Electric Acoustic Stimulation and Hearing Preservation : Atraumatic Surgical Techniques and Outcome

Dr Zeeshan AhmadM.S.(ENT,PGY1)

Department of ENT,NMCH,Patna.

18-10-2012

Cochlear Implant History#Pre-1960’s

- beginning studies of electrical stimulation on humans

#1960’s- active research

of electrical stimulation in human ears

#1970’s- first wearable

implants designed for long-term stimulation

#1980’s- commercial

development of the cochlear implant device

began

…continued #1985- United States Food &

Drug Administration (FDA) granted the

first approval for implantation in adults

#1990- FDA granted approval

for cochlear implants in children

#1999 - Electric Acoustic stimulation first described by C. Von Ilberg & J Kiefer of Frankfurt

University. Same year first EAS implant was done.

Something beyond

“JUST COCHLEAR

IMPLANT”

From CI to EAS : Basis

Feasibility to preserve preoperative low frequency hearing when performing CI in the Scala Tympani(ST) gave rise to the concept of ELECTRIC ACOUSTIC STIMULATION.

An EAS System (External components)

A cochlear implant converts everyday sounds into coded electrical pulses. These pulses stimulate the auditory nerve. The brain interprets these signals as sound.

Mid and high frequency sounds are picked up by the microphone of theDUET 2 Audio Processor and are converted into a special code.

 

ELECTRIC STIMULATION:

ELECTRIC STIMULATION:

This code is sent to the coil and is transmitted across the skin.

The implant interprets the code and sends electrical pulses to the electrodes in the cochlea.

The auditory nerve relays these signals to the brain

ACOUSTIC STIMULATION:Acoustic amplification turns up

the volume on the sounds that the cochlea is still able to hear. For EAS, only the low frequencies are amplified.

Low frequency sounds are picked up by the microphone and are digitally processed.

Sounds are amplified by the loudspeaker located in the ear hook and are relayed via the ear mould to the ear canal.

ACOUSTIC STIMULATION:

Sounds reach the undamaged areas of the cochlea responsible for processing low-frequency sound.

The auditory nerve sends the signals to the brain.

The importance of high frequency hearing

Our brain relies extensively on high frequency sounds to clearly decipher and understand spoken words, especially at a distance or in noisy places.

High frequencies deliver the additional vital details of sound – making the sounds you hear richer, fuller and crisper in every way.

Hearing high frequency sounds clearly can enrich your awareness and enhance your experience.

High frequency hearing loss

Did you know that many words begin and end with high frequency sounds?

That explains why, when you lose high frequency hearing, words seem to merge together and become indistinguishable from one to the next.

In addition to human speech, your environment is full of many other high frequency sounds, without which you can’t get a complete sense of a situation.

Let’s see a typical audiogram for an individual with high frequency hearing loss.

The red line shows a person's hearing profile - how much sound they can hear at different frequencies.

The closer the line is to the bottom of the audiogram, the greater the hearing loss.

Someone with severe to profound high frequency hearing loss would struggle to hear the sounds above the red line (speech, birdsong, music, telephone ringing etc).

Indications and Criteria for EAS(a)Audiological criteria

◦below 1.5 kHz – No or moderate HL◦above 1.5 kHz – Severe to profound

SNHL

Indications and Criteria for EAS(b)Speech recognition• The patient's monosyllable word score

should be ≤ 60% at 65dB SPL in the best aided condition.

Indications and Criteria for EAS(c)Additional criteria No progressive hearing loss(10/2,

15/1 in 1yr)

No autoimmune inner-ear disease No hearing loss as a result of

meningitis, otosclerosis or ossification

No malformation or obstruction of the cochlea

Maximum air–bone gap 15dB HL No external ear contraindications

to using amplification devices.

SURGERY :-The EAS surgeries are aimed at preserving the anatomical structures and preserving the cochlear function. Steps are as follows:-Pre-incision measures

◦Antibiotic prophylaxis◦Systemic corticosteroids

Posterior tympanotomy◦A standard mastoidectomy is done◦Anatomy identified◦All bone dust particles removed

SURGERY :-Endosteum or Round Window

exposure at the Cochleostomy site◦Currently, RW approach is mostly

usedTopical steroid application

◦Dexamethasone 1mg/ml or Triamcinolone 40 mg/ml

◦Allowed for minimum 30 minutes

SURGERY :-Placing the Implant

◦Subperiosteal pocket created◦Well for Implant created◦Bone dust and blood removed◦New gloves◦Subcutaneous fat autografts taken◦Implant inserted into the implant well◦Electrode array is coated with

Hyaluronic acid and Steroid

SURGERY :-Inserting the Electrode Array

◦Electrode tip is placed in the opening(RW or Cochleostomy) and introduced into the Scala Tympani supero-posterior to antero-inferior

◦Slowly to prevent intracochlear pressure build-up

◦Inserion is stopped when predefined length is reached or resistance is felt

◦ tip touching the ST Modiolar wall avoided

◦Opening closed with previously taken antibiotic soaked Fat Autografts.

SURGERY :-Securing the Electrode and

Closing the Retroauricular Incision in Three Layers◦Care is taken that Ossicular Chain is

not touching with any component

Electrode design for HPFor hearing preservation the

Electrodes are designed to create least trauma to intracochlear structures ◦Thinner caliber 0.25mm at tip and

0.8mm at entry site◦More flexible Tip regions◦Tailoring the insertion depth

Outcome of EAS

HEARING PRESERVATION◦The success of EAS Implant depends

upon the RLFH(Residual Low Frequency Hearing).

◦The cochlear hybrid implant using 6mm and 10mm elctrodes resulted in long term hearing preservation in 75% of subjects.

◦Studies using Med-El elctrodes showed a successful HP in 12/18 subjects with complete hearing loss in 3/18 subjects.

Outcome of EAS

SPEECH PERCEPTION with EAS◦EAS significantly improves speech

perception in quiet and in noise compared to acoustic hearing only.

◦In a study by Gstoettner et al EAS treatment yielded an improvement in speech perception in quiet from 24% preoperatively to 71% after 12 months.

Outcome of EAS

Music appreciation and Subjective benefit with EAS◦EAS users perform better on melody

and instrument recognition than CI users.

◦Subjective benefit of EAS was assessed with APHAB(Abbreviated Profile of Hearing Aid Benefit).

◦Observed with EAS fitting and improved gradually with experience.

THANKYOU

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