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Electrode Arrays

 

Advances and Innovations
in Cochlear Implant Electrodes

Highly adaptable electrode designs
for every anatomical circumstance

Contra-indications for the electrical stimulation of human auditory nerve fibres are rapidly becoming limited. This is due to the immense success of the cochlear implant in restoring speech comprehension in anatomy that has not changed over time. Key to the growing success of the implant is the evolution of the electrode interface. Such interfaces must be adaptable to the unusual anatomical circumstances that often characterise deafness.

For more than two decades MED-EL has provided patients with a variety of electrodes specific to patient condition. With an electrode extent of 27 mm, the Standard Intra-cochlear Multichannel Electrode Array is a 12 channel device designed to stimulate the spiral ganglion from the base to the apex (Complete Cochlear Coverage). The 2.4 mm contact separation favours minimum channel interaction in monopolar mode. The soft silicone array preserves the basilar membrane and the organ of Corti during the insertion process. Complete Cochlear Coverage electrodes with deep insertion properties are made possible by the unique wave-shape of the wires. The wave-shaped (sinus) wires make the electrode extremely flexible and atraumatic. Atraumaticity of the electrodes is further enhanced by its lateral wall placement, as this does not apply any forces against the modiolus. Lateral wall electrodes can be inserted through the round window membrane in most cases. Round window insertion has become the favoured path of cochlear access to minimise trauma and ensure entrance into the scala tympani.

A second variant of the electrode, called Medium Electrode Array, has a contact separation of 1.9 mm, and electrode extent of 21 mm. It is designed for hearing preservation or for shorter scala tympani length. Another variation is the short array which is designed with 1.1 mm contact separation and 13 mm electrode extent. This array is designed specifically for patients with an ossification or an obstruction at around 15 mm into the scala or for patients with severe incomplete partition. In the case of a seriously ossified cochlea, a Split Electrode Array allows the introduction of 2 branches into the first turn of the scala through a superior and an inferior cochleostomy both located in the basal turn. Finally, a special custom-made device for the common cavity cases is available, to allow the electrode array to be optimally placed in a malformed cochlea.

For patients with retrocochlear pathology, there is the option of an Auditory Brainstem Implant (ABI). The ABI restores hearing sensation by direct stimulation of neural tissue at the surface of the cochlear nucleus. 

Special arrays, such as the FLEXEAS, are available for Electric Acoustic Stimulation (EAS). This electrode has a length of 24 mm with a contact spacing of 1.9 mm. These arrays are minimally invasive and maximally atraumatic in order to preserve the residual hearing of the patient (i.e to preserve the remaining hair cells in the basilar membrane region). Combined electrical and acoustic stimulation is the optimal solution for patients who have a relatively good low frequency residual hearing and a severe to profound sensorineural hearing loss in the high frequencies. These patients often wear a hearing aid. The hearing aid is, however, of little help in conveying auditory signals to the high frequency region which is critical for understanding speech. It has been demonstrated that electrical stimulation in this high frequency region can improve the quality of the sound perceived by the patient. The acoustic and the electrical information conveyed to the brain are additive and non-interfering.

Electrodes with a provision for pharmacotherapy are also being developed. These arrays could deliver nerve growth factors or steroids as well as stimulating the nerve fibres. Results show that for maximum output (effective stimulation on all channels, minimum trauma, adaptability) the electrode should be small in size, should not be pre-shaped, and should have a limited number of contacts distributed over a large extent.

MED-EL electrodes are minimally invasive and are designed to preserve the internal tissues of the cochlea. These arrays are especially soft and flexible for optimal insertion.

Optimum insertion characteristics include:

  • Insertion ease
  • Insertion depth
  • Minimal insertion trauma

 

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