The Envoy Esteem Implantable Hearing System




This article discusses the Envoy Esteem implantable hearing system, a completely implantable hearing device. The device is indicated for patients older than 18 years with stable moderate to severe sensorineural hearing loss and good speech discrimination. The device is placed through an intact canal wall tympanomastoidectomy with a wide facial recess approach. The implant is typically activated at 6 to 8 weeks postoperatively and usually requires several adjustments for optimal performance. The sound processor/battery lasts 4.5 to 9.0 years and can be replaced through a minor outpatient procedure.


Key points








  • The Envoy Esteem is the first completely implantable hearing device.



  • The Envoy Esteem is indicated for patients older than 18 years of age with stable moderate to severe sensorineural hearing loss and word discrimination scores greater than 40%.



  • Patients undergoing implantation should have limited hearing benefit with best-fit hearing aids.



  • The surgical procedure is technically demanding, and the best hearing results are typically seen at 6 months postoperatively.



  • Complications with the Envoy Esteem are uncommon, and hearing is generally better than with hearing aids.




Videos of diode laser using to section incus long process, laser char removal from incus long process, completion of incus sectioning, cleaning of methylene blue from stapes capitulum, application of precoat to stapes capitulum, and application of cement around sensor and drive bodies accompany this article at http://www.oto.theclinics.com/




Introduction


Hearing loss is the number one sensory impairment and is a growing epidemic in the United States. Hearing loss is generally classified as conductive, sensorineural, or mixed. Of these, sensorineural hearing loss is the most common. Approximately 11.3% of the United States population or 34.25 million people have hearing loss. According to the National Institute on Deafness and Other Communication Disorders, approximately 17% of American adults report some degree of hearing loss. It increases in all populations with age and is showing an alarming increase in adolescents.


Approximately 8.5 million people wear hearing aids, but only 20% to 25% of individuals who could benefit from hearing aids actually wear them, for several reasons. Financial considerations are undoubtedly important; hearing aids typically cost $1000 to $3000 each, with most patients requiring 2, and need to be replaced/upgraded on average every 5 years. Some patients do not like the appearance of hearing aids. Other people do not believe they have a hearing handicap, and some think their family members are pressuring them to obtain hearing aids.


Although many patients with hearing aids are satisfied with them, some complain of ear canal irritation, ear canal infections, feedback, and an occlusion effect. Hearing aids can break or can be lost. Most patients remove their hearing aids when they go to bed, thus requiring other assistive devices to hear appliances such as alarms and the phone. Furthermore, hearing aid batteries need to be replaced weekly, and the aids themselves have a limited lifespan of approximately 5 years before they need to be replaced.


Patients with mild to moderate hearing losses and good word discrimination, in general, do best with hearing aids. Patients with severe and profound hearing losses with poor word discrimination are better served with cochlear implants. Patients in the middle of these 2 groups (moderate to severe sensorineural hearing loss with word recognition scores greater than 40% while wearing hearing aids) are candidates for active middle ear implants, such as the Envoy Esteem.




Introduction


Hearing loss is the number one sensory impairment and is a growing epidemic in the United States. Hearing loss is generally classified as conductive, sensorineural, or mixed. Of these, sensorineural hearing loss is the most common. Approximately 11.3% of the United States population or 34.25 million people have hearing loss. According to the National Institute on Deafness and Other Communication Disorders, approximately 17% of American adults report some degree of hearing loss. It increases in all populations with age and is showing an alarming increase in adolescents.


Approximately 8.5 million people wear hearing aids, but only 20% to 25% of individuals who could benefit from hearing aids actually wear them, for several reasons. Financial considerations are undoubtedly important; hearing aids typically cost $1000 to $3000 each, with most patients requiring 2, and need to be replaced/upgraded on average every 5 years. Some patients do not like the appearance of hearing aids. Other people do not believe they have a hearing handicap, and some think their family members are pressuring them to obtain hearing aids.


Although many patients with hearing aids are satisfied with them, some complain of ear canal irritation, ear canal infections, feedback, and an occlusion effect. Hearing aids can break or can be lost. Most patients remove their hearing aids when they go to bed, thus requiring other assistive devices to hear appliances such as alarms and the phone. Furthermore, hearing aid batteries need to be replaced weekly, and the aids themselves have a limited lifespan of approximately 5 years before they need to be replaced.


Patients with mild to moderate hearing losses and good word discrimination, in general, do best with hearing aids. Patients with severe and profound hearing losses with poor word discrimination are better served with cochlear implants. Patients in the middle of these 2 groups (moderate to severe sensorineural hearing loss with word recognition scores greater than 40% while wearing hearing aids) are candidates for active middle ear implants, such as the Envoy Esteem.




Device description


The Envoy Esteem implantable hearing system is composed of a sound processor/battery, sensor, and driver. The sensor and driver are placed in the mastoid cavity ( Fig. 1 ), whereas the sound processor/battery is placed in a subcutaneous pocket posterior to the mastoid cavity. The sensor is attached to the incus body. Movements of the tympanic membrane are transmitted to the malleus and incus. Through sensing vibrations of the incus, the sensor basically acts as an internal microphone. It sends electrical information via insulated wires to the replaceable/programmable sound processor/battery. From here, information is related to the driver, which is a piezoelectric transducer attached to the stapes head. The stapes is then mechanically moved, which stimulates the cochlea. Through driving the ossicular chain directly, this middle ear implant can bypass some of the problems of conventional hearing aids.




Fig. 1


Right mastoid cavity, with sensor seen on the left and driver seen on the right.




Candidacy for surgery


Patients who are candidates for the Envoy Esteem should be older than 18 years and have a stable moderate to severe sensorineural hearing loss with word recognition scores greater than 40%. Ideal candidates are those who have tried properly fitted hearing aids for at least 6 months. Because few if any insurance companies cover the procedure (which can range from $35,000–$45,000 per ear), patients should have sufficient finances so that the procedure would not cause excessive financial strain. Patients should also be in adequate health and be able to tolerate a general anesthetic.


Contraindications to surgery include a history of active chronic otitis media, cholesteatoma, otosclerosis, retrocochlear disease, inner ear malformations, documented fluctuating hearing loss, Meniere disease, otitis externa, disabling tinnitus, conductive or mixed hearing loss, and previous ossiculoplasty or stapes surgery. Patients who have undergone prior tympanostomy with pressure equalization tube placement and/or tympanoplasty might be candidates provided they do not have any residual conductive hearing loss. Other contraindications are the need for periodic MRI, because the device is not MRI-compatible; the presence of wound healing issues; and a history of prior radiotherapy to the ear and temporal bone.




Preoperative planning and preparation


An important aspect in counseling patients about the Envoy Esteem is ensuring that patients have realistic expectations about the device. Not all patients will have the same or an ideal result with the device. The device may not overcome all of the limitations of their hearing aids, and the hearing may not be significantly better than that experienced with a pair of well-fit hearing aids. Furthermore, in many patients, the hearing slowly improves over several months after surgery, and several fittings/adjustments are necessary. For most patients, 2 to 3 device adjustments within the first 6 months are necessary. Revision surgery and/or explantation also may be necessary if the device is not functioning adequately or if surgical complications occur. Lastly, the patient will still likely require a hearing aid in the contralateral ear.


A 2004 phase I clinical trial reported on 57 patients with adverse events, including taste disturbance (40%), ear effusion (30%), and tinnitus (14%), and 3 patients (5%) required surgical revision. Therefore, informed consent requires discussing potential intraoperative and postoperative complications, including the possibility of aborted surgery because of inadequate ossicular chain mobility, or inadequate space in the mastoid cavity. Other potential complications include bleeding, infection, tympanic membrane perforation, facial paresis or paralysis, deafness, vertigo, new or worsened tinnitus, injury to the ear canal, injury to the labyrinth, injury to the sigmoid sinus, and injury to the dura resulting in a cerebrospinal fluid leakage. Most patients will have a temporary ipsilateral taste disturbance because of sacrifice of the chorda tympani nerve, which is required in almost all cases.


Late complications can occur, and these most commonly include limited gain, feedback, scar tissue formation, worsened hearing, infection, biofilm formation, device exposure, and device extrusion. Revision surgery and/or device explantation may be necessary in selected cases. Although reconstruction of the ossicular chain can occur during explantation, the hearing results may not be the same as at baseline before implantation.


If a patient is deemed to be a good candidate for surgery and is interested in proceeding, a computed tomography (CT) scan of the temporal bones without contrast is obtained to ascertain if enough space is available for the sensor and driver. The distance between the stapes head and sigmoid sinus should be more than 22.0 mm, and the distance between the incus body and middle cranial fossa dural plate should be more than 2.5 mm. In patients with symmetric hearing between each ear, the larger mastoid is generally selected as the best ear to implant first.




Surgical technique


Patient Positioning


The patient is brought to the operating room and is placed on a padded operating table in the supine position. General anesthesia is administered via laryngotracheal intubation. A laryngeal mask airway is not recommended, because the total surgical time is approximately 3.5 hours. A short-acting paralytic anesthetic is administered, because facial nerve monitoring is used during the procedure. The table is turned 180°. The head is placed on a foam headrest and rotated away so that the operative ear is facing upward and taped in place. The facial nerve monitor electrodes are placed in the orbicularis oris and orbicularis oculi muscles and the monitor is tested to ensure it is working correctly.


Procedural Approach


The ideal sound processor location is marked on a flat part of the skull posterior to the anticipated mastoidectomy. An S-shaped incision is marked on the skin above and anterior to the anticipated sound processor position, curving toward the mastoid tip ( Fig. 2 ). A small hair shave around the incision is performed. Plastic drapes are placed to protect the hair from blood and debris. Local anesthetic is infiltrated into the intended incision for hemostasis.


Apr 1, 2017 | Posted by in OTOLARYNGOLOGY | Comments Off on The Envoy Esteem Implantable Hearing System

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