p2g1

Implantable Hearing Aids

Dr. George Gates presented the first half of the Plenary Session on "Research Advances in Hearing Health". He began by noting that there are two types of research: basic or fundamental research, which is done in the lab, and clinical research, which involves real doctors and real patients. His presentation covered two topics within the field of clinical research: implantable hearing aids and a new treatment for Meniere's Disease.

Dr. Gates began his discussion of implantable hearing by noting several advantages compared to conventional hearing aids:
- Freedom from ear canal occlusion
- Freedom from hearing aid whistling
- Better high frequency response
- Better high frequency fidelity
- Potential for higher hearing aid gain
- Better hearing in noise

The disadvantages of implantable hearing aids include:
- Higher cost - between $5000 and $20,000 per ear
- It's a surgical procedure
- Advances in conventional aids have reduced the comparative advantages of implantable aids

There are currently three types of implantable hearing aids: transcanal or direct, transcutaneous, and totally implantable

An example of the direct system is the SoundTec, which includes a magnet implanted under the stapes; the magnet is driven by a coil in the ear. This involves an outpatient procedure that lasts 15 to 30 minutes. It is FDA approved and costs about $5000. The external components of the study models are behind-the-ear (BTE), but an in-the-ear (ITE) model is coming out. The SoundTec is recommended for moderate hearing loss; it provides about five or ten db better response throughout the spectrum, compared to conventional aids. The surgical procedure has minimal effect on unaided hearing. People prefer the sound quality over that provided by conventional aids. It is crucial that the coil be fitted properly, and that can be a tedious procedure.

The second type of implantable aid is the transcutaneous, of which the Soundbridge is an example. The microphone and amplifier sit outside the temple, and the magnet is attached to the second hearing bone.

One version of the totally implantable hearing aid is the St. Croix system. It uses the eardrum as the microphone, which eliminates the need for external parts. An attached coil drives a second coil deeper in the ear. This aid requires more complex surgery; also, a new battery is required every five years, which requires an additional surgery.

The final example is the TICA fully implantable system from Implex. The microphone fits under the skin of the ear canal, which allows this system to take advantage of the ear's acoustics. The microphone drives amplification electronics, which then drive the hearing bones directly. This system requires the removal of the head of the malleus, so it's unlikely that the FDA would ever approve it. The TICA system includes a rechargeable battery.

In summary, the cost of the implantable systems is high; the benefit is real, but small. As with a CI, MRI-compatibility may be a problem. These devices may best be used by people who can't use a conventional hearing aid.

Q: There's something called the Bone Anchored Hearing Aid (BAHA) that some people think will replace the CI. Do you know anything about that?
A: It's a Swedish device that's for people who have irreversible conduction problems. The cochlea must be in pretty good shape. It won't replace the CI; it really serves a very different purpose.

Q: Are implantable hearing aids useful for people who have otosclerosis and have had stapes surgery?
A: No, but the BAHA would help.