.

METHODS

This was a prospective cohort study. Adults with residual acoustic hearing underwent cochlear implantation with intraoperative intracochlear electrocochleography (ECochG) monitoring. The surgeon responded to a drop in ECochG signal amplitude of greater than 30% by a standardized manipulation of the electrode with the aim of restoring the ECochG. At the end of the procedure, the ECochG signal was categorized as being maintained or having dropped more than 30%. 4PI was measured on 1 day, 1 week, and 1 and 3 months after cochlear implantation. Residual hearing was measured by routine pure-tone audiogram at 3 months postoperatively. The ECochG category and 4PI impedance values were entered as factors in a multiple linear regression predicting the protection of residual hearing.

RESULTS

Twenty-six patients were recruited. Rt-ECochG significantly predicted residual hearing at 3 months (t test; mean difference, 37.7%; p = 0.002). Inclusion of both 1-day or 3-month 4PI in a multiple linear regression with rt-ECochG markedly improved upon correlations with residual hearing compared with the rt-ECochG-only model (rt-ECochG and 1-d 4PI model, R2 = 0.67; rt-ECochG and 3-mo 4PI model, R2 = 0.72; rt-ECochG-only model, R2 = 0.33).

CONCLUSIONS

Both rt-ECochG and 4PI predict preservation of residual hearing after cochlear implantation. These findings suggest that the biological response of the cochlea to implantation, as reflected in 4PI, is an important determinant of residual hearing, independent of the acute effects on hearing during implant surgery seen with rt-ECochG. We speculate that 4PI relates to inflammation 1 day after implantation and fibrosis at 3 months.

Digital live imaging of intraoperative electrocochleography during cochlear implantation: the first 50 patients

INTRODUCTION

Real-time visualization of intraoperative electrocochleography (ECochG) potentials via a digital microscope during cochlear implantation can provide direct feedback during electrode insertion. The aim of this prospective, randomized study of 50 patients was to obtain long-term data with a focus on residual hearing preservation and speech understanding.

MATERIAL AND METHODS

Cochlear implantations were performed in 50 patients (26 female, 24 male) with residual hearing using a digital microscope. Patients were randomized into two groups. Intraoperative ECochG potentials were either displayed directly in the surgeon's field of view (picture-in-picture display, PiP) or not directly in the field of view (without picture-in-picture display, without PiP). Residual hearing preservation and speech comprehension were recorded within a 1-year follow-up period, compared between groups (PiP versus without PiP) and to a control group of 26 patients implanted without ECochG.

RESULTS

Mean insertion time was significantly longer in the picture-in-picture group (p = 0.025). Residual hearing preservation after 6 weeks at 250 Hz was significantly better in the picture-in-picture group (p = 0.017). After one year, 76% of patients showed residual hearing in the picture-in-picture group (62% without picture-in-picture technique, p = n.s.). Use of the picture-in-picture technique resulted in better long-term pure tone residual hearing preservation at 250, 500, and 1000 Hz. Speech intelligibility improved by 46% in the picture-in-picture group (38% without picture-in-picture).

DISCUSSION

This study is the first to describe long-term results in a large cohort of cochlear implant patients in whom digital visualization of intraoperative ECochG was used. Our results show that visualization of intraoperative ECochG has a positive effect on residual hearing preservation.

Combining Intraoperative Electrocochleography with Robotics-Assisted Electrode Array Insertion

OBJECTIVE

To describe the use of robotics-assisted electrode array (EA) insertion combined with intraoperative electrocochleography (ECochG) in hearing preservation cochlear implant surgery.

STUDY DESIGN

Prospective, single-arm, open-label study.

SETTING

All procedures and data collection were performed at a single tertiary referral center.

PATIENTS

Twenty-one postlingually deaf adult subjects meeting Food and Drug Administration indication criteria for cochlear implantation with residual acoustic hearing defined as thresholds no worse than 65 dB at 125, 250, and 500 Hz.

INTERVENTION

All patients underwent standard-of-care unilateral cochlear implant surgery using a single-use robotics-assisted EA insertion device and concurrent intraoperative ECochG.

MAIN OUTCOME MEASURES

Postoperative pure-tone average over 125, 250, and 500 Hz measured at initial activation and subsequent intervals up to 1 year afterward.

RESULTS

Twenty-two EAs were implanted with a single-use robotics-assisted insertion device and simultaneous intraoperative ECochG. Fine control over robotic insertion kinetics could be applied in response to changes in ECochG signal. Patients had stable pure-tone averages after activation with normal impedance and neural telemetry responses.

CONCLUSIONS

Combining robotics-assisted EA insertion with intraoperative ECochG is a feasible technique when performing hearing preservation implant surgery. This combined approach may provide the surgeon a means to overcome the limitations of manual insertion and respond to cochlear feedback in real-time.

Intracochlear Recording of Electrocochleography During and After Cochlear Implant Insertion Dependent on the Location in the Cochlea

To preserve residual hearing during cochlear implant (CI) surgery it is desirable to use intraoperative monitoring of inner ear function (cochlear monitoring). A promising method is electrocochleography (ECochG). Within this project the relations between intracochlear ECochG recordings, position of the recording contact in the cochlea with respect to anatomy and frequency and preservation of residual hearing were investigated. The aim was to better understand the changes in ECochG signals and whether these are due to the electrode position in the cochlea or to trauma generated during insertion. During and after insertion of hearing preservation electrodes, intraoperative ECochG recordings were performed using the CI electrode (MED-EL). During insertion, the recordings were performed at discrete insertion steps on electrode contact 1. After insertion as well as postoperatively the recordings were performed at different electrode contacts. The electrode location in the cochlea during insertion was estimated by mathematical models using preoperative clinical imaging, the postoperative location was measured using postoperative clinical imaging. The recordings were analyzed from six adult CI recipients. In the four patients with good residual hearing in the low frequencies the signal amplitude rose with largest amplitudes being recorded closest to the generators of the stimulation frequency, while in both cases with severe pantonal hearing losses the amplitude initially rose and then dropped. This might be due to various reasons as discussed in the following. Our results indicate that this approach can provide valuable information for the interpretation of intracochlearly recorded ECochG signals.

Intraoperative Measured Electrocochleography and Fluoroscopy Video to Detect Cochlea Trauma

HYPOTHESIS

Gross electrode movements detected with intraoperative, real-time X-ray fluoroscopy will correlate with fluctuations in cochlear output, as measured with intraoperative electrocochleography (ECochG).

BACKGROUND

Indications for cochlear implantation (CI) are expanding to include patients with residual hearing; however, implant recipients often lose residual hearing after CI. The objective of this study was to identify probable traumatic events during implantation by combining electrophysiological monitoring of cochlear function with simultaneous X-ray monitoring. The surgical timing of these apparently traumatic events was then investigated.

METHODS

For 19 adult patients (21 surgeries, 2 bilateral), the ECochG responses were measured during implantation of a cochlear nucleus slim modiolar electrode (CI532/CI632, Cochlear Ltd Australia Nucleus slim modiolar). Simultaneous fluoroscopy was performed, as well as a postoperative cone-beam computed tomography (CT) scan. For all patients, pre- and postoperative audiograms were recorded up to 1 year after surgery to record the loss of residual hearing.

RESULTS

Electrode insertions for 21 surgeries were successfully monitored. A drop in ECochG response was significantly correlated with reduced hearing preservation compared with patients with preserved responses throughout. Drops in the ECochG response were measured to occur during insertion, because of movement of the array after insertion was complete, including while sealing of the electrode array at the round window or coiling of the array lead within the mastoid cavity. In some patients, a reduction in cochlear output, resulting in poor ECochG response, was inferred to occur before the beginning of implantation.

CONCLUSION

The combination of perioperative ECochG measurements, microscope video, fluoroscopy, and postoperative CT scan may inform on what causes the loss of residual hearing after implantation. These findings will be used to improve the surgical procedure in future.

A Multicenter Comparison of 1-yr Functional Outcomes and Programming Differences Between the Advanced Bionics Mid-Scala and SlimJ Electrode Arrays

OBJECTIVE

To determine if there is a difference in hearing outcomes or stimulation levels between Advanced Bionics straight and precurved arrays.

STUDY DESIGN

Retrospective chart review across three implant centers.

SETTING

Tertiary centers for cochlear and auditory brainstem implantation.

PATIENTS

One hundred fifteen pediatric and 205 adult cochlear implants (CIs) were reviewed. All patients were implanted under the National Institute for Health and Care Excellence 2009 guidelines with a HiRes Ultra SlimJ or Mid-Scala electrode array.

MAIN OUTCOME MEASURES

Hearing preservation after implantation, as well as CI-only listening scores for Bamford-Kowal-Bench sentences were compared 1 year after implantation. Stimulation levels for threshold and comfort levels were also compared 1 year after implantation.

RESULTS

Hearing preservation was significantly better with the SlimJ compared with the Mid-Scala electrode array. Bamford-Kowal-Bench outcomes were not significantly different between the two arrays in any listening condition. Stimulation levels were not different between arrays but did vary across electrode contacts. At least one electrode was deactivated in 33% of implants but was more common for the SlimJ device.

CONCLUSION

Modern straight and precurved arrays from Advanced Bionics did not differ in hearing performance or current requirements. Although hearing preservation was possible with both devices, the SlimJ array would still be the preferred electrode in cases where hearing preservation was a priority. Unfortunately, the SlimJ device was also prone to poor sound perception on basal electrodes. Further investigation is needed to determine if deactivated electrodes are associated with electrode position/migration, and if programming changes are needed to optimize the use of these high-frequency channels.

Evaluation of Real-Time Intracochlear Electrocochleography for Guiding Cochlear Implant Electrode Array Position

This study evaluates intracochlear electrocochleography (ECochG) for real-time monitoring during cochlear implantation. One aim tested whether adjusting the recording electrode site would help differentiate between atraumatic and traumatic ECochG amplitude decrements. A second aim assessed whether associations between ECochG amplitude decrements and post-operative hearing loss were weaker when considering hearing sensitivity at the ECochG stimulus frequency compared to a broader frequency range. Eleven adult cochlear implant recipients who were candidates for electro-acoustic stimulation participated. Single-frequency (500-Hz) ECochG was performed during cochlear implantation; the amplitude of the first harmonic of the difference waveform was considered. Post-operative hearing preservation at 500 Hz ranged from 0 to 94%. The expected relationship between ECochG amplitude decrements and hearing preservation was observed, though the trend was not statistically significant, and predictions were grossly inaccurate for two participants. Associations did not improve when considering alternative recording sites or hearing sensitivity two octaves above the ECochG stimulus frequency. Intracochlear location of a moving recording electrode is a known confound to real-time interpretation of ECochG amplitude fluctuations, which was illustrated by the strength of the correlation with ECochG amplitude decrements. Multiple factors contribute to ECochG amplitude patterns and to hearing preservation; these results highlight the confounding influence of intracochlear recording electrode location on the ECochG.

Characteristics of the Summating Potential Measured Across a Cochlear Implant Array as an Indicator of Cochlear Function

OBJECTIVES

The underlying state of cochlear and neural tissue function is known to affect postoperative speech perception following cochlear implantation. The ability to assess these tissues in patients can be performed using intracochlear electrocochleography (IC ECochG). One component of ECochG is the summating potential (SP) that appears to be generated by multiple cochlear tissues. Its qualities may be able to detect the presence of functional inner hair cells, but evidence for this is limited in human cochleae. This study aimed to examine the IC SP characteristics in cochlear implantation recipients, its relationship to preoperative speech perception and audiometric thresholds, and to other IC ECochG components.

DESIGN

This is a retrospective analysis of 113 patients' IC ECochG recordings across the array in response to a 500 Hz tone burst stimulus. Responses to condensation and rarefaction stimuli were then subtracted from one another to emphasize the cochlear microphonic and added to one another to emphasize the SP, auditory nerve neurophonic, and compound action potential. Patients were grouped based on their maximum SP deflection being large and positive (+SP), large and negative (-SP), or minimal (0 SP) to further investigate these relationships.

RESULTS

Patients in the +SP group had better preoperative speech perception (mean consonant-vowel-consonant phoneme score 46%) compared to the -SP and 0 SP groups (consonant-vowel-consonant phoneme scores 34% and 36%, respectively, difference to +SP: p < 0.05). Audiometric thresholds were lowest for +SP (mean pure-tone average 50 dB HL), then -SP (65 dB HL), and highest for 0 SP patients (70 dB HL), but there was not a statistical significance between +SP and -SP groups ( p > 0.1). There were also distinct differences between SP groups in the qualities of their other ECochG components. These included the +SP patients having larger cochlear microphonic maximum amplitude, more apical SP peak electrode locations, and a more spatially specific SP magnitude growth pattern across the array.

CONCLUSIONS

Patients with large positive SP deflection in IC ECochG have preoperatively better speech perception and lower audiometric thresholds than those without. Patterns in other ECochG components suggest its positive deflection may be an indicator of cochlear function.

Assessment of cochlear synaptopathy by electrocochleography to low frequencies in a preclinical model and human subjects

Cochlear synaptopathy is the loss of synapses between the inner hair cells and the auditory nerve despite survival of sensory hair cells. The findings of extensive cochlear synaptopathy in animals after moderate noise exposures challenged the long-held view that hair cells are the cochlear elements most sensitive to insults that lead to hearing loss. However, cochlear synaptopathy has been difficult to identify in humans. We applied novel algorithms to determine hair cell and neural contributions to electrocochleographic (ECochG) recordings from the round window of animal and human subjects. Gerbils with normal hearing provided training and test sets for a deep learning algorithm to detect the presence of neural responses to low frequency sounds, and an analytic model was used to quantify the proportion of neural and hair cell contributions to the ECochG response. The capacity to detect cochlear synaptopathy was validated in normal hearing and noise-exposed animals by using neurotoxins to reduce or eliminate the neural contributions. When the analytical methods were applied to human surgical subjects with access to the round window, the neural contribution resembled the partial cochlear synaptopathy present after neurotoxin application in animals. This result demonstrates the presence of viable hair cells not connected to auditory nerve fibers in human subjects with substantial hearing loss and indicates that efforts to regenerate nerve fibers may find a ready cochlear substrate for innervation and resumption of function.

A new paradigm of hearing loss and preservation with cochlear implants: Learnings from fundamental studies and clinical research

In 2010 Cochlear initiated a coordinated preclinical research program to identify the factors and underlying mechanisms of acoustic hearing loss following cochlear implantation and device use. At its inception the program was structured around several major hypotheses implicated in the loss of acoustic hearing. The understanding of causes evolved over the course of the program, leading to an increased appreciation of the role of the biological response in post-implant hearing loss. A systematic approach was developed which mapped the cochlear implant journey along a timeline that considers all events in an individual's hearing history. By evaluating the available data in this context, rather than by discrete hypothesis testing, causative and associated factors may be more readily detected. This approach presents opportunities for more effective research management and may aid in identifying new prospects for intervention. Many of the outcomes of the research program apply beyond preservation of acoustic hearing to factors important to overall cochlear health and considerations for future therapies.

Monitoring Cochlear Health With Intracochlear Electrocochleography During Cochlear Implantation: Findings From an International Clinical Investigation

OBJECTIVES

Electrocochleography (ECochG) is emerging as a tool for monitoring cochlear function during cochlear implant (CI) surgery. ECochG may be recorded directly from electrodes on the implant array intraoperatively. For low-frequency stimulation, its amplitude tends to rise or may plateau as the electrode is inserted. The aim of this study was to explore whether compromise of the ECochG signal, defined as a fall in its amplitude of 30% or more during insertion, whether transient or permanent, is associated with poorer postoperative acoustic hearing, and to examine how preoperative hearing levels may influence the ability to record ECochG. The specific hypotheses tested were threefold: (a) deterioration in the pure-tone average of low-frequency hearing at the first postoperative follow-up interval (follow-up visit 1 [FUV1], 4 to 6 weeks) will be associated with compromise of the cochlear microphonic (CM) amplitude during electrode insertion (primary hypothesis); (b) an association is observed at the second postoperative follow-up interval (FUV2, 3 months) (secondary hypothesis 1); and (c) the CM response will be recorded earlier during electrode array insertion when the preoperative high-frequency hearing is better (secondary hypothesis 2).

DESIGN

International, multi-site prospective, observational, between groups design, targeting 41 adult participants in each of two groups, (compromised CM versus preserved CM). Adult CI candidates who were scheduled to receive a Cochlear Nucleus CI with a Slim Straight or a Slim Modiolar electrode array and had a preoperative audiometric low-frequency average thresholds of ≤80 dB HL at 500, 750, and 1000 Hz in the ear to be implanted, were recruited from eight international implant sites. Pure tone audiometry was measured preoperatively and at postoperative visits (FUV1 and follow-up visit 2 [FUV2]). ECochG was measured during and immediately after the implantation of the array.

RESULTS

From a total of 78 enrolled individuals (80 ears), 77 participants (79 ears) underwent surgery. Due to protocol deviations, 18 ears (23%) were excluded. Of the 61 ears with ECochG responses, amplitudes were < 1 µV throughout implantation for 18 ears (23%) and deemed "unclear" for classification. EcochG responses >1 µV in 43 ears (55%) were stable throughout implantation for 8 ears and compromised in 35 ears. For the primary endpoint at FUV1, 7/41 ears (17%) with preserved CM had a median hearing loss of 12.6 dB versus 34/41 ears (83%) with compromised CM and a median hearing loss of 26.9 dB ( p < 0.014). In assessing the practicalities of measuring intraoperative ECochG, the presence of a measurable CM (>1 µV) during implantation was dependent on preoperative, low-frequency thresholds, particularly at the stimulus frequency (0.5 kHz). High-frequency, preoperative thresholds were also associated with a measurable CM > 1 µV during surgery.

CONCLUSIONS

Our data shows that CM drops occurring during electrode insertion were correlated with significantly poorer hearing preservation postoperatively compared to CMs that remained stable throughout the electrode insertion. The practicality of measuring ECochG in a large cohort is discussed, regarding the suggested optimal preoperative low-frequency hearing levels ( < 80 dB HL) considered necessary to obtain a CM signal >1 µV.

Multi-Frequency Electrocochleography and Electrode Scan to Identify Electrode Insertion Trauma during Cochlear Implantation

Intraoperative electrocochleography (ECOG) is performed using a single low-frequency acoustic stimulus (e.g., 500 Hz) to monitor cochlear microphonics (CM) during cochlear implant (CI) electrode insertion. A decrease in CM amplitude is commonly associated with cochlear trauma and is used to guide electrode placement. However, advancement of the recording electrode beyond the sites of CM generation can also lead to a decrease in CM amplitude and is sometimes interpreted as cochlear trauma, resulting in unnecessary electrode manipulation and increased risk of cochlear trauma during CI electrode placement. In the present study, multi-frequency ECOG was used to monitor CM during CI electrode placement. The intraoperative CM tracings were compared with electrode scan measurements, where CM was measured for each of the intracochlear electrodes. Comparison between the peak CM amplitude measured during electrode placement and electrode scan measurements was used to differentiate between different mechanisms for decrease in CM amplitude during CI electrode insertion. Analysis of the data shows that both multi-frequency electrocochleography and electrode scan could potentially be used to differentiate between different mechanisms for decreasing CM amplitude and providing appropriate feedback to the surgeon during CI electrode placement.

Classification of Acoustic Hearing Preservation After Cochlear Implantation Using Electrocochleography

The objective to preserve residual hearing during cochlear implantation has recently led to the use of intracochlear electrocochleography (ECochG) as an intraoperative monitoring tool. Currently, a decrease in the amplitude of the difference between responses to alternating-polarity stimuli (DIF response), predominantly reflecting the hair cell response, is used for providing feedback. Including other ECochG response components, such as phase changes and harmonic distortions, could improve the accuracy of surgical feedback. The objectives of the present study were (1) to compare simultaneously recorded stepwise intracochlear and extracochlear ECochG responses to 500 Hz tone bursts, (2) to explore patterns in features extracted from the intracochlear ECochG recordings relating to hearing preservation or hearing loss, and (3) to design support vector machine (SVM) and random forest (RF) classifiers of acoustic hearing preservation that treat each subject as a sample and use all intracochlear ECochG recordings made during electrode array insertion for classification. Forty subjects undergoing cochlear implant (CI) surgery at the Oslo University Hospital, St. Thomas' Hearing Implant Centre, or the University Hospital of Zurich were prospectively enrolled. In this cohort, DIF response amplitude decreases did not relate to postoperative acoustic hearing preservation. Exploratory analysis of the feature set extracted from the ECochG responses and preoperative audiogram showed that the features were not discriminative between outcome classes. The SVM and RF classifiers that were trained on these features could not distinguish cases with hearing loss and hearing preservation. These findings suggest that hearing loss following CI surgery is not always reflected in intraoperative ECochG recordings.

Electrocochleographic Patterns Predicting Increased Impedances and Hearing Loss after Cochlear Implantation

OBJECTIVES

Different patterns of electrocochleographic responses along the electrode array after insertion of the cochlear implant electrode array have been described. However, the implications of these patterns remain unclear. Therefore, the aim of the study was to correlate different peri- and postoperative electrocochleographic patterns with four-point impedance measurements and preservation of residual hearing.

DESIGN

Thirty-nine subjects with residual low-frequency hearing which were implanted with a slim-straight electrode array could prospectively be included. Intracochlear electrocochleographic recordings and four-point impedance measurements along the 22 electrodes of the array (EL, most apical EL22) were conducted immediately after complete insertion and 3 months after surgery. Hearing preservation was assessed after 3 months.

RESULTS

In perioperative electrocochleographic recordings, 22 subjects (56%) showed the largest amplitude around the tip of the electrode array (apical-peak, AP, EL20 or EL22), whereas 17 subjects (44%) exhibited a maximum amplitude in more basal regions (mid-peak, MP, EL18 or lower). At 3 months, in six subjects with an AP pattern perioperatively, the location of the largest electrocochleographic response had shifted basally (apical-to-mid-peak, AP-MP). Latency was analyzed along the electrode array when this could be discerned. This was the case in 68 peri- and postoperative recordings (87% of all recordings, n = 78). The latency increased with increasing insertion depth in AP recordings (n = 38, median of EL with maximum latency shift = EL21). In MP recordings (n = 30), the maximum latency shift was detectable more basally (median EL12, p < 0.001). Four-point impedance measurements were available at both time points in 90% (n = 35) of all subjects. At the 3-month time point, recordings revealed lower impedances in the AP group (n = 15, mean = 222 Ω, SD = 63) than in the MP (n = 14, mean = 295 Ω, SD= 7 6) and AP-MP groups (n = 6, mean = 234 Ω, SD = 129; AP versus MP p = 0.026, AP versus AP-MP p = 0.023, MP versus AP-MP p > 0.999). The amplitudes of perioperative AP recordings showed a correlation with preoperative hearing thresholds (r2=0.351, p = 0.004). No such correlation was detectable in MP recordings (r2 = 0.033, p = 0.484). Audiograms were available at both time points in 97% (n = 38) of all subjects. The mean postoperative hearing loss in the AP group was 13 dB (n = 16, SD = 9). A significantly larger hearing loss was detectable in the MP and AP-MP groups with 28 (n = 17, SD = 10) and 35 dB (n = 6, SD = 13), respectively (AP versus MP p = 0.002, AP versus AP-MP p = 0.002, MP versus AP-MP p = 0.926).

CONCLUSION

MP and AP-MP response patterns of the electrocochleographic responses along the electrode array after cochlear implantation are correlated with higher four-point impedances and poorer postoperative hearing compared to AP response patterns. The higher impedances suggest that MP and AP-MP patterns are associated with increased intracochlear fibrosis.

Clinical perspective on hearing preservation in cochlear implantation, the University of Iowa experience

Preservation of residual acoustic hearing has emerged as an important concept for those individuals undergoing cochlear implantation with residual low frequency hearing. Acoustic plus electric speech processing improves hearing outcomes in quiet, enables melody recognition, preserves spatial hearing if there is acoustic hearing in both ears and significantly improves hearing in noise. The development of our experience with acoustic plus electric processing is reviewed along with clinical trials and patient outcomes that our team has documented over the past twenty years.

Relationship Between Intraoperative Electrocochleography Responses and Immediate Postoperative Bone Conduction Thresholds in Cochlear Implantation

OBJECTIVE

To determine the relationship between intraoperative electrocochleography (ECochG) measurements and residual hearing preservation after cochlear implant (CI) surgery by comparing differences between preoperative and immediate postoperative bone conduction thresholds.

STUDY DESIGN

Prospective cohort study.

SETTING

Tertiary academic referral center.

PATIENTS

Sixteen patients with preoperative residual hearing and measurable (no-vibrotactile) bone conduction thresholds at 250 and/or 500 Hz who underwent cochlear implantation.

MAIN OUTCOME MEASURE

Intraoperative ECochG and air and bone conduction thresholds.

RESULTS

Nine patients showed no significant drop (<30%) in ECochG amplitude during CI surgery with an average preoperative and immediate postoperative BC threshold of 46 and 39 dB HL, respectively, at 500 Hz. Seven patients with a decrease in ECochG amplitude of 30% or greater showed an average preoperative 500 Hz BC threshold of 32 dB HL and immediate postoperative threshold of 55 dB HL. Air and bone conduction thresholds measured approximately 1 month after CI surgery show delayed-onset of hearing loss across our study patients.

CONCLUSIONS

A small decrease (<30%) in difference response or cochlear microphonics amplitude correlates with no significant changes in immediate postoperative residual hearing, whereas patients who show larger changes (≥30%) in difference response or cochlear microphonics amplitude during intraoperative ECochG measurements show significant deterioration in BC thresholds. This study reveals the necessity of prompt postoperative bone conduction measurement to isolate the intraoperative cochlear trauma that may be detected during intraoperative ECochG measurements. Although delayed postoperative audiometrics represent longer-term functional hearing, it includes the sum of all postoperative changes during the recovery period, including subacute changes after implantation that may occur days or weeks later. Measuring air and bone conduction thresholds immediately postoperatively will better isolate factors influencing intraoperative, early postoperative, and delayed postoperative hearing loss. This will ultimately help refine surgical technique, device design, and highlight the use of intraoperative ECochG in monitoring cochlear trauma during CI surgery.

Can Electrocochleography Help Preserve Hearing After Cochlear Implantation With Full Electrode Insertion?

OBJECTIVES

To evaluate the utility of intracochlear electrocochleography (ECochG) monitoring during cochlear implant (CI) surgery on postoperative hearing preservation.

STUDY DESIGN

Prospective, randomized clinical trial.

SETTING

Ten high-volume, tertiary care CI centers.

PATIENTS

Adult patients with sensorineural hearing loss meeting the CI criteria who selected an Advanced Bionics CI.

METHODS

Patients were randomized to CI surgery either with audible ECochG monitoring available to the surgeon during electrode insertion or without ECochG monitoring. Hearing preservation was determined by comparing preoperative unaided low-frequency (125-, 250-, and 500-Hz) pure-tone average (LF-PTA) to postoperative LF-PTA at CI activation. Pre- and post-CI computed tomography was used to determine electrode scalar location and electrode translocation.

RESULTS

Eighty-five adult CI candidates were enrolled. The mean (standard deviation [SD]) unaided preoperative LF-PTA across the sample was 54 (17) dB HL. For the whole sample, hearing preservation was "good" (i.e., LF-PTA change 0-15 dB) in 34.5%, "fair" (i.e., LF-PTA change >15-29 dB) in 22.5%, and "poor" (i.e., LF-PTA change ≥30 dB) in 43%. For patients randomized to ECochG "on," mean (SD) LF-PTA change was 27 (20) dB compared with 27 (23) dB for patients randomized to ECochG "off" ( p = 0.89). Seven percent of patients, all of whom were randomized to ECochG off, showed electrode translocation from the scala tympani into the scala vestibuli.

CONCLUSIONS

Although intracochlear ECochG during CI surgery has important prognostic utility, our data did not show significantly better hearing preservation in patients randomized to ECochG "on" compared with ECochG "off."

Automatic analysis of cochlear response using electrocochleography signals during cochlear implant surgery

Cochlear implants (CIs) provide an opportunity for the hearing impaired to perceive sound through electrical stimulation of the hearing (cochlear) nerve. However, there is a high risk of losing a patient’s natural hearing during CI surgery, which has been shown to reduce speech perception in noisy environments as well as music appreciation. This is a major barrier to the adoption of CIs by the hearing impaired. Electrocochleography (ECochG) has been used to detect intra-operative trauma that may lead to loss of natural hearing. There is early evidence that ECochG can enable early intervention to save natural hearing of the patient. However, detection of trauma by observing changes in the ECochG response is typically carried out by a human expert. Here, we discuss a method of automating the analysis of cochlear responses during CI surgery. We establish, using historical patient data, that the proposed method is highly accurate (∼94% and ∼95% for sensitivity and specificity respectively) when compared to a human expert. The automation of real-time cochlear response analysis is expected to improve the scalability of ECochG and improve patient safety.

The Relation of Cochlear Implant Electrode Array Type and Position on Continued Hearing Preservation

OBJECTIVE

To analyze the relationship of electrode array (EA) type and position on hearing preservation longevity following cochlear implantation.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary referral center.

PATIENTS

Adult cochlear implant recipients between 2013 and 2019 with hearing preserved postoperatively and postoperative CT scans.

INTERVENTIONS

CT scan analysis of EA position. Stepwise regression to determine influence of EA position, EA type, and patient demographics on postoperative low frequency hearing.

MAIN OUTCOME MEASURES

Low frequency pure tone average (LFPTA), LFPTA shift, angular insertion depth, base insertion depth, scalar position, mean perimodiolar distance.

RESULTS

Of 792 cochlear implant recipients, 121 had preoperative LFPTA <80 dB HL with 60 of the 121 (49.6%) implanted with straight, 32 (26.4%) with precurved, styletted, and 29 (24.0%) implanted precurved, nonstyletted EA. Mean follow up was 28.6 months (range 1-103). There was no statistically significant difference in activation, 6- and 12-month, and last follow-up LFPTA (125, 250, and 500 Hz) shift based on EA type (straight p = 0.302, precurved, styletted p = 0.52, precurved, nonstyletted p = 0.77). Preoperative LFPTA and age of implantation were significant predictors of LFPTA shift at activation, accounting for 30.8% of variance ( F [2, 113] = 26.603, p < 0.0001). LFPTA shift at activation, scalar position, and base insertion depth were significant predictors of variability and accounted for 39.1% of variance in LFPTA shift at 6 months ( F [3, 87] = 20.269, p < 0.0001). Only LFPTA shift at 12 months was found to be a significant predictor of LFPTA shift at last follow up, accounting for 41.0% of variance ( F [1, 48] = 32.653, p < 0.0001).

CONCLUSIONS

Patients had excellent long-term residual hearing regardless of EA type. Age, preoperative acoustic hearing, and base insertion depth may predict short term preservation, while 12-month outcomes significantly predicted long-term hearing preservation.

Natural course of residual hearing preservation with a slim, modiolar cochlear implant electrode array

PURPOSE

Understanding residual hearing preservation and its natural course following cochlear implantation is important for developing rehabilitation strategies for hearing loss. However, non-uniform evaluation criteria and varying surgical skills pose challenges in fair comparison of the effect of different electrodes on residual hearing preservation. We compared the effect of a slim modiolar electrode (SME) and a slim straight electrode (SSE), implanted by a single surgeon, on progression of residual hearing using different parameters, based on cross-sectional and longitudinal audiological analyses.

METHODS

Patients with preoperative low-frequency pure-tone average (LFPTA) ≤85 dB at 250 and 500 Hz and who underwent minimally traumatic surgical techniques were included. The progression of residual hearing using threshold shifts, hearing preservation rate according to the HEARRING classification, and maintenance of functional low-frequency hearing potentially qualifying for a hybrid stimulation was analyzed up to five time points throughout the 1-year follow-up period.

RESULTS

Threshold shifts and hearing preservation rates according to the HEARRING classification of the electrodes were comparable from 3 months through 12 months postoperatively. Maintenance of functional low-frequency hearing, required for the usage of a hybrid stimulation, was similar for both electrodes. A substantial proportion of implantees with SME use a hybrid stimulation, resulting in long-term use. However, a difference in the pattern of postoperative residual hearing preservation between the two electrodes is possible, probably due to differences in their physical characteristics and location. Specifically, correlation analysis exhibited that significantly less tight modiolar proximity negatively affect the residual hearing preservation, albeit only at 3 months postoperatively, among patients with the SME.

CONCLUSION

Collectively, both SME and SSE implantation showed favorable residual hearing preservation. Our findings further refine the recently proposed hearing preservation with the SME and suggest that the physical characteristics and location of electrodes, in terms of electrode-to-modiolus distance, could affect loss of acoustic hearing in various ways.

Is Characteristic Frequency Limiting Real-Time Electrocochleography During Cochlear Implantation?

Objectives

Electrocochleography (ECochG) recordings during cochlear implantation have shown promise in estimating the impact on residual hearing. The purpose of the study was (1) to determine whether a 250-Hz stimulus is superior to 500-Hz in detecting residual hearing decrement and if so; (2) to evaluate whether crossing the 500-Hz tonotopic, characteristic frequency (CF) place partly explains the problems experienced using 500-Hz.

Design

Multifrequency ECochG comprising an alternating, interleaved acoustic complex of 250- and 500-Hz stimuli was used to elicit cochlear microphonics (CMs) during insertion. The largest ECochG drops (≥30% reduction in CM) were identified. After insertion, ECochG responses were measured using the individual electrodes along the array for both 250- and 500-Hz stimuli. Univariate regression was used to predict whether 250- or 500-Hz CM drops explained low-frequency pure tone average (LFPTA; 125-, 250-, and 500-Hz) shift at 1-month post-activation. Postoperative CT scans were performed to evaluate cochlear size and angular insertion depth.

Results

For perimodiolar insertions (N = 34), there was a stronger linear correlation between the largest ECochG drop using 250-Hz stimulus and LFPTA shift (r = 0.58), compared to 500-Hz (r = 0.31). The 250- and 500-Hz CM insertion tracings showed an amplitude peak at two different locations, with the 500-Hz peak occurring earlier in most cases than the 250-Hz peak, consistent with tonotopicity. When using the entire array for recordings after insertion, a maximum 500-Hz response was observed 2-6 electrodes basal to the most-apical electrode in 20 cases (58.9%). For insertions where the apical insertion angle is >350 degrees and the cochlear diameter is <9.5 mm, the maximum 500-Hz ECochG response may occur at the non-apical most electrode. For lateral wall insertions (N = 14), the maximum 250- and 500-Hz CM response occurred at the most-apical electrode in all but one case.

Conclusion

Using 250-Hz stimulus for ECochG feedback during implantation is more predictive of hearing preservation than 500-Hz. This is due to the electrode passing the 500-Hz CF during insertion which may be misidentified as intracochlear trauma; this is particularly important in subjects with smaller cochlear diameters and deeper insertions. Multifrequency ECochG can be used to differentiate between trauma and advancement of the apical electrode beyond the CF.

Relationship Between Intraoperative Electrocochleography and Hearing Preservation

OBJECTIVES

To compare intraoperative intracochlear electrocochleography (ECochG) with hearing preservation outcomes in cochlear implant (CI) subjects.

DESIGN

Intraoperative electrocochleography was performed in adult CI subjects who were recipients of Advanced Bionics' Bionics LLC precurved HiFocus MidScala or straight HiFocus SlimJ electrode arrays. ECochG responses were recorded from the most apical electrode contact during insertion. No changes to the insertions were made due to ECochG monitoring. No information about insertion resistance was collected. ECochG drops were estimated as the change in amplitude from peak (defined as maximum amplitude response) to drop (largest drop) point after the peak during insertion was measured following the peak response. Audiometric thresholds from each subject were obtained before and approximately 1 month after CI surgery. The change in pure tone average for frequencies between 125 Hz and 500 Hz was measured after surgery. No postoperative CT scans were collected as part of this study.

RESULTS

A total of 68 subjects from five surgical centers participated in the study. The study sample included 30 MidScala and 38 SlimJ electrodes implanted by approximately 20 surgeons who contributed to the study. Although a wide range of results were observed, there was a moderate positive correlation (Pearson Correlation coefficient, r = 0.56, p < 0.01) between the size of the ECochG drop and the magnitude of pure tone average change. This trend was present for both the MidScala and SlimJ arrays. The SlimJ and MidScala arrays produced significantly different hearing loss after surgery.

CONCLUSION

Large ECochG amplitude drops observed during electrode insertion indicated poorer hearing preservation. Although the outcomes were variable, this information may be helpful to guide surgical decision-making when contemplating full electrode insertion and the likelihood of hearing preservation.

Implications of Phase Changes in Extracochlear Electrocochleographic Recordings During Cochlear Implantation

OBJECTIVE

To assess the prevalence and implications of phase changes in extracochlear electrocochleography (ECochG) recordings during cochlear implantation.

MATERIALS AND METHODS

Extracochlear ECochG recordings were performed before and after insertion of the cochlear implant (CI) electrode by a recording electrode placed on the promontory. Acoustic stimuli were tone bursts at 250, 500, 750, and 1,000 Hz. The pure tone average (PTA) was determined before and approximately 4 weeks after surgery.

RESULTS

Extracochlear ECochG recordings in 69 ears of 68 subjects were included. At 250 Hz, the mean phase change was 43° (n = 50, standard deviation (SD) 44°), at 500 Hz 36° (n = 64, SD 36°), at 750 Hz 33° (n = 42, SD 39°), and at 1,000 Hz 22° (n = 54, SD 27°). Overall, in 48 out of 210 ECochG recordings a phase change of ≥45° (23%) was detectable. Ears with an amplitude drop >3 dB and a phase change ≥45° (n = 3) had a complete or near complete loss of residual cochlear function in all cases. A phase change of ≥90° in one recording was not associated with a larger amplitude change of the ECochG signal (1.9 dB vs. -0.9 dB, p = 0.1052, n = 69), but with a significantly larger postoperative hearing loss (17 dB vs. 26 dB, p = 0.0156, n = 69).

CONCLUSIONS

Phase changes occur regularly in extracochlear ECochG recordings during cochlear implantation. Phase changes of ≥90° with or without amplitude changes in the ECochG signal are associated with a larger postoperative hearing loss and could therefore represent an independent marker for cochlear trauma or changes of inner ear mechanics relevant for the postoperative hearing outcome.

Digital Live Imaging of Intraoperative Electrocochleography - First Description of Feasibility and Hearing Preservation During Cochlear Implantation

INTRODUCTION

Intraoperative electrocochleography (ECochG) during cochlear implantation is a promising tool to preserve residual hearing. However, the time gap between insertion of the electrode and acoustic feedback from the audiologist to the surgeon can cause delay and subsequently irreparable damage to cochlear structures. In this feasibility study, for the first time, real-time visualization of intraoperative ECochG via digital microscope display directly to the surgeon was successfully performed in four patients.

MATERIALS AND METHODS

Four patients with residual hearing underwent cochlear implantation. Intraoperative electrocochleography responses were collected and direct visualization during the time of electrode insertion into the surgeon's field of view in the binoculars using augmented real-time digital imaging was realized. The time of electrode insertion was recorded. Hearing preservation was determined by testing postoperative changes in behavioral thresholds.

RESULTS

Digital live visualization of intraoperative ECochG using image augmentation in a digital microscope was successfully performed in all cases and enabled direct adaptation of the surgeon's insertion behavior. Mean time of electrode insertion was 129.8 seconds. Postoperative behavioral thresholds were comparable to preoperative taken thresholds. Preservation of residual hearing in the low frequency range was possible.

DISCUSSION

This study is the first to describe digital visualization of intraoperative electrocochleography as a new method enabling the surgeon to directly react to changes in amplitude of the cochlea microphonics. Our results show that augmentation of the intraoperative live imaging with electrical potentials could add to hearing preservation during cochlear implantation.

Real Time Monitoring During Cochlear Implantation: Increasing the Accuracy of Predicting Residual Hearing Outcomes

OBJECTIVES

Real-time electrocochleography (rt-ECochG) is a method to detect intracochlear potential changes during cochlear implantation (CI). Steep amplitude drops of the cochlear microphonic (CM) signal (so called "ECochG events") have been correlated with worse residual hearing outcomes. However, the sensitivity and specificity of monitoring CM amplitude on its own are too low to use it as a biomarker. The aim of this article was to establish if additional signal components would help to better predict postoperative hearing outcomes.

DESIGN AND SETTING

Single-center, prospective cohort study at a tertiary referral hospital.

PARTICIPANTS AND INTERVENTIONS

Between 2017 and 2020, we included 73 adult patients receiving a lateral wall cochlear implant electrode. During electrode insertion, rt-ECochG measurements were performed.

MAIN OUTCOMES

We calculated a multiple regression analysis for patients with one ECochG event. The dependant variable was the relative acoustic hearing result 4 weeks after surgery. Independent variables were CM latency, a ratio of the auditory nerve neurophonic to the CM (the ANN/CM index) as well as CM signal recovery.

RESULTS

The change of the ANN/CM index linearly correlated with acoustic hearing outcomes 4 weeks after surgery. Adding this factor led to a statistically significant increase in the variance accounted for by the regression model.

CONCLUSIONS

When monitoring the implantation process with rt-ECochG, prediction of postoperative hearing thresholds is improved by addition of the ANN/CM index to a model that includes CM amplitude fluctuation.

Evaluation of hearing preservation in adults with a slim perimodiolar electrode

PURPOSE

Numerous endeavors have been undertaken to preserve hearing in cochlear implant (CI) patients. Particularly, optimization of electrode array design aims at preservation of residual hearing (RH). This study examines whether a slim perimodiolar (PM) electrode array could bear the capability to preserve hearing.

METHODS

A total of 47 patients underwent cochlear implantation receiving the PM electrode. (i) Patients with pure tone audiogram (PTA) thresholds better than 85 dB and/or hearing loss for Freiburg speech test numbers less than 60 dB and more than 50% maximum monosyllabic understanding were assigned to the RH group (n = 17), while all others belonged to the noRH group (n = 30). (ii) Another group implanted with a slim straight, lateral wall (LW) electrode was recruited for comparison.

RESULTS

We compared 17 RH-30 noRH patients all receiving the PM electrode. RH in PM recipients decreased faster than in LW recipients. No significant differences were observed between both (RH v/s noRH) groups in NRT thresholds, Freiburg speech test and A§E^® phonemes. Analogous satisfaction levels were indicated through the questionnaires in terms of sound quality, hearing in silence, noise and directional hearing in both groups.

CONCLUSIONS

The results suggest that hearing preservation is influenced not only by electrode shape but various factors. This study opens an avenue for further investigations to elucidate and enumerate the causes for progressive hearing loss.

Electrocochleography in Cochlear Implant Users with Residual Acoustic Hearing: A Systematic Review

(1) Objectives: This study reviews the use of electrocochleography (ECoG) as a tool for assessing the response of the peripheral auditory system and monitoring hearing preservation in the growing population of cochlear implant (CI) users with preserved hearing in the implanted ear. (2) Methods: A search was conducted in PubMed and CINAHL databases up to August 2020 to locate articles related to the ECoG measured during or after the cochlear implant (CI) surgery for monitoring purposes. Non-English articles, animal studies, literature reviews and editorials, case reports, and conference papers were excluded. The quality of studies was evaluated using the National Institute of Health (NIH) "Study Quality Assessment Tool for Case Series Studies". (3) Results: A total 30 articles were included for the systematic review. A total of 21 articles were intraoperative ECoG studies, while seven articles were postoperative studies. Two studies were conducted ECoG both during and after the surgery. Intraoperative ECoG studies focused on monitoring changes in ECoG response amplitudes during and/or after electrode insertion and predicting the scalar location of the electrode array. Postoperative ECoG studies focused on using the ECoG measurements to estimate behavioral audiometric thresholds and monitor pathophysiological changes related to delayed onset hearing loss postimplant. (4) Conclusions: ECoG is feasible to provide real-time feedback intraoperatively and has a potential clinical value to monitor the status of hearing preservation postoperatively in this CI population with residual acoustic hearing.