Early clinical results: SOUNDTEC implantable hearing device phase II study

New Approach for Implantable Hearing Aids: A Feasibility Study

The objective of this study was to test the feasibility of a new kind of implantable hearing device based on a cerebrospinal fluid hydroacoustic pathway by which sound waves are conducted from the dura mater to the inner ear by cerebrospinal fluid. In this prospective animal study, a piezoelectric bimorph was implanted into 2 guinea pigs and 1 dog between the skull bone and the dura at the parietal area. The bimorph was connected transdermally by wires to a click generator. The auditory brain stem response was recorded after stimulation of the piezoelectric device by the click generator. In the 3 animals, the auditory brain stem response could be recorded in response to a stimulus intensity of 135 dB peak equivalent (pe) sound pressure level (SPL; instrument setting), corresponding to 3.8 V activating the device. The auditory brain stem response disappeared during white noise masking, proving that the origin of the response was in the inner ear. The threshold was 125 and 115 dB pe SPL in the 2 guinea pigs and 135 dB pe SPL in the dog (instrument setting). We conclude that transmission of sound waves by a cerebrospinal fluid hydroacoustic pathway to the inner ear is possible. Such a device would have advantages over more traditional implantable hearing devices: it would not be necessary to couple it to the ossicular chain, and it could be used in patients with infected middle ears.

Middle ear implants for rehabilitation of sensorineural hearing loss: a systematic review of FDA approved devices

OBJECTIVE

To systematically review the safety and efficacy of the 3 Food and Drug Administration-approved middle ear implant (MEI) systems currently in use for the rehabilitation of sensorineural hearing loss.

DATA SOURCES

MEDLINE and Cochrane Library databases were systematically searched by 2 independent reviewers.

STUDY SELECTION

An initial search yielded 3,020 articles that were screened based on title and abstract. A full manuscript review of the remaining 80 articles was performed, of which 17 unique studies satisfied inclusion criteria and were evaluated.

DATA EXTRACTION

Variables including functional gain, speech recognition score improvement, audiometric threshold shift following surgery, adverse events, and patient reported outcome measures were recorded. Study quality was appraised according to author conflict of interest, prospective or retrospective study design, inclusion criteria, number of patients, proper use of study controls, outcome measures reported, length of follow-up, and level of evidence.

DATA SYNTHESIS

Heterogeneous outcome reporting precluded meta-analysis; instead a structured review was performed using best available data.

CONCLUSION

The majority of studies evaluating the safety and efficacy of MEIs are retrospective in nature with limited follow-up. To date, no prospective randomized controlled trial exists comparing contemporary air conduction hearing aid performance and MEI outcomes. Based on available data for patients with sensorineural hearing loss, functional gain and word recognition improvement seems similar between conventional hearing aids and MEIs, whereas patient-perceived outcome measures suggest that MEIs provide enhanced sound quality and eliminate occlusion effect.

The envoy® totally implantable hearing system, st. Croix medical

The Totally Implantable Envoy® System is currently undergoing clinical trials in both the United States and Europe. The fully implantable hearing device is intended for use in patients with sensorineural hearing loss. The device employs piezoelectric transducers to sense ossicle motion and drive the stapes. Programmable signal processing parameters include amplification, compression, and variable frequency response. The fully implantable attribute allows users to take advantage of normal external ear resonances and head-related transfer functions, while avoiding undesirable earmold effects. The high sensitivity, low power consumption, and high fidelity attributes of piezoelectric transducers minimize acoustic feedback and maximize battery life (Gyo, 1996; Yanagihara, (1987) and 2001). The surgical procedure to install the device has been accurately defined and implantation is reversible.

Implantable hearing devices: the Ototronix MAXUM system

For many hearing-impaired individuals, the benefits of conventional amplification may be limited by acoustic feedback, occlusion effect, and/or ear discomfort. The MAXUM system and other implantable hearing devices have been developed as an option for patients who derive inadequate assistance from traditional HAs, but who are not yet candidates for cochlear implants. The MAXUM system is based on the SOUNDTEC Direct System technology, which has been shown to provide improved functional gain as well as reduced feedback and occlusion effect compared to hearing aids. This and other implantable hearing devices may have increasing importance as future aural rehabilitation options.

Efficacy of the active middle-ear implant in patients with sensorineural hearing loss

Introduction:

This systematic review aims to advise on the effectiveness of the active middle-ear implant in patients with sensorineural hearing loss, compared with external hearing aids.

Methods:

A systematic search of several electronic databases, including PubMed and Embase, was used to identify relevant studies for inclusion.

Results:

Fourteen comparative studies were included. Nine studies reported on the primary outcome of functional gain: one found that the middle-ear implant was significantly better than external hearing aids (p < 0.001), while another found that external hearing aids were generally significantly better than middle-ear implants (p < 0.05). Six of the seven remaining studies found that middle-ear implants were better than external hearing aids, although generally no clinically significant difference (i.e. ≥10 dB) was seen.

Conclusion:

Generally, the active middle-ear implant appears to be as effective as the external hearing aid in improving hearing outcomes in patients with sensorineural hearing loss.

Passive and active middle ear implants

Besides eradication of chronic middle ear disease, the reconstruction of the sound conduction apparatus is a major goal of modern ear microsurgery. The material of choice in cases of partial ossicular replacement prosthesis is the autogenous ossicle. In the event of more extensive destruction of the ossicular chain diverse alloplastic materials, e.g. metals, ceramics, plastics or composits are used for total reconstruction. Their specialised role in conducting sound energy within a half-open implant bed sets high demands on the biocompatibility as well as the acoustic-mechanic properties of the prosthesis. Recently, sophisticated titanium middle ear implants allowing individual adaptation to anatomical variations are widely used for this procedure. However, despite modern developments, hearing restoration with passive implants often faces its limitations due to tubal-middle-ear dysfunction. Here, implantable hearing aids, successfully used in cases of sensorineural hearing loss, offer a promising alternative. This article reviews the actual state of affairs of passive and active middle ear implants.

A totally implantable hearing system--design and function characterization in 3D computational model and temporal bones

Implantable middle ear hearing devices are emerging as an effective technology for patients with mild to moderately severe sensorineural hearing loss. Several devices with electromagnetic or piezoelectric transducers have been investigated or developed in the US and Europe since 1990. This paper reports a totally implantable hearing system (TIHS) currently under investigation in Oklahoma. The TIHS consists of implant transducer (magnet), implantable coil and microphone, DSP-audio signal processor, rechargeable battery, and remote control unit. The design of TIHS is based on a 3D finite element model of the human ear and the analysis of electromagnetic coupling of the transducer. Function of the TIHS is characterized over the auditory frequency range in three aspects: (1) mass loading effect on residual hearing with a passive implant, (2) efficiency of electromagnetic coupling between the implanted coil and magnet, and (3) functional gain of whole unit in response to acoustic input across the human skin. This paper focuses on mass loading effect and the efficiency of electromagnetic coupling of TIHS determined from the FE model of the human ear and the cadaver ears or temporal bones. Some preliminary data of whole unit function are also presented in the paper.

Integrating the patient's perspective into device evaluation trials

Innovations in medical device technology have greatly expanded the range of therapeutic options available to physicians and their patients. The understanding of treatment effects from the patient's perspective is an essential component of a comprehensive assessment of any new therapy, including medical devices. The term "patient-reported outcomes" (PROs) has been growing in use to refer to a cluster of variables such as health-related quality of life, symptoms, physical functioning, psychological well-being, treatment satisfaction, and treatment preferences. As in drug trials, the use of PROs in device evaluation has several methodological challenges, ranging from general concerns about interpretation, to more specific issues related to study design and regulatory approval (use of PROs as primary end points, incorporation in labeling, and product promotion). Successful approaches for integrating PROs into device evaluation trials include the careful selection of appropriate, interpretable PRO end points, accounting for possible confounding factors, and the use of alternatives to placebo-controlled trial designs, such as single-arm pre-post, observational, and registry studies, when the use of placebo control groups is not feasible. This article discusses the potential value and difficulties in measuring PROs in device studies.

Magnetic Resonance Imaging Compatibility and Safety of the SOUNDTEC Direct System

OBJECTIVE/HYPOTHESIS

The purpose of this study was to evaluate magnetic resonance imaging (MRI) compatibility and safety of an electromagnetic implanted hearing device (the SOUNDTEC Direct System; SOUNDTEC, Inc., Oklahoma City, OK) implant during a 0.3-Tesla open MRI imaging examination of the head and neck and to develop an MRI protocol that maximizes patient safety while minimizing the need for implant removal. The current literature regarding MRI compatibility of implantable hearing devices was reviewed.

STUDY DESIGN

Linear and torsional forces, heating, and implant magnetization were evaluated in vitro. Implanted fresh-frozen human temporal bones were used to evaluate image distortion. A prospective study of 11 volunteers previously implanted with the SOUNDTEC Direct System was conducted to evaluate MRI compatibility and safety. A MEDLINE search of the literature between 1980 and July 2005 was reviewed to summarize MRI compatibility testing of implantable hearing devices.

METHODS

Torsional and linear forces experienced by eight implant magnets were measured using calibrated neurologic Von Frey Hairs and compared with finite element analysis predictions as well as forces required to separate the incudostapedial joints of 12 fresh-frozen human temporal bones. Implant heating was determined by measuring the temperature change of eight implant vials compared with saline controls immediately after a head MRI scan. Implant magnetization was evaluated after repeated exposure to a 0.3-Tesla magnetic field. An 11-patient prospective study was performed to evaluate MRI compatibility in a 0.3-Tesla open MRI environment using adult volunteers previously implanted with the SOUNDTEC Direct System. A modified MRI protocol was developed to maximize patient safety. Each individual underwent an audiometric and otologic examination immediately before and after MRI.

RESULTS

Peak linear force at the MRI entry measured 0.5 g +/- 0.2 standard deviation (SD). Maximum torque occurred at isocenter and measured 11.4 g-cm +/- 1.2 SD. The mean torque required to separate the incudostapedial joint was 33.8 g-cm +/- 20.4 SD. The average increase in temperature of the eight implant vials was 0.45 degrees C +/- 0.11 SD, whereas the increase in temperature of the three saline controls measured 0.47 degrees C +/- 0.11 SD. The average change in magnetic flux density of the 14 implant magnets tested was 22.0 gauss. Maximum image distortion occurred during the gradient echo sequence and measured 8.6 cm in diameter with a volume of 5,096 mm. Eleven patients completed a total of 12 head, one shoulder, and three lumbar 0.3-Tesla open MRI scans without patient- or device-related complications other than degradation of the MR image. There was no report of discomfort, tinnitus, dizziness, change in hearing, or change in device performance. All post-MRI changes in pure-tone thresholds, speech discrimination, soundfield thresholds, and aided soundfield thresholds were within the range of test-retest variability.

CONCLUSION

When considering MRI of implantable ferromagnetic hearing devices, issues related to mechanical forces, implant heating, current induction, implant demagnetization, image degradation, and acoustic trauma must be considered. The SOUNDTEC Direct System is both MRI-compatible and safe in a 0.3-Tesla open MRI environment when a modified protocol is used. Degradation of the head MRI image may impair visualization of the ipsilateral temporal bone and adjacent structures within a 2.5- to 4.3-cm radius of the implant and is minimized by using a fast spin echo sequence.

In Vitro Model for Intraoperative Adjustments in an Implantable Hearing Aid (MET)

OBJECTIVE

Assessment of the optimal static preloading of Otologics Middle Ear Transducer (MET) Ossicular Stimulator, when coupled to the incus.

BACKGROUND

The MET Ossicular Stimulator is a partially implantable electromagnetic middle ear hearing device that transmits vibrations to the ossicular chain. The vibration patterns were measured with laser-Doppler vibrometry.

STUDY DESIGN

Experimental.

MATERIAL

We used three human cadaveric temporal bones (TB) and one MET ossicular stimulator.

METHODS

Laser-Doppler vibrometry was used for the selection of TBs. The cochlea was subsequently extirpated from the posterior side to measure the vibrational patterns (VP) of the footplate. Three TBs with different VP were selected based on data obtained from volunteers with normal hearing (n = 110): one TB with a VP larger than +1 SD, one TB with a VP in the range of +/-1 SD, and 1 TB with a VP smaller than -1 SD. Transfer functions were calculated between VP of the measurement points at the coupling rod, umbo, incus, and footplate. The TBs were subsequently defrosted. The MET was implanted and coupled to the ossicular chain. Different coupling loads were measured at the incus, the umbo, and the footplate.

RESULTS

Optimal transfer function between the MET transducer and the oval window was achieved during contact when the coupling rod advanced 0.0625 mm (90 degrees rotation). Additional advances of 0.0625 mm (180 degrees turn = 0.125 mm) resulted in a decreased vibrational amplitude, ranging between 20 and 40 dB below 3 kHz. The lowest linear distortion occurred up to 10 kHz during direct contact without advancing the coupling rod.

Experience with the SOUNDTEC implantable hearing aid

OBJECTIVE

To assess the efficacy, morbidity, and patient satisfaction of the SOUNDTEC semi-implantable hearing aid.

STUDY DESIGN

Retrospective case review.

SETTING

Two tertiary referral centers (the Silverstein Institute and the Atkins Institute).

PATIENTS

Sixty-four (four bilateral placements) patients with bilateral moderately severe sensorineural hearing loss: 47 patients had previously worn hearing aids.

INTERVENTIONS

After separating the incudostapedial joint, a magnet encased in a titanium canister with a ring was introduced onto the stapes neck. Gelfoam or adipose tissue was used to stabilize the magnet. After 3 months, the external processor was fitted.

MAIN OUTCOME MEASURES

At 1 month, audiometric testing was performed and functional gain was assessed. Patient acceptance and implant performance were measured by a visual analogue questionnaire.

RESULTS

The device produced an average functional gain of 26 dB. Fifty-five percent of patients complained of magnet movement; this was eliminated in 80% of Silverstein Institute patients when the external processor was worn and fat was used to stabilize the magnet.

CONCLUSION

The SOUNDTEC direct device is well tolerated in the majority of patients, with a significant increase in functional gain. Magnet instability and noise were the most frequent complaints and improved with processor placement and anchoring the magnet with fat. This electromagnetic semi-implantable hearing aid confers greater functional gain over conventional hearing aids and reduces occlusion effect and feedback.

Phase 1 clinical trial results of the Envoy System: a totally implantable middle ear device for sensorineural hearing loss

OBJECTIVES

This report will present the results of the USA Phase 1 clinical trials for the Envoy System (St. Croix Medical): A totally implantable middle ear hearing system for sensorineural loss.

STUDY DESIGN

A prospective, single-subject, repeated-measures, multicenter study was performed to evaluate safety and functionality of the Envoy System. Data collected included Abbreviated Profile of Hearing Aid Benefit, bone conduction threshold, speech reception threshold, functional gain, word recognition, and adverse events. Testing was performed unaided, with the patient's best-fit hearing aid, and post device activation at 2 (trial endpoint) and 4 months.

RESULTS

Five of 7 patients at the 2-month postactivation period had working systems. All 5 patients perceived benefit increases with the Envoy System over their best-fit hearing aid, including communication in high background noise levels. Word recognition was improved over hearing aids. Functional gain and speech reception thresholds were similar for the Envoy device and hearing aids.

CONCLUSIONS

The feasibility trial has shown the Envoy device, a totally implantable middle ear device, can safely sense and drive the ossicular chain.

EBM RATING

B-2.

Comparison of the implantability of electronic hearing devices in a virtual reality planning environment and in human temporal bones

OBJECTIVE

To develop a procedure using a virtual reality (VR) environment that permitted us to simulate the preoperative fitting of an electronic implantable hearing device (IHD) and assess its implantability.

MATERIAL AND METHODS

This was an experimental, prospective study based on VR simulations involving the pre- and postoperative comparison of the implantability of an IHD. The preoperative possibility of implanting an IHD in a VR environment was compared with the postoperative implantability of the device in the temporal bones of human cadavers and patients. Study groups were analyzed according to the criteria "VR implantation" and "real surgery" using contingency tables.

RESULTS

A computer simulation method based on CT images was developed for the preoperative planning of the implantation. The VR simulation proved feasible in all cases (15 temporal bones and 24 patients). There was no significant difference between the process of implanting the IHD in patients or in the VR environment. These results indicate that VR-based test fittings of an IHD allow prediction of the implantability of an IHD prior to actual surgery.

CONCLUSION

We have described the development of a novel VR procedure for predicting the implantability of hearing devices in otoneurosurgical applications. The VR procedure can be applied universally and may also be used for other parts of the body.

Biomechanical influences of magnetic resonance imaging on the SOUNDTEC Direct System implant

OBJECTIVE

The purpose of this study was to measure the forces experienced by the SOUNDTEC Direct System magnetic implant during 0.3-T MRI.

STUDY DESIGN

Torsional and linear forces imposed on 8 implants were measured by using calibrated neurologic Von Frey hairs and were compared with finite-element analysis predictions and the forces required to separate the incudostapedial joints of unpreserved temporal bones. An implanted embalmed autopsy specimen was also examined before and after 1.5-T MRI.

RESULTS

Peak linear force at the orifice of the MRI core measured 0.51g (+/-0.2 SD). Maximum torque occurred at the MRI core center and measured 11.4g-cm (+/-1.2 SD). The mean torque required to separate the incudostapedial joints of 12 unpreserved temporal bones was 33.8g-cm (+/-20.4 SD). The autopsy specimen sustained a 1.5-T MRI scan without disruption of the ossicular chain or explantation.

CONCLUSIONS

Physical and mechanical testing of the SOUNDTEC implant indicates that the structural integrity of the ossicles will be maintained during 0.3-T MRI of the human head.

Middle ear electromagnetic semi-implantable hearing device: results of the phase II SOUNDTEC direct system clinical trial

OBJECTIVE

To assess the safety and efficacy of the SOUNDTEC Direct System, a partially implantable electromagnetic middle ear hearing device.

STUDY DESIGN

Food and Drug Administration Phase II clinical trial of 103 patients at 10 sites across the United States.

SETTING

Tertiary referral medical centers.

PATIENTS

Individuals with bilateral moderate to moderately severe sensorineural hearing impairment who had worn optimally fit hearing aids for at least 45 days.

INTERVENTIONS

Therapeutic intervention included implantation of a 27-mg neodymium iron boron magnet encased in a laser-welded titanium canister onto the incudostapedial joint, followed, after a 10-week healing period, by fitting with a deep earmold coil assembly and activation of the sound processor.

MAIN OUTCOME MEASURES

Functional gain, speech recognition in quiet and noise, articulation index scores, perceived aided benefit, sound quality judgments, satisfaction, and presence of feedback and occlusion with the Direct System were compared with those of the patients' optimally fit hearing aid.

RESULTS

The results of this multicenter clinical trial were submitted to the Food and Drug Administration on April 13, 2001, and are presented here. The results with the use of the SOUNDTEC Direct System compared with an optimally fit hearing aid provided an average 7.9-dB increase in functional gain in the speech frequencies (500-4,000 Hz) and a 9.6 dB gain in high frequencies (2,000, 3,000, and 4,000 Hz). There was a statistically significant average increase of 5.3% in speech discrimination. The mean speech perception in noise test score was improved, but the improvement was not statistically significant. Subjective tests using abbreviated profile of hearing aid benefit and the Hough Ear Institute Profile demonstrated scores statistically improved over the hearing aid condition. These subjective tests measured areas such as the presence of occlusion and feedback, speech quality judgments, device preference, and perceived aided benefit.

CONCLUSIONS

The results of this Phase II clinical trial demonstrate that the SOUNDTEC Direct System provided statistically significant reduction in feedback and occlusive effect as well as a statistically significant improvement in all the following categories: functional gain, articulation index scores, speech discrimination in quiet, perceived aided benefit, patient satisfaction and device preference over the patient's optimally fit hearing aid.

Long-term results and experience with the first-generation semi-implantable electromagnetic hearing aid with ossicular replacement device for mixed hearing loss

OBJECTIVE

To document the long-term surgical and audiologic results of the implantation of a first-generation semi-implantable hearing aid for mixed hearing loss, consisting of a magnetic partial or total ossicular replacement prosthesis and an electromagnetic driver fitted in the ear canal. The short-term results have previously been published as excellent in both surgical and audiologic terms. To analyze and discuss reasons of treatment failure, as well as future perspectives.

STUDY DESIGN

Patient file review, follow-up otomicroscopic examination and audiometry, as well as patient interview. SETTING Tertiary referral center at a University hospital.

PATIENTS

Of nine patients operated on, six with a mixed hearing loss after chronic otitis media could be evaluated primarily. Two underwent implantation with a partial and four with a total ossicular replacement prosthesis.

MAIN OUTCOME MEASURES

Use of and satisfaction with the hearing aid, apparatus function and integrity, hearing without electromagnetic driver, prostheses containment, drum abnormalities, nonaudiologic ear symptoms, e.g., discharge.

RESULTS

All patients attended follow-up for a mean of 9.5 years after implantation (range 8.8-10 years). No patients used the semi-implantable hearing aid at follow-up. The mean semi-implantable hearing aid using time was 24 months (range 3-60 months). The main reasons for discontinuation of use were problems fitting the electromagnetic driver correctly in the ear canal and prosthesis extrusion or dislocation.

CONCLUSIONS

Despite excellent short-term surgical and audiologic results, it is concluded that these first long-term results of the first-generation electromagnetic semi-implantable hearing aids with ossicular replacement prosthesis for mixed hearing loss are disappointing. However, improvements in the surgical approach and in the reshaping, refinement, and overall improvement of the semi-implantable hearing aid could lead to satisfactory treatment of this group of patients.