Early Hearing Preservation Outcomes Following Cochlear Implantation With New Slim Lateral Wall Electrode Using Electrocochleography

Electrocochleography-Based Tonotopic Map: I. Place Coding of the Human Cochlea With Hearing Loss

OBJECTIVES

Due to the challenges of direct in vivo measurements in humans, previous studies of cochlear tonotopy primarily utilized human cadavers and animal models. This study uses cochlear implant electrodes as a tool for intracochlear recordings of acoustically evoked responses to achieve two primary goals: (1) to map the in vivo tonotopy of the human cochlea, and (2) to assess the impact of sound intensity and the creation of an artificial "third window" on this tonotopic map.

DESIGN

Fifty patients with hearing loss received cochlear implant electrode arrays. Postimplantation, pure-tone acoustic stimuli (0.25 to 4 kHz) were delivered, and electrophysiological responses were recorded from all 22 electrode contacts. The analysis included fast Fourier transformation to determine the amplitude of the first harmonic, indicative of predominantly outer hair cell activity, and tuning curves to identify the best frequency (BF) electrode. These measures, coupled with postoperative imaging for precise electrode localization, facilitated the construction of an in vivo frequency-position function. The study included a specific examination of 2 patients with auditory neuropathy spectrum disorder (ANSD), with preserved cochlear function as assessed by present distortion-product otoacoustic emissions, to determine the impact of sound intensity on the frequency-position map. In addition, the electrophysiological map was recorded in a patient undergoing a translabyrinthine craniotomy for vestibular schwannoma removal, before and after creating an artificial third window, to explore whether an experimental artifact conducted in cadaveric experiments, as was performed in von Békésy landmark experiments, would produce a shift in the frequency-position map.

RESULTS

A significant deviation from the Greenwood model was observed in the electrophysiological frequency-position function, particularly at high-intensity stimulations. In subjects with hearing loss, frequency tuning, and BF location remained consistent across sound intensities. In contrast, ANSD patients exhibited Greenwood-like place coding at low intensities (~40 dB SPL) and a basal shift in BF location at higher intensities (~70 dB SPL or greater). Notably, creating an artificial "third-window" did not alter the frequency-position map.

CONCLUSIONS

This study successfully maps in vivo tonotopy of human cochleae with hearing loss, demonstrating a near-octave shift from traditional frequency-position maps. In patients with ANSD, representing more typical cochlear function, intermediate intensity levels (~70 to 80 dB SPL) produced results similar to high-intensity stimulation. These findings highlight the influence of stimulus intensity on the cochlear operational point in subjects with hearing loss. This knowledge could enhance cochlear implant programming and improve auditory rehabilitation by more accurately aligning electrode stimulation with natural cochlear responses.

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.

Improved Cochlear Implant Performance Estimation Using Tonotopic-Based Electrocochleography

Importance

Cochlear implantation produces remarkable results in postlingual deafness, although auditory outcomes vary. Electrocochleography (ECochG) has emerged as a valuable tool for assessing the cochlear-neural substrate and evaluating patient prognosis.

Objective

To assess whether ECochG-total response (ECochG-TR) recorded at the best-frequency electrode (BF-ECochG-TR) correlates more strongly with speech perception performance than ECochG-TR measured at the round window (RW-ECochG-TR).

Design, Setting, and Participants

This single-center cross-sectional study recruited 142 patients from July 1, 2021, to April 30, 2022, with 1-year follow-up. Exclusions included perilymph suctioning, crimped sound delivery tubes, non-native English speakers, inner ear malformations, nonpatent external auditory canals, or cochlear implantation revision surgery.

Exposures

Cochlear implantation.

Main Outcomes and Measures

Speech perception testing, including the consonant-nucleus-consonant (CNC) words test, AzBio sentences in quiet, and AzBio sentences in noise plus 10-dB signal to noise ratio (with low scores indicating poor performance and high scores indicating excellent performance on all tests), at 6 months postoperatively; and RW-ECochG-TR and BF-ECochG-TR (measured for 250, 500, 1000, and 2000 Hz).

Results

A total of 109 of the 142 eligible postlingual adults (mean [SD] age, 68.7 [15.8] years; 67 [61.5%] male) were included in the study. Both BF-ECochG-TR and RW-ECochG-TR were correlated with 6-month CNC scores (BF-ECochG-TR: r = 0.74; 95% CI, 0.62-0.82; RW-ECochG-TR: r = 0.67; 95% CI, 0.54-0.76). A multivariate model incorporating age, duration of hearing loss, and angular insertion depth did not outperform BF-ECochG-TR or RW-ECochG-TR alone. The BF-ECochG-TR correlation with CNC scores was significantly stronger than the RW-ECochG-TR correlation (r difference = -0.18; 95% CI, -0.31 to -0.01; z = -2.02). More moderate correlations existed between 6-month AzBio scores in noise, Montreal Cognitive Assessment (MoCA) scores (r = 0.46; 95% CI, 0.29-0.60), and BF-ECochG-TR (r = 0.42; 95% CI, 0.22-0.58). MoCA and the interaction between BF-ECochG-TR and MoCA accounted for a substantial proportion of variability in AzBio scores in noise at 6 months (R2 = 0.50; 95% CI, 0.36-0.61).

Conclusions and Relevance

In this case series, BF-ECochG-TR was identified as having a stronger correlation with cochlear implantation performance than RW-ECochG-TR, although both measures highlight the critical role of the cochlear-neural substrate on outcomes. Demographic, audiologic, and surgical factors demonstrated weak correlations with cochlear implantation performance, and performance in noise was found to require a robust cochlear-neural substrate (BF-ECochG-TR) as well as sufficient cognitive capacity (MoCA). Future cochlear implantation studies should consider these variables when assessing performance and related interventions.

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.