The effects of cochlear implant electrode deactivation on speech perception and in predicting device failure. Otol Neurotol. 2009;30:7-13. [PMID: 18833018 DOI: 10.1097/mao.0b013e31818a08ba]

Auditory nerve fiber excitability for alternative electrode placement in the obstructed human cochlea: electrode insertion in scala vestibuli versus scala tympani

Objective. The cochlear implant (CI) belongs to the most successful neuro-prostheses. Traditionally, the stimulating electrode arrays are inserted into the scala tympani (ST), the lower cochlear cavity, which enables simple surgical access. However, often deep insertion is blocked, e.g. by ossification, and the auditory nerve fibers (ANFs) of lower frequency regions cannot be stimulated causing severe restrictions in speech understanding. As an alternative, the CI can be inserted into the scala vestibuli (SV), the other upper cochlear cavity.Approach. In this computational study, the excitability of 25 ANFs are compared for stimulation with ST and SV implants. We employed a 3-dimensional realistic human cochlear model with lateral wall electrodes based on aμ-CT dataset and manually traced fibers. A finite element approach in combination with a compartment model of a spiral ganglion cell was used to simulate monophasic stimulation with anodic (ANO) and cathodic (CAT) pulses of 50μs.Main results. ANO thresholds are lower in ST (mean/std =μ/σ= 189/55μA) stimulation compared to SV (μ/σ= 323/119μA) stimulation. Contrary, CAT thresholds are higher for the ST array (μ/σ= 165/42μA) compared to the SV array (μ/σ= 122/46μA). The threshold amplitude depends on the specific fiber-electrode spatial relationship, such as lateral distance from the cochlear axis, the angle between electrode and target ANF, and the curvature of the peripheral process. For CAT stimulation the SV electrodes show a higher selectivity leading to less cross-stimulation of additional fibers from different cochlear areas.Significance. We present a first simulation study with a human cochlear model that investigates an additional CI placement into the SV and its impact on the excitation behavior. Results predict comparable outcomes to ST electrodes which confirms that SV implantation might be an alternative for patients with a highly obstructed ST.

Variation of electrical impedance over 5 years post-implantation and relationship with the maximum comfort level (MCL) in adults with cochlear implants

INTRODUCTION

The maximum comfort level (MCL), threshold level (THR) and electrical impedance change in the postoperative period of the cochlear implant for months until they stabilize. The objective of this article is to establish the variation during 5 post-surgical years of impedance, and its relationship with MCL in unilaterally implanted adults.

METHODS

Retrospective study over 5 years, with 78 adult patients implanted with MED-EL in a tertiary hospital from the year 2000 to 2015. The variation in impedance, MCL and the relationship between them were analyzed in basal (9-12), medial (5-8) and apical electrodes (1-4), performing an inferential ANOVA analysis of repeated measures with comparisons between consecutive times, corrected with Bonferroni criteria.

RESULTS

33 men (42.3%) and 45 women (57.7%), with a mean age of 52.7±14.6 years. "Stability" was considered the time of follow-up without statistically significant differences between one visit and the next. Changes in impedance in medial electrodes ceased to be statistically significant at 3 months, and in apicals at 6 months, with mean values of 5.84 and 6.43kΩ. MCL stabilized at 2 years in basal and apical electrodes, and at 3 years in medial, with mean values of 24.9, 22.7, and 25.6qu. There was a correlation between MCL and impedance in medium electrodes up to 3 months and in apical ones up to one year.

CONCLUSIONS

Electrical impedance drops significantly in medial and apical electrodes up to 3 and 6 months. MCL increases significantly up to two years. Impedance is related to MCL up to 6 months.

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.

Polarity Sensitivity of Human Auditory Nerve Fibers Based on Pulse Shape, Cochlear Implant Stimulation Strategy and Array

Neural health is of great interest to determine individual degeneration patterns for improving speech perception in cochlear implant (CI) users. Therefore, in recent years, several studies tried to identify and quantify neural survival in CI users. Among all proposed techniques, polarity sensitivity is a promising way to evaluate the neural status of auditory nerve fibers (ANFs) in CI users. Nevertheless, investigating neural health based on polarity sensitivity is a challenging and complicated task that involves various parameters, and the outcomes of many studies show contradictory results of polarity sensitivity behavior. Our computational study benefits from an accurate three-dimensional finite element model of a human cochlea with realistic human ANFs and determined ANF degeneration pattern of peripheral part with a diminishing of axon diameter and myelination thickness based on degeneration levels. In order to see how different parameters may impact the polarity sensitivity behavior of ANFs, we investigated polarity behavior under the application of symmetric and asymmetric pulse shapes, monopolar and multipolar CI stimulation strategies, and a perimodiolar and lateral CI array system. Our main findings are as follows: (1) action potential (AP) initiation sites occurred mainly in the peripheral site in the lateral system regardless of stimulation strategies, pulse polarities, pulse shapes, cochlear turns, and ANF degeneration levels. However, in the perimodiolar system, AP initiation sites varied between peripheral and central processes, depending on stimulation strategies, pulse shapes, and pulse polarities. (2) In perimodiolar array, clusters formed in threshold values based on cochlear turns and degeneration levels for multipolar strategies only when asymmetric pulses were applied. (3) In the perimodiolar array, a declining trend in polarity (anodic threshold/cathodic threshold) with multipolar strategies was observed between intact or slight degenerated cases and more severe degenerated cases, whereas in the lateral array, cathodic sensitivity was noticed for intact and less degenerated cases and anodic sensitivity for cases with high degrees of degeneration. Our results suggest that a combination of asymmetric pulse shapes, focusing more on multipolar stimulation strategies, as well as considering the distances to the modiolus wall, allows us to distinguish the degeneration patterns of ANFs across the cochlea.

Cochlear Implantation in NF2 Patients Without Intracochlear Schwannoma Removal

OBJECTIVE

To determine if cochlear implantation without removal of inner ear schwannomas (IES) is an effective treatment option for Neurofibromatosis 2 (NF2) patients. To determine how the presence of an intracochlear schwannoma might impact cochlear implant (CI) outcomes and programming parameters.

STUDY DESIGN

Retrospective chart review.

SETTING

Tertiary center for cochlear and auditory brainstem implantation.

PATIENTS

Of 10 NF2 patients with IES, 8 are reported with no previous tumor removal on the implanted ear.

INTERVENTIONS

Cochlear implant without tumor removal.

MAIN OUTCOME MEASURES

Performance outcomes with CI at least 1-year post intervention. Programming parameters, including impedances, for patients with IES.

RESULTS

All patients had full insertion of the electrode arrays with round window approaches. Performance outcomes ranged from 0 to 100% for Bamford-Kowal-Bench sentences. Impedance measurements for active electrodes for patients with IES were comparable to those measured in patients without vestibular schwannoma (VS). Only patients who had radiation treatment before receiving their implant had elevated threshold requirements for CI programming compared with CI recipients without VS.

CONCLUSION

Cochlear implantation without tumor removal is an effective option for treating NF2 patients with IES. The presence of an intracochlear tumor did not have an impact on CI performance or programming requirements compared with patients without VS; however, previous treatment with radiation may be related to elevated current requirements in the CI settings.

Predictors of Postoperative Electrode Deactivation Among Adult Cochlear Implantees

OBJECTIVE

To characterize postoperative electrode functionality after adult cochlear implantation; to identify rationale and risk factors for electrode deactivation.

STUDY DESIGN

Retrospective Chart Review.

SETTING

Academic Cochlear Implant Center.

SUBJECT POPULATION

Five hundred nineteen cochlear implants in 433 adult patients over 5 years.

INTERVENTIONS

Unilateral or bilateral cochlear implantation.

MAIN OUTCOME MEASURES

Rate of electrode deactivation after adult cochlear implantation.

RESULTS

One hundred twenty (27.7%) patients experienced electrode deactivation postoperatively, involving a total of 447 electrodes. The most common reasons for deactivation were bothersome nonauditory symptoms (n = 170, 38.0%), perceived benefit by patients (n = 64, 14.3%), and bothersome auditory symptoms (n = 60, 13.4%). Four hundred nineteen (93.7%) of involved electrodes remained deactivated at most recent follow-up, whereas 28 (6.3%) were able to be reactivated. Deactivation was most likely to occur within the first 4 weeks after activation (n = 90 patients,75.0%; p < 0.01). Among affected patients, the average number of electrodes deactivated was 3.44 (range 1-13; SD 2.50). Age was not associated with electrode deactivation.

CONCLUSIONS

While 98% of cochlear implants had full insertions, more than a quarter of implantees may experience electrode deactivation postoperatively for a multitude of reasons, with bothersome nonauditory symptoms most prevalent. Deactivation of five or more electrodes and simultaneous deactivation of two or three electrodes seems to increase the odds of subsequent device failure. However, deactivation encompasses a wide range of issues that likely include patient factors, surgical technique, and device-specific issues. Prognosis varies greatly at the individual level and further evaluation is required to better identify the issues underlying deactivation and identify true predictors of failure.

Incidence, Time Course, and Implications of Electrode Abnormalities in Pediatric Cochlear Implant Recipients

OBJECTIVES

To identify the incidence of specific abnormal impedance patterns or electrode faults, and determine their implication and significance, in a pediatric population of cochlear implant recipients.

DESIGN

Nine hundred fifty-six cochlear implant devices (621 recipients) were included in this retrospective study. Devices were included if the implantation surgery was performed at our tertiary care hospital, and the recipient was 21 years of age or younger at the time the device was implanted. Device models incapable of producing impedance measures by telemetry were excluded from the study. Individual devices with abnormal impedance measures indicating an open circuit (OC), short circuit (SC), or partial short circuit (partial SC) were included in the study, unless these abnormalities occurred only in the OR and not postoperatively. Device and patient characteristics were examined to determine their relationship to increased incidence of electrode faults or atypical patterns.

RESULTS

The incidence of software-identified electrode faults in our exclusively pediatric population was similar to that reported in the literature containing mixed-age cohorts. Nine percent of devices experienced at least one OC or one pair of SCs. Although higher incidence of these faults was seen in some specific device models, the long-term average of these faults was equivalent across manufacturers. No factors examined in this study increased the likelihood of experiencing a software-identified electrode fault. Within the study period under examination (October 1997 to March 2018), partial SCs (presenting as zig-zag or low-flat impedance patterns) were only observed in Cochlear devices. While the incidence of these partial SC abnormalities (non-software-identified faults) was 6% across all models of Cochlear devices, the CI24RCS experienced the highest incidence of partial SCs. The incidence of this pattern was lower in models manufactured after CI24RCS.

CONCLUSIONS

This study provides incidence of various cochlear implant electrode impedance abnormalities across a large cohort of pediatric recipients. The incidence of all electrode abnormalities was relatively low, particularly partial SCs, which are less well recognized and not currently identified by clinician-accessible software. Incidence of software-identified electrode faults (i.e., SCs and OCs) in our pediatric-only study is similar to the incidence reported in other mixed-population and adult-only studies. These common electrode faults generally are not associated with device failure, and clinicians should feel comfortable reassuring families that an individual electrode fault does not imply an impending device failure. Conversely, those atypical impedance patterns not currently flagged by the programming software as abnormal, but visible to the clinician's eye (i.e., partial SCs in zig-zag or low-flat patterns), have a higher likelihood of device damage and failure. Performance in patients with electrode arrays exhibiting these atypical patterns should be closely monitored for any functional decrement, and proactively managed to maintain performance whenever possible.

Deactivating cochlear implant electrodes to improve speech perception: A computational approach

A potential bottleneck to improving speech perception performance in cochlear implant (CI) users is that some of their electrodes may poorly encode speech information. Several studies have examined the effect of deactivating poorly encoding electrodes on speech perception with mixed results. Many of these studies focused on identifying poorly encoding electrodes by some measure (e.g. electrode discrimination, pitch ordering, threshold, CT-guided, masked modulation detection), but provide inconsistent criteria about which electrodes, and how many, should be deactivated, and without considering how speech information becomes distributed across the electrode array. The present simulation study addresses this issue using computational approaches. Previously validated models were used to generate predictions of speech scores as a function of all possible combinations of active electrodes in a 22-electrode array in three groups of hypothetical subjects representative of relatively better, moderate, and poorer performing CI users. Using high-performance computing, over 500 million predictions were generated. Although deactivation of the poorest encoding electrodes sometimes resulted in predicted benefit, this benefit was significantly less relative to predictions resulting from model-optimized deactivations. This trend persisted when using novel stimuli (i.e. other than those used for optimization) and when using different processing strategies. Optimum electrode deactivation patterns produced an average predicted increase in word scores of 10% with some scores increasing by more than 20%. Optimum electrode deactivation patterns typically included 11 to 19 (out of 22) active electrodes, depending on the performance group. Optimal active electrode combinations were those that maximized discrimination of speech cues, maintaining 80%-100% of the physical span of the array. The present study demonstrates the potential for further improving CI users' speech scores with appropriate selection of active electrodes.

Word perception in noise at different channels in simulated cochlear implant listeners

AIM: To find out effect of different signal-to-noise ratios (SNRs) on word perception at different number of channels.

METHODS: Thirty participants with normal hearing in the age range of 18-25 years (mean age 23.6 years) were involved in the study. For word perception test, there were 28 key-words embedded in sentences comprises of four lists processed for different channels (4, 8 and 32 channel) using AngelSim program at -5, 0 and +5 SNRs. The recorded stimuli were routed through audiometer connected with computer with CD player and presented in free field condition with speakers kept at 0° azimuth in a sound treated room.

RESULTS: Repeated measure ANOVA showed significant main effect across different SNRs at 4 channel, 8 channel and at 32 channel. Further, Bonferroni multiple pairwise comparisons shows significant differences between all the possible combinations (4, 8 and 32 channel) at +5 dB SNR, 0 dB SNR and -5 dB SNR.

CONCLUSION: Present study highlights the importance of more number of channels and higher signal to noise ratio for better perception of words in noise in simulated cochlear implantees.

Electrode migration after cochlear implant surgery: more common than expected?

The overall complication rate of cochlear implant surgery is low and so-called electrode failures (electrode migration, misplacement, etc.,) account for only a minority of all complications. The aim of this study was to explore the prevalence of electrode migration as the cause for increased impedance values and non-auditory stimulation in the basal channels. Within the scope of a quality control process, the cochlear implant database of the Kuopio University Hospital (Finland) was reviewed. Patients with gradual elevation of impedance values and/or non-auditory stimulation of the basal electrode channels were re-examined and cone-beam computed tomography was administered. There were 162 cochlear implant recipients and 201 implanted devices registered in the database. A total of 18 patients (18 devices) were identified having significantly increased impedance values or non-auditory stimulation of the basal electrodes. Cone-beam computed tomography revealed extra-cochlear electrodes in 12 of these patients due to the migration of the electrode array. All extruded electrodes were lateral wall electrodes, i.e., straight electrode arrays (Cochlear CI422 and Med-El devices). The most common feature of electrode migration was the gradual increase of the impedance values in the basal electrodes, even though telemetry could also be unsuspicious. Electrode migration after cochlear implant surgery may be more common than previously reported. At surgery, special attention should be paid to the reliable fixation of the electrode array. This study underlines the importance of postoperative imaging after cochlear implant surgery.

Long-term electrode impedance changes and failure prevalence in cochlear implants

OBJECTIVE

This study assessed the prevalence of electrode failures and electrode impedance measures in Nucleus cochlear implants around initial activation (an average of 16 days after surgery) and after 8 to 12 years of device use.

DESIGN

Retrospective data from the Melbourne Cochlear Implant Clinic was collated and analysed.

STUDY SAMPLE

Included in this study were 232 adults, all of whom were implanted at the clinic between March 1998 and August 2005.

RESULTS

Overall 0.5% of electrodes failed over the entire test period, with 5.6% of devices showing one or more electrode failure. The majority of these failures were recorded by initial activation. The numbers of electrode failures have decreased over time with array type, such that no failures were recorded with the currently available Contour Advance array. Array type was shown to affect electrode impedance at both time points, with the Contour and Contour Advance arrays having significantly higher absolute values than the Banded array. However, the Banded array had significantly higher area-normalized impedances at initial and final measures than the Contour and Contour Advance array.

CONCLUSIONS

A relatively low incidence of electrode failures were recorded for the Nucleus devices of these recipients. Electrode impedance dropped for all array types after 8 to 12 years of device use.

Reduced Cochlear Implant Performance After the Use of Growth Hormone With Regain of Function After Cessation of Growth Hormone Therapy

OBJECTIVE

To assess whether recombinant growth factor (hGH) therapy has an effect on cochlear implant (CI) performance.

PATIENTS

Two pediatric CI recipients (S1, S2) who underwent treatment with hGH for short stature were identified for review. S1 has bilateral labyrinthine dysplasia and received implants at ages 10 months (right) and 4 years 3 months (left). S2 was diagnosed with severe to progressive sensorineural hearing loss bilaterally and received a CI at age 9 years 10 months (left).

INTERVENTION(S)

Case series.

MAIN OUTCOME MEASURE(S)

Cochlear implant, hGH, and speech perception data were collected. Phonetically Balanced Kindergarten (PBK) and Consonant Nucleus Consonant (CNC) word recognition scores were reviewed to assess auditory perception. Electrode impedances, threshold levels, and comfort levels were also reviewed.

RESULTS

After 4 months of hGH, word recognition scores for S1 were observed to decrease from 90 to 72% (right) and were stable at 40% (left). Despite troubleshooting, performance continued to decline bilaterally to 52% (right) and 28% (left), and the decision was made to discontinue hGH. One month after cessation of hGH, word recognition scores began improving to 74% (right) and 68% (left). Word recognition scores for S2 were observed to have decreased from 92% the previous year to 82% after taking hGH for 2 months. Given both our previous experience with S1 and discussions with S2's parents, hGH was discontinued after 10 months of therapy. Two months after cessation of hGH, S2's word recognition had improved to 86% (left).

CONCLUSIONS

Our case studies illustrate that implanted children undergoing treatment with hGH may experience a decrease in speech perception, which recovers after the cessation of treatment. Since hGH use has become more prevalent in recent years, it is important to inquire whether children undergoing, or who have undergone, implantation are receiving hGH so that they may be appropriately monitored.

The Intra-Cochlear Impedance-Matrix (IIM) test for the Nucleus® cochlear implant

To describe the principles and operation of a new telemetry-based function test for the Nucleus

The IIM test measures bipolar impedances between all electrode pairs and employs a normalization procedure based on common ground impedances in order to identify abnormal current paths among electrodes. Six European clinics collected IIM data from a total of 192 devices.

Reproducibility was high between initial and repeat measurements. The normative analysis demonstrated narrow ranges among devices after normalization of impedance data. The IIM is able to identify abnormal current paths that are not evident from standard impedance telemetry and may otherwise only be found utilising average electrode voltage measurements (AEV).

The IIM test was found to be straightforward to perform clinically and demonstrated reproducible data with narrow ranges in normally-functioning devices. Because this test uses a very low stimulation level the IIM test is well suited for children or multiply handicapped CI users who cannot reliably report on their auditory percepts. The new algorithms show potential to improve implant integrity testing capabilities if implemented in future clinical software.

Comprehensive analysis of cochlear implant failure: usefulness of clinical symptom-based algorithm combined with in situ integrity testing

OBJECTIVE

Accurate diagnosis of cochlear implant failures is important for management; however, appropriate strategies to assess possible device failures are not always clear. The purpose of this study is to understand correlation between causes of device failure and the presenting clinical symptoms as well as results of in situ integrity testing and to propose effective strategies for diagnosis of device failure.

STUDY DESIGN

Retrospective case review.

SETTING

Cochlear implant center at a tertiary referral hospital.

PATIENTS

Twenty-seven cases with suspected device failure of Cochlear Nucleus systems (excluding CI512 failures) on the basis of deterioration in auditory perception from January 2000 to September 2012 in the Melbourne cochlear implant clinic.

MAIN OUTCOME MEASURES

Clinical presentations and types of abnormalities on in situ integrity testing were compared with modes of device failure detected by returned device analysis.

RESULTS

Sudden deterioration in auditory perception was always observed in cases with "critical damage": either fracture of the integrated circuit or most or all of the electrode wires. Subacute or gradually progressive deterioration in auditory perception was significantly associated with a more limited number of broken electrode wires. Cochlear implant mediated auditory and nonauditory symptoms were significantly associated with an insulation problem. An algorithm based on the time course of deterioration in auditory perception and cochlear implant-mediated auditory and nonauditory symptoms was developed on the basis of these retrospective analyses, to help predict the mode of device failure. In situ integrity testing, which included close monitoring of device function in routine programming sessions as well as repeating the manufacturer's integrity test battery, was sensitive enough to detect malfunction in all suspected device failures, and each mode of device failure showed a characteristic abnormality on in situ integrity testing.

CONCLUSION

Our clinical manifestation-based algorithm combined with in situ integrity testing may be useful for accurate diagnosis and appropriate management of device failure. Close monitoring of device function in routine programming sessions as well as repeating the manufacturer's integrity test battery is important if the initial in situ integrity testing is inconclusive because objective evidence of failure in the implanted device is essential to recommend explantation/reimplantation.

Validation of minimally invasive, image-guided cochlear implantation using Advanced Bionics, Cochlear, and Medel electrodes in a cadaver model

PURPOSE

Validation of a novel minimally invasive, image-guided approach to implant electrodes from three FDA-approved manufacturers-Medel, Cochlear, and Advanced Bionics-in the cochlea via a linear tunnel from the lateral cranium through the facial recess to the cochlea.

METHODS

Custom microstereotactic frames that mount on bone-implanted fiducial markers and constrain the drill along the desired path were utilized on seven cadaver specimens. A linear tunnel was drilled from the lateral skull to the cochlea followed by a marginal, round window cochleostomy and insertion of the electrode array into the cochlea through the drilled tunnel. Post-insertion CT scan and histological analysis were used to analyze the results.

RESULTS

All specimens ([Formula: see text]) were successfully implanted without visible injury to the facial nerve. The Medel electrodes ([Formula: see text]) had minimal intracochlear trauma with 8, 8, and 10 (out of 12) electrodes intracochlear. The Cochlear lateral wall electrodes (straight research arrays) ([Formula: see text]) had minimal trauma with 20 and 21 of 22 electrodes intracochlear. The Advanced Bionics electrodes ([Formula: see text]) were inserted using their insertion tool; one had minimal insertion trauma and 14 of 16 electrodes intracochlear, while the other had violation of the basilar membrane just deep to the cochleostomy following which it remained in scala vestibuli with 13 of 16 electrodes intracochlear.

CONCLUSIONS

Minimally invasive, image-guided cochlear implantation is possible using electrodes from the three FDA-approved manufacturers. Lateral wall electrodes were associated with less intracochlear trauma suggesting that they may be better suited for this surgical technique.

Outcomes in cochlear implantation: variables affecting performance in adults and children

This article highlights variables that affect cochlear implant performance, emerging factors warranting consideration, and variables shown not to affect performance. Research on the outcomes following cochlear implantation has identified a wide spectrum of variables known to affect pos0timplantation performance. These variables relate to the device itself as well as individual patient characteristics. Factors believed to affect spiral ganglion cell survival and function have been shown to influence postoperative performance. Binaural hearing affects performance. Social and educational factors also affect postoperative performance. Novel variables capable of affecting performance continue to emerge with increased understanding of auditory pathway development and neural plasticity.

Cochlear implants: current status and future potential

This article reviews the current status of cochlear implantation in both adults and children, including expanding candidacy groups, bilateral implantation, advances in speech processing software, internal and external device hardware, surgical techniques and outcomes. Promising advances, novel therapies and evolving concepts are also highlighted in terms of their future impact on clinical outcomes.

Probing the electrode-neuron interface with focused cochlear implant stimulation

Cochlear implants are highly successful neural prostheses for persons with severe or profound hearing loss who gain little benefit from hearing aid amplification. Although implants are capable of providing important spectral and temporal cues for speech perception, performance on speech tests is variable across listeners. Psychophysical measures obtained from individual implant subjects can also be highly variable across implant channels. This review discusses evidence that such variability reflects deviations in the electrode-neuron interface, which refers to an implant channel's ability to effectively stimulate the auditory nerve. It is proposed that focused electrical stimulation is ideally suited to assess channel-to-channel irregularities in the electrode-neuron interface. In implant listeners, it is demonstrated that channels with relatively high thresholds, as measured with the tripolar configuration, exhibit broader psychophysical tuning curves and smaller dynamic ranges than channels with relatively low thresholds. Broader tuning implies that frequency-specific information intended for one population of neurons in the cochlea may activate more distant neurons, and a compressed dynamic range could make it more difficult to resolve intensity-based information, particularly in the presence of competing noise. Degradation of both types of cues would negatively affect speech perception.

Characteristics of malfunctioning channels in pediatric cochlear implants

OBJECTIVES/HYPOTHESIS

To examine the characteristics of pediatric cochlear implant channel malfunction preceding device failure.

STUDY DESIGN

: Retrospective review.

METHODS

All pediatric patients who underwent cochlear implantation at a tertiary academic medical center were reviewed regarding device type, reason for replacement, time to replacement, and timing and pattern of channel faults in failed versus nonfailed devices.

RESULTS

Between 1993 and 2008, 264 pediatric cochlear implantations were performed. With an average 894-day follow-up, the replacement rate was 9.5% (25/264). Reasons for replacement were device failure (6.4%), medical/surgical failure (2.3%), and obsolescence (0.8%). Replacement rates were comparable among Advanced Bionics (13.3%), Cochlear Corporation (6.3%), and MED-EL (10.3%) devices. Fifty-two cochlear implants developed at least one channel fault, and 13 eventually progressed to failure requiring replacement. MED-EL devices comprised 12 of these 13 failures. At the 12-month follow-up interval, one, three, and five channel faults predicted 40%, 75%, and 100% probabilities of eventual electrode failure, respectively. Channels destined to fail demonstrated small, yet statistically significant, impedance elevations 12 months before failure and large elevations 3 months before failure.

CONCLUSIONS

Replacement of cochlear implants in pediatric patients is common and is due to device malfunction about one half of the time. Earlier initial channel fault, earlier subsequent channel faults, adjacent channel faults, and a greater total number of channel faults were associated with the need for replacement surgery. Elevations in a channel's impedance should raise the concern for an impending failure. These predictors can help the cochlear implant team when considering surgery to replace the device.