The Carina© middle ear implant: surgical and functional outcomes

On the battery life of a totally implantable active middle ear device: a retrospective study in a single implanting center

BACKGROUND

Totally-implantable active middle ear devices (AMED) rely on a non-rechargeable battery encased with the implantable sound processor that needs to be replaced with a minor surgical procedure after its depletion.

OBJECTIVES

This study aimed to investigate the most significant factors affecting the implant's battery life.

MATERIALS AND METHODS

The implanted subjects (29 patients) were divided into three groups; group A with 17 patients who underwent one battery change surgery; group B with ten patients who underwent two battery changes; and group C with two patients and three surgeries. The battery life was put in correlation with several variables, including daily use and the auditory threshold.

RESULTS

The battery life ranged from 26 to 67 months, with a mean of 48.93 ± 13.47. Pearson's correlation coefficient revealed that the battery life was statistically correlated only with the mean post-implantation bone conduction thresholds (p-value <.0001).

CONCLUSIONS

Although the non-rechargeable battery system of the AMED under study overcomes the drawbacks of daily charging, it needs to be surgically changed after its depletion. The different rates of battery life were shown to mainly depend on the post-implantation BC thresholds, which in some cases showed a deterioration concerning the pre-implanting values.

Comparison of an Implantable Middle Ear Microphone and Conventional External Microphone for Cochlear Implants: A Clinical Feasibility Study

OBJECTIVES

All commercially available cochlear implant (CI) systems use an external microphone and sound processor; however, external equipment carries lifestyle limitations. Although totally implantable devices using subcutaneous microphones have been developed, these are compromised by problems with soft tissue sound attenuation, feedback, and intrusive body noise. This in vivo pilot study evaluates a middle ear microphone (MEM) that aims to overcome these issues and compares hearing performance with that of an external CI microphone.

DESIGN

Six adult participants with an existing CI were implanted with a temporary MEM in the contralateral ear. Signals from the MEM were routed via a percutaneous plug and cable to the CI sound processor. Testing was performed in the CI microphone and MEM conditions using a range of audiometric assessments, which were repeated across four visits.

RESULTS

Performance of the MEM did not differ significantly from that of the CI on the assessments of Auditory Speech Sounds Evaluation loudness scaling at either 250 or 1000 Hz, or in the accuracy of repeating keywords presented at 70 dB. However, the MEM had significantly poorer aided sound-field thresholds, particularly at higher frequencies (≥4000 Hz), and significantly poorer performance on Arthur Boothroyd words presented at 55 dB, compared with the CI.

CONCLUSION

In this pilot study, the MEM showed comparable performance to that of an external CI microphone across some audiometric assessments. However, performance with the MEM was poorer than the CI in soft-level speech (55 dB) and at higher frequencies. As such, the benefits of MEM need to be considered against the compromises in hearing performance. However, with future development, MEM is a potentially promising technology.

Sensing Devices for Detecting and Processing Acoustic Signals in Healthcare

Acoustic signals are important markers to monitor physiological and pathological conditions, e.g., heart and respiratory sounds. The employment of traditional devices, such as stethoscopes, has been progressively superseded by new miniaturized devices, usually identified as microelectromechanical systems (MEMS). These tools are able to better detect the vibrational content of acoustic signals in order to provide a more reliable description of their features (e.g., amplitude, frequency bandwidth). Starting from the description of the structure and working principles of MEMS, we provide a review of their emerging applications in the healthcare field, discussing the advantages and limitations of each framework. Finally, we deliver a discussion on the lessons learned from the literature, and the open questions and challenges in the field that the scientific community must address in the near future.

Battery Lifespan of an Implantable Middle Ear Device

Background: The Carina system (Cochlear Ltd., Sydney, Australia) is a totally implantable device providing acoustic amplification in adult patients with moderate-to-severe sensorineural or mixed hearing loss. One of the main concerns about such a totally implantable device has been represented by the subcutaneous battery lifespan. The aim of this article is to report the analysis of battery performances in a series of Carina-implanted patients after a long follow up. Methods: In this retrospective study, the technical data of a series of patients implanted with the Carina middle ear implant in our clinic have been analysed, extracting the data from the log of telemetric measures. Results: The mean lifespan cutback was 0.43 h/years (from 0 to 0.71 h/year), with a strong negative significant correlation between the follow-up period and the percentage of battery residual lifespan. Conclusion: The lifespan of the Carina’s battery seems consistent with the manufacturer statement of a pluri-decennial lifespan, avoiding the need of an early surgical substitution and providing a full day of use of the system even after up to 12 years from the implantation.

Results and Quality of Life after Implantation of Active Middle Ear Implants

The provision of implantable hearing aids represents an area with high development and innovation potential. On the one hand, this review article provides an overview of current indication criteria for the treatment with active middle ear implants. On the other hand, outcome parameters as well as functional results after implantation of active middle ear implants are demonstrated and discussed. The focus is mainly placed on audiological results as well as the subjective health status. "Patient Reported Outcome Measures" (PROMs) have become an integral part of the evaluation of hearing implant treatment. Due to low evidence level criteria, the study situation regarding audiological as well as subjective outcome parameters is not satisfactory. The lack of an international consensus on accepted outcome parameters makes a meta-analytical analysis of results immensely difficult. In the studies published to date, patients with sensorineural hearing loss and patients with conductive or mixed hearing loss offered better speech recognition after implantation of an active middle ear implant compared to conventional hearing aids. Current analyses show a significant improvement in general as well as hearing-specific quality of life after implantation of an active middle ear implant. To date, no validated, hearing-specific quality-of-life measurement instruments exist for assessing the success of fitting in children. Especially in children with complex malformations of the outer ear and the middle ear, excellent audiological results were shown. However, these results need to be substantiated by quality-of-life measurements in future.

A Miniature, Fiber-Optic Vibrometer for Measuring Unintended Acoustic Output of Active Hearing Implants during Magnetic Resonance Imaging

Making use of magnetic resonance imaging (MRI) for diagnostics on patients with implanted medical devices requires caution due to mutual interactions between the device and the electromagnetic fields used by the scanner that can cause a number of adverse events. The presented study offers a novel test method to quantify the risk of unintended output of acoustically stimulating hearing implants. The design and operating principle of an all-optical, MRI safe vibrometer is outlined, followed by an experimental verification of a prototype. Results obtained in an MRI environment indicate that the system can detect peak displacements down to 8 pm for audible frequencies. Feasibility testing was performed with an active middle ear implant that was exposed to several pulse sequences in a 1.5 Tesla MRI environment. Magnetic field induced actuator vibrations, measured during scanning, turned out to be equivalent to estimated sound pressure levels between 25 and 85 dB SPL, depending on the signal frequency. These sound pressure levels are situated well below ambient sound pressure levels generated by the MRI scanning process. The presented case study therefore indicates a limited risk of audible unintended output for the examined hearing implant during MRI.

Experimental study of an implantable fiber-optic microphone on human cadavers

In this paper, we present the results of an experimental study about a novel fiber optical vibrometer, aimed to be used as a totally implantable fiber-optic microphone for hearing aids. The sensor head, implanted inside the human cadaver middle ear, detects the amplitude of the incus vibrations, which are produced by an external acoustical source. The probe beam of coherent vertical cavity surface emitting laser (VCSEL) radiation is directed to the incus and the phase-modulated reflected beam is captured and demodulated. The problem of interferometric fading was solved using two quasi-quadrature signals, passively produced by the 3 × 3 single-mode fiber-optic coupler, processed by a special embedded algorithm. The implanted optoelectronic module works with very low-power consumption, performs real-time signal processing and outputs an analogue signal proportional to the incus vibration. The amplitude of the incus vibrations at different sound pressure levels (SPL) from 40 to 90 dB and at frequencies from 100 Hz to 10 kHz were measured by the implanted system. The system was evaluated on five cadaver skulls. The measured amplitudes were in the range of 1 pm to 5 nm, depending on the subjected skull and the applied sound pressure.

[Active hearing implants in chronic otitis media]

In patients with inadequate hearing improvement after tympanoplasty and failure of conventional hearing aid fitting, active hearing implants provide an alternative treatment option. Active middle ear implants function as a vibromechanical bypass of the stiffness and damping effect of a poorly oscillating tympanic membrane and the (reconstructed) ossicular chain. The selection of the hearing system depends on the maximum output levels of the hearing system and the anatomical conditions in mostly multiply operated ears. The development of variable coupling elements for active middle ear implants led to an extension of the indications to include not only purely sensorineural hearing loss but also mixed and conductive hearing loss in patients, as the transducer can now be coupled to the (mobile) stapes or the round window membrane. The article provides an overview of current clinical study results and recommendations on the indications for active hearing implants in patients with chronic otitis media.

Fully Implantable Active Middle Ear Implants After Subtotal Petrosectomy With Fat Obliteration: Preliminary Clinical Results

OBJECTIVES

In patients with chronic middle ear disease, especially after revision surgery for ventilation problems and mixed hearing loss, active middle ear implants may provide an alternative treatment option. The fully implantable active middle-ear implant (FI-AMEI) is designed for implantation in a ventilated mastoid with an intact posterior canal wall. Until now, there have been no reports on audiometric results after implantation of a FI-AMEI in a fat-obliterated cavity after subtotal petrosectomy (SPE).

STUDY DESIGN

Retrospective case review.

SETTING

Tertiary referral center.

PATIENTS

Twelve patients were included after numerous previous tympanoplasty surgeries for severe mixed hearing loss and FI-AMEI implantation.

INTERVENTION

In five patients, the FI-AMEI was implanted in a cavity, with fat obliteration, after SPE. Seven patients received FI-AMEI implantation after intact canal wall (ICW) surgery.

MAIN OUTCOME MEASURE(S)

Audiometric results (pure-tone audiometry, Freiburger monosyllables) are demonstrated for 12 patients after an observation period of 3 months.

RESULTS

The improvement in monosyllable score was 40 to 85% for the 12 patients. Free-field-aided thresholds showed high heterogeneity.

CONCLUSION

FI-AMEI implantation combined with SPE provides an alternative approach to hearing rehabilitation to non-FI-AMEI implantation. Studies with a high number of patients and long-term observation periods are necessary to statistically verify these results.

[Use of the Carina active middle ear implant in otosclerosis patients]

Patients with otosclerosis can suffer from different grades of combined hearing loss. In addition to surgery (stapedectomy), conventional hearing aids can be used in the treatment of otosclerosis. In cases of severe conductive components in addition to sensorineural hearing loss, treatment with normal hearing aids can be difficult or impossible. In these patients, implantable hearing systems such as cochlear implants represent a possible alternative. The totally implantable Carina middle ear system can be used in patients with even high-grade sensorineural hearing loss. Based on two exemplary cases, the option of using the Carina system in otosclerosis patients and post-implantation results are reported.

Implantable Hearing Aids: Where are we in 2020?

Beginning in the late 20th century, implantable hearing aids were developed and used as an alternative for individuals who were unable to tolerate conventional hearing aids. Since that time, several devices have been developed, with four currently remaining on the international market (Med-el Vibrant Soundbridge, Envoy Esteem, Ototronix MAXUM, and Cochlear Carina). This review will briefly examine the history of middle ear implant development, describe current available devices, evaluate the benefits and limits of the technology, and consider the future directions of research in the field of implantable hearing aids.

In-situ sensitivity of a totally-implantable microphone

One of the key components of fully-implantable hearing devices is the implantable microphone. A crucial parameter when characterizing implantable microphones is the acoustic sensitivity, as it is one of the input parameters for the fitting algorithm and influences the achievable gain. The aim of our study was to investigate the sensitivity of an implanted subcutaneous microphone over time to answer two research questions: (1) How does the sensitivity change once the microphone is implanted under the skin (pre-op versus in-situ)? and (2) How does the sensitivity change from short-term to mid-term? We have measured the in-situ microphone sensitivity in three subjects implanted with a fully-implantable active middle ear implant from 2 weeks up to 20 weeks after implantation with a research software. The microphone sensitivity changed after implantation with clinically relevant changes around the resonance frequency of the microphone. Based on our results, it is essential to measure the in-situ microphone sensitivity at the time of initial fitting of the implant. Once implanted no clinically relevant changes in the microphone sensitivity were observed over time, with a clear decrease in variability over time.

Binaural hearing restoration with a bilateral fully implantable middle ear implant

AIM

The fully implantable middle ear implant (C-FI-MEI) is designed for patients with moderate-to-severe sensorineural hearing loss or those with mixed hearing loss. To analyze the audiological post-operative results of subjects bilaterally implanted with C-FI-MEI.

MATERIALS AND METHODS

Retrospective study: 14 patients with bilateral, moderate-to-severe, sensorineural or mixed hearing loss were treated. This clinical sample included 14 cases bilaterally implanted (13 sequentially, 1 simultaneously). The evaluation at each follow-up after surgery included otologic examination, a structured interview, and different audiological tests composed of pure tone audiometry, speech in quiet and in noise test, and localization task. The mean follow-up was 67.2 ± 33 months.

RESULTS

There were no significant differences between pre and post-operative pure tone averages. The patients showed no significant differences between pre-operatively aided and C-FI-MEI implant-aided conditions in terms of word recognition score. Speech perception in noise under different loudspeaker arrangements and localization tests demonstrated a binaural advantage in bilaterally implanted patients. The mean daily use time was 17.4 and 16.7 h, respectively, for right and left side.

CONCLUSION

The results for the 14 patients, bilaterally implanted with C-FI-MEI, suggest that bilateral implantation of fully implantable middle ear hearing devices is an effective procedure.

LEVEL OF EVIDENCE

4.

Intraoperative determination of coupling efficiency of Carina® middle ear implant by means of auditory evoked potentials

OBJECTIVE

The Carina^® implant system is a fully implantable active middle ear implant, which can be coupled to various structures in the middle ear, depending on the nature of the hearing loss and the middle ear anatomy. Currently, there is only one method for determining the coupling efficiency of the actuator of this implant system, and this is limited to incus coupling.

DESIGN

The proposed method is based on the intraoperative recording and evaluation of auditory brainstem responses (ABRs) while directly stimulating the hearing system via the actuator. The acoustic stimulation was achieved using an optimised broadband chirp stimulus (CE-Chirp^®).

STUDY SAMPLES

This study included 10 subjects having moderate to severe sensorineural or mixed hearing loss.

RESULTS

The intraoperative ABR measurements show, that it is possible to derive reliable AEP thresholds via the actuator of the implant. The ABR thresholds correlate well with preoperative BC PTA4 thresholds (r = 0.87) while the postoperative OC-direct thresholds (in situ audiogram via the implant) correlate with r = 0.77.

CONCLUSION

The results demonstrated that the direct actuator stimulation allow for reliable intraoperative ABR measurements and that the proposed method can be used to estimate the coupling efficiency of the actuator and facilitate its positioning.

A Transcutaneous Active Middle Ear Implant (AMEI) in Children and Adolescents: Long-term, Multicenter Results

OBJECTIVE

Evaluation of the long-term safety and performance of an active middle ear implant (AMEI) in the treatment of hearing loss in children and adolescents with a primary focus on improvement in speech discrimination.

STUDY DESIGN

Prospective, multicentric, single-subject repeated-measures design in which each subject serves as his or her own control.

SUBJECTS

Thirty-one pediatric subjects aged 5 to 17 years.

INTERVENTION

Implantation of an active middle ear implant.

METHODS

Improvement in word recognition scores, speech reception thresholds (SRT) in quiet and noise, in addition to air conduction, bone conduction, and sound field thresholds were evaluated in two age groups.

RESULTS

Residual hearing did not change over time and speech intelligibility significantly improved and remained stable after 36 months. Children aged 5 to 9 improved in WRS from 21.92 to 95.38% and in SRT in quiet and in noise respectively from 62.45 dB SPL (sound pressure level) and +1.14 dB SNR to 42.07 dB SPL and -4.45 dB SNR. Adolescents aged 10 to 17 improved in WRS from 12.78 to 84.71% and in SRT in quiet and in noise respectively from 63.96 dB SPL and +3.32 dB SNR to 35.31 dB SPL and -4.55 dB SNR.

CONCLUSIONS

The AMEI, under investigation, is a safe treatment for children and adolescents, and significantly improved audiological performance that remains stable on the long-term scale (up to 36 mo postimplantation). In general, all adult-related issues and questions regarding safety and performance can also be applied to the pediatric population, as no apparent specific issues developed.

Surgical and audiological outcomes of a fully implantable middle ear implant: early results from a retrospective multicentre study

PURPOSE

This paper reports the surgical and audiological outcomes of a large series of patients who received a fully implantable middle ear implant (MEI): carina (Cochlear, Australia).

METHODS

This is a multicentre retrospective study involving three tertiary referral centres. Patient data were collected for the first 42 consecutive patients who were fitted with the MEI between 2014 and 2019 (Sheffield from February 2017 to January 2019; São Paulo from April 2015 to September 2017; Porto from December 2014 to May 2017). The main outcome measures included surgical results, free field speech testing with speech recognition thresholds (SRT) and audiological gain.

RESULTS

There was one major complication due to infection resulting in a brain abscess and explantation of the device. Three other patients had minor skin infections; no other complications were reported. Results show a functional gain of 19.5 dB (p < 0.05) with the MEI versus unaided condition. SRT improved from 57.4 dB to 44.6 dB with the MEI (p < 0.05).

CONCLUSIONS

This fully implanable active MEI offers a reliable option for patients with moderate-to-severe sensorineural or mixed hearing losses especially for those do not tolerate or cannot use conventional hearing aids. It provides significant improvement in hearing as shown in the audiological outcomes. The surgery is relatively straightforward but there is a steep learning curve. The devices are well tolerated by all patients.

Stability of the standard incus coupling of the Carina middle ear actuator after 1.5T MRI

Limited data is available concerning the safety of active middle ear implants (AMEI) during Magnetic Resonance Imaging (MRI). Measurements in temporal bones are the gold standard for preclinical assessment of device safety. In this study the coupling stability of an actuator as used in a fully implantable AMEI was determined in temporal bones. Eleven temporal bones were implanted with the actuator according to the manufacturer’s surgical guidelines. The actuator was coupled on the incus short process as recommended for sensorineural hearing loss. Temporal bones were exposed 10 times to the MRI magnetic field by entering the MRI suite in a clinically relevant way. Computed Tomography (CT) images were acquired before and after the experiment to investigate the risk of actuator dislocation. Based on the electrical impedance of the actuator, the loading of the actuator to the incus was confirmed. Relative actuator displacement was determined on the CT images by comparing the initial with the final actuator position in 3D space. Impedance curves were analyzed after each exposure to check the loading of the actuator to the ossicles. Analysis of CT images with a 0.30.6 mm in-plane resolution indicate no actuator displacement. The maximum detected change in impedance for all actuators was 8.43 Ω at the actuator’s resonance frequency. Impedance curves measured when the actuator was retracted from the short process after the experiment still indicate the presence of a clear resonance peak. No actuator displacement or dislocation could be detected in the analysis of CT images and the measured impedance curves. Impedance curves obtained when the actuator was retracted from the incus short process still show a clear resonance peak, indicating the device is still functional after the MRI exposures.

Totally Implantable Active Middle Ear Implants

The Envoy Esteem and the Carina system are the 2 totally implantable hearing devices. The Esteem is designed for patients with bilateral moderate to severe sensorineural hearing loss who have an unaided speech discrimination score of greater than and equal to 40%. The Carina system is designed for patients with moderate to severe sensorineural hearing loss or those with mixed hearing loss. The Esteem offers a technologically advanced method to provide improvements in hearing and is available in the United States, whereas the Carina system is currently not available in the United States.

Air- and Bone-Conducted Sources of Feedback With an Active Middle Ear Implant

OBJECTIVES

Active middle ear implants (AMEI) have been used to treat hearing loss in patients for whom conventional hearing aids are unsuccessful for varied biologic or personal reasons. Several studies have discussed feedback as a potential complication of AMEI usage, though the feedback pathway is not well understood. While reverse propagation of an acoustic signal through the ossicular chain and tympanic membrane constitutes an air-conducted source of feedback, the implanted nature of the device microphone near the mastoid cortex suggests that bone conduction pathways may potentially be another significant factor. This study examines the relative contributions of potential sources of feedback during stimulation with an AMEI.

DESIGN

Four fresh-frozen, hemi-sectioned, human cadaver specimens were prepared with a mastoid antrostomy and atticotomy to visualize the posterior incus body. A Carina active middle ear implant actuator (Cochlear Ltd., Boulder, CO) was coupled to the incus by two means: (1) a stereotactic arm mounted independently of the specimen and (2) a fixation bracket anchored directly to the mastoid cortical bone. The actuator was driven with pure-tone frequencies in 1/4 octave steps from 500 to 6000 Hz. Acoustic sound intensity in the ear canal was measured with a probe tube microphone (Bruel & Kjær, Nærum, Denmark). Bone-conducted vibration was quantified with a single-axis laser Doppler vibrometer (Polytec Inc., Irvine, CA) from both a piece of reflective tape placed on the skin overlying the mastoid and a bone-anchored titanium screw and pedestal (Cochlear Ltd., Centennial, CO) implanted in the cortical mastoid bone.

RESULTS

Microphone measurements revealed ear-canal pressures of 60-89 dB SPL, peaking in the frequency range below 2 kHz. Peak LDV measurements were greatest on the mastoid bone (0.32-0.79 mm/s with mounting bracket and 0.21-0.36 mm/s with the stereotactic suspension); peak measurements on the skin ranged from 0.05 to 0.15 mm/s with the bracket and 0.03 to 0.13 mm/s with stereotactic suspension.

CONCLUSION

AMEI produce both air- and bone-conducted signals of adequate strength to be detected by the implanted device microphone, potentially resulting in reamplification. Understanding the relative contribution of these sources may play an important role in the development of targeted mitigation algorithms, as well as surgical techniques emphasizing acoustic isolation.

Neurophysiology and neural engineering: a review

Neurophysiology is the branch of physiology concerned with understanding the function of neural systems. Neural engineering (also known as neuroengineering) is a discipline within biomedical engineering that uses engineering techniques to understand, repair, replace, enhance, or otherwise exploit the properties and functions of neural systems. In most cases neural engineering involves the development of an interface between electronic devices and living neural tissue. This review describes the origins of neural engineering, the explosive development of methods and devices commencing in the late 1950s, and the present-day devices that have resulted. The barriers to interfacing electronic devices with living neural tissues are many and varied, and consequently there have been numerous stops and starts along the way. Representative examples are discussed. None of this could have happened without a basic understanding of the relevant neurophysiology. I also consider examples of how neural engineering is repaying the debt to basic neurophysiology with new knowledge and insight.

A Retrospective Multicentre Cohort Review of Patient Characteristics and Surgical Aspects versus the Long-Term Outcomes for Recipients of a Fully Implantable Active Middle Ear Implant

OBJECTIVE

To summarise treatment outcomes compared to surgical and patient variables for a multicentre recipient cohort using a fully implantable active middle ear implant for hearing impairment. To describe the authors' preferred surgical technique to determine microphone placement.

STUDY DESIGN

Multicentre retrospective, observational survey.

SETTING

Five tertiary referral centres.

PATIENTS

Carina recipients (66 ears, 62 subjects) using the current Cochlear® Carina® System or the legacy device, the Otologics® Fully Implantable Middle Ear, with a T2 transducer.

METHODS

Patient file review and routine clinical review. Patient outcomes assessed were satisfaction, daily use and feedback reports at the first fitting and ≥12 months after implantation. Descriptive and statistical analysis of correlations of variables and their influence on outcomes was performed. Independently reported preferred methods for microphone placement are collectively summarised.

RESULTS

The average implant experience was 3.5 years. Satisfaction increased significantly over time (p < 0.05). No correlation with covariates examined was observed. Feedback significantly decreased over time, showing a significant correlation with microphone location, primary motivation, gender, age at implantation, and contralateral hearing aid use (p < 0.05). Patient satisfaction was inversely correlated with reports of system feedback (p < 0.05). The implantable microphone was most commonly on the posterior inferior mastoid line, in 42/66 (65%) cases, correlating with less likelihood for feedback and consistent with author surgical preference.

CONCLUSION

Carina recipients in this study present as satisfied consistent daily users with very few reports of persistent feedback. As microphone location is an influencing factor, a careful surgical consideration of microphone placement is required. The authors prefer a posterior inferior mastoid line position whenever possible.