Electrically Evoked Auditory Brain Stem Responses for Lateral and Medial Placement of the Clarion HiFocus Electrode

In Brief Objective The purpose of this study was to compare the electrically evoked auditory brain stem response (EABR) for lateral and medial placement of the Clarion HiFocus cochlear implant electrode array via the electrode positioning system (EPS). Design Twenty-five adult and pediatric cochlear implant recipients participated in the study. Intraoperatively recorded EABRs were evoked by stimuli via three intracochlear electrodes representing apical, medial, and basal locations, and responses were elicited before and after positioner insertion. Evoked potential measures of wave V amplitude and threshold were examined for statistical significance using ANOVA for repeated measures and Chi-Square methods. Results For a given supra-threshold stimulus level, the increase in EABR wave V amplitude was significantly larger after EPS placement compared to before EPS placement for electrodes 1 (apical) and 13 (basal). Likewise, when the stimulus was decreased to obtain a minimal amplitude, the wave V threshold was significantly lower after EPS placement for electrodes 7 (medial) and 13. The number of measurements that showed decreased wave V threshold after EPS insertion was significantly dependent on intracochlear electrode location. Conclusions Placement of the Clarion Electrode Positioning System following HiFocus electrode insertion resulted in a reduction in the electrical current required to activate the auditory system. The effect of the EPS was greatest for the basal location, demonstrated by lower wave V thresholds and a larger percentage increase in wave V amplitude. The EABR reflected electrophysiologic changes relative to lateral-to-medial changes in intracochlear electrode position due to the EPS. In the past few years there has been a great deal of interest in new cochlear implant designs that make intracochlear electrodes lie closer to the medial wall, and therefore closer to the neurons that are electrically stimulated by the implant. Animal research and cochlear modeling have suggested that with this kind of “perimodiolar” placement electrophysiologic thresholds are reduced and electrical dynamic range may be increased. The current study extends these earlier results to human patients by measuring electrically evoked auditory brain stem responses (EABR) intraoperatively before and after placement of the Clarion electrode positioning system (EPS), a device intended design to improve perimodiolar placement. Results from this study indicate that the effect of the EPS was greatest for the basal location, demonstrated by lower wave V thresholds and a larger percentage increase in wave V amplitude. The EABR reflected electrophysiologic changes relative to lateral-to-medial changes in intracochlear electrode position due to the EPS.