Electrode Placement and Audiologic Outcomes With the Advanced Bionics HiFocus L23 Electrode

Cochlear implants (CI) are biomechanical sense prostheses approved by the FDA for the treatment of sensorineural hearing loss. CI's function by bypassing the absent or dysfunctional cochlear end organs to directly electrically stimulate the spiral ganglion and cochlear nerve. A variety of commercially available FDA-approved implants exist for the treatment of severe to profound deafness. Implants are typically designed in two broad categories: lateral wall electrodes and perimodiolar. Perimodiolar electrodes are precurved electrodes that are designed to hug the center of the cochlea (modiolus) after insertion. Lateral wall electrodes are slim and straight, hugging the lateral wall on insertion. Recent studies have shown that electrode design and location within the cochlea impact patient performance. Specifically, electrodes located completely within the scala tympani are associated with better outcomes than those that cross over from the scala tympani to the scala vestibuli during insertion. The same study has shown that lateral wall electrodes are less likely than perimodiolar electrodes to have scalar excursion to the scala vestibuli. Location matters with these implants because electrode position completely within the scala tympani is associated with higher rates of preservation of residual hearing. Minimizing cochlear trauma allows for preservation of residual acoustic hearing particularly in low frequencies. While this low frequency hearing is of little benefit independently, when combined with the electrical stimulation from the cochlear implant patients have improved performance. The HiFocus L23 electrode is manufactured by Advanced Bionics (Valencia, California), and is FDA approved for the treatment of sensorineural hearing loss in adult and pediatric patients. It is designed as a slim and straight lateral wall electrode that can be inserted with low force to minimize intracochlear trauma. While pre-market studies were performed by Advanced Bionics as a part of its approval for use by the FDA, no post-market studies have been performed to assess the audiologic outcomes, electrode location after insertion, and hearing preservation rates when using this electrode. These aims will be accomplished through several means. Audiologic speech performance will be assessed through a standardized clinical/audiometric protocol currently followed by the Vanderbilt University Medical Center cochlear implant team. Electrode location for all participants will be determined using novel software created by Vanderbilt engineering faculty and graduate students that uses computerized tomography (CT) images obtained as a part of practice postoperatively or intraoperatively using an FDA approved Xoran xCAT® device, a portable flat panel volume computerized tomography (fpVCT) machine (Vanderbilt) or regular CT scan at participating institutions as applicable. These images can be registered to existing pre-operative conventional CT scans and used to produce 3-dimensional models of electrode placement within each patient's cochlea. This software is investigational and used in other research studies for the same purpose. The extent to which the electrode remains in the desired location (scala tympani) will then be correlated with audiologic outcomes as obtained above. Residual hearing rates and quality of life measures will be obtained as a part of audiologic testing. If a fine resolution, high quality conventional head CT has been previously obtained, or is obtained as part of routine care this scan may be used in place of the fpVCT or in addition to the fpVCT scan. The option of having a conventional head CT performed in radiology for research purposes in place of the fpVCT head CT scan will also be available. Surgeons will complete surveys after each case concludes to evaluate the ease of insertion and will record the insertion via standard recording techniques in the operating room that are available for any microscopic case. These videos for all surgeries will be blinded and reviewed at Vanderbilt for ease and speed of insertion.