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Cochlear Implants

CIs with Known Potential for Failure: Monitoring and Management in Children

Lewkowitz, Ashleigh AuD; Harris, Jennifer AuD; Licameli, Greg MD

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doi: 10.1097/01.HJ.0000717152.71538.9d
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The Advanced Bionics (AB) HiRes Ultra series of cochlear implants (CIs) was first introduced to the U.S. market in 2016, initially with the mid-scala electrode array and later with the Slim J electrode array; the HiRes Ultra 3D models of both arrays were introduced in 2019. After observing a higher-than-expected failure rate with the Ultra/Ultra 3D devices, AB announced a voluntary field corrective action on the Ultra and Ultra 3D internal devices on Feb. 18, 2020, and removed all non-implanted devices from circulation.1 Per AB, an issue was identified with moisture ingress into the electrode portion of the internal device resulting in interruptions in stimulation and degraded hearing performance, potentially necessitating the internal device(s) to be replaced via revision surgery. AB describes a clinical marker of this issue to be low impedance (less than or equal to 3.5 kOhms) on several (four or more) electrodes, typically in the basal region (high-frequency portion) of the array. Associated changes in neural response imaging (NRI) responses, audibility, loudness growth, and speech understanding may also be present.2 Changes in responsiveness to high-frequency speech sounds such as /s/ and /f/ may be observed by caregivers, interventionists, and educators working with the CI recipient. While the voluntary field corrective action removed all non-implanted devices from circulation, attention has now turned to those devices already implanted and how to best identify problematic implants and manage them; specifically, how to do so in a pediatric population.

Figure
Figure:
Figures 1A & 1B. Examples of decreased impedances. A (top): Annual impedances over four years in an affected Ultra device; the most recent measurement in bold. B (bottom): Annual impedances over three years in an affected Ultra device; the most recent measurement in bold. Audiology, cochlear implants, health, technology.
Figure
Figure:
Figures 2A & 2B. Examples of atypical NRI morphology observed in an affected device on two different electrodes with decreased impedances. Audiology, cochlear implants, health, technology.

Along with changes in objective measures including impedances and NRI, a common finding in a failing device is a decrease in performance as measured by soundfield detection thresholds for warble tones and/or speech recognition measures. Adult recipients may be able to monitor the device, provide qualitative information regarding sound quality, and alert the audiologist when they perceive any decrease in performance. However, very young children or children who are not developmentally able to perform these measures are unable to provide qualitative feedback, making it difficult for clinicians to identify a faulty device and when a device should be replaced. For these patients, a more aggressive monitoring approach and device replacement guideline are needed to minimize the duration of compromised hearing, especially in early language-learning years. Clinicians must also be mindful of separate ear monitoring in children with bilateral CIs since symptoms of a failing device on one side can be masked by a well-functioning device in the contralateral ear.

In this paper, we present unique clinical findings that audiologists should recognize as a potential indication of a failure in these particular devices. Additionally, we're sharing a monitoring algorithm for testing patients over time, which is critical to supporting good speech and language outcomes, particularly in very young children.

IDENTIFICATION OF AFFECTED DEVICES

Affected AB HiRes Ultra/Ultra 3D devices typically exhibit at least one of the following problems:

  • A low flat pattern of impedance (<3.5 kOhms) on several adjacent electrodes, typically in the basal region of the electrode array
  • Loss of NRI responses
  • Poorer than previous or poorer than typical high-frequency detection thresholds, which can sometimes be temporarily improved through electrode deactivation and reallocation of frequencies
  • Decreased speech recognition scores, which can also sometimes be temporarily improved through electrode deactivation and reallocation of frequencies

OBSERVATIONS

Recipients tend to exhibit changes in impedance patterns prior to loss of NRI and/or decrease in performance. While we can sometimes improve sound detection thresholds and speech recognition through deactivation of affected electrodes, we observed that this approach has not been sustainable in our population. For some recipients, as much as 50 percent of the electrode array has ultimately needed to be disabled and a point reached when no amount of programming adjustment can support a return to previous detection thresholds and/or speech recognition scores. To best organize our identification and management efforts for our pediatric population, we have implemented the plan below, with distinct paths for children developmentally able to complete speech perception testing and those not yet able to do so.

AUDIOLOGIC MANAGEMENT PLAN

This detailed management plan developed at the Boston Children's Hospital starts with identifying three problems: (1) low flat impedances, especially in the basal end, (2) an absent NRI where previous responses existed, and (3) poorer than expected booth thresholds and/or decreased speech testing performance in children who can participate.

All recipients not exhibiting a pattern of low flat impedances and absent NRI upon SoundWave file review should be seen for updated baseline impedances and NRI on all electrodes within six months of file review.

  • Serial impedance, NRI, and performance monitoring every three months as long as the pattern is not observed.
  • If stable for three years, the monitoring interval is increased to every six months.

Recipients who do exhibit the pattern upon SoundWave file review should be seen for updated baseline impedances, NRI on all electrodes, performance testing, and integrity testing (IT) as soon as possible and no longer than four to six weeks after the review.

As a general guideline, if IT reveals atypical electrode function, the patient is managed in the short term by mapping changes (i.e., disabling atypical electrodes, use of SPAN as applicable) verified by performance testing depending on the developmental age of the child. Discussion of revision is initiated with the family.

For a child who can undergo reliable word-level performance testing using recorded materials:

  • IT is within normal limits: Continue serial monitoring of impedances, NRI, and performance testing in two-month intervals, and repeat IT in three to four months or sooner if new concerns arise. If no further abnormality or concern is noted after three years, the monitoring interval is increased to four months.
  • IT reveals atypical electrode function, but performance can be maintained via mapping changes: Monitor as above and begin a proactive discussion of revision with the child's family.
  • IT reveals atypical electrode function, and performance cannot be maintained through mapping changes: Move forward with revision.

For a child who is not yet capable of reliable word-level performance testing using recorded materials:

  • IT is within normal limits, but two of three problem items are noted: Move forward with revision.
  • IT is within normal limits with only one problem item noted: The next steps are determined by how many electrodes must be disabled to maintain booth thresholds.
  • If four or more electrodes must be disabled: Move forward with revision.
  • If fewer than four electrodes must be disabled: Continue with serial monitoring at two-month intervals, and repeat IT after three to four months. If stable for three years, the monitoring interval is increased to every six months.
  • IT reveals atypical electrode function on any number of electrodes: Move forward with revision.

CHALLENGES & FUTURE DIRECTIONS

We acknowledge the inherent challenges that arise with the implementation of a management plan that necessitates more frequent clinic visits for patients and families; however, we also recognize the importance of ensuring appropriate monitoring intervals for HiRes Ultra/Ultra 3D internal devices given the known potential for moisture ingress issues that may develop over time. Specific areas of concern include the feasibility of seeing patients more frequently, especially those living at great distances; possible out-of-pocket costs to families for more frequent visits; the need for ongoing performance monitoring outside of the clinic; and the increased strain on audiologists’ schedules from accommodating more frequent visits in addition to current caseload. We are collaborating with educational audiologists and local mapping centers closer to patients’ homes to carry out impedance monitoring, reaching out to early intervention (EI) providers and teachers of the deaf/hard of hearing (ToD/HH) to enlist their assistance in monitoring for changes in performance, and manipulating clinic schedules as needed to accommodate additional patient visits.

Ideally, a system can be established where basic monitoring of impedances and NRI could be done remotely, especially for patients living a great distance from our center. Parents, EI providers, ToD/HHs can be educated on specific ways to monitor ear-specific performance at home and report changes or concerns to the managing audiologist. The clinical management plan we have developed for the AB HiRes Ultra/Ultra 3D devices can be modified as needed by cochlear implant centers to address future device issues as they arise.

Timely assessment and monitoring of device function and performance in children with AB HiRes Ultra/Ultra 3D devices are imperative to limiting and mitigating any potential developmental impacts of prolonged listening with a failed device. For children with HiRes Ultra/Ultra 3D devices, clinicians should have a low threshold for requesting integrity testing and an even lower threshold for moving forward with revision should integrity testing reveal any abnormal electrode function. Depending on the developmental abilities of the child in question, consideration of soundfield detection thresholds and speech recognition testing performance and the ability to maintain that performance through mapping adjustments should also be strongly considered when discussing revision. For children unable to participate in the assessment of performance, any atypical findings in integrity testing should trigger prompt revision surgery.

Acknowledgment: The authors would also like to acknowledge Amanda Griffin, AuD, PhD, and Derek Stiles, PhD, for their contributions in editing this manuscript.

REFERENCES

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