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Intraoperative Electrically Evoked Compound Action Potential (ECAP) Measurements in Traditional and Hearing Preservation Cochlear Implantation

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Background: In current practice, the status of residual low-frequency acoustic hearing in hearing preservation cochlear implantation (CI) is unknown until activation two to three weeks postoperatively. The intraoperatively measured electrically evoked compound action potential (ECAP), a synchronous response from electrically stimulated auditory nerve fibers, is one of the first markers of auditory nerve function after cochlear implant surgery and such may provide information regarding the status of residual low-frequency acoustic hearing.
Purpose: This study aimed to evaluate the relationship between intraoperative ECAP at the time of CI and presence of preoperative and postoperative low-frequency acoustic hearing.
Research Design: A retrospective case review.
Study Sample: Two hundred seventeen adult ears receiving CI (42 Advanced Bionics, 82 Cochlear, and 93 MED-EL implants).
Interventions: Intraoperative ECAP and CI.
Data Collection and Analysis: ECAP measurements were obtained intraoperatively, whereas residual hearing data were obtained from postoperative CI activation audiogram. A linear mixed model test revealed no interaction effects for the following variables: manufacturer, electrode location (basal, middle, and apical), preoperative low-frequency pure-tone average (LFPTA), and postoperative LFPTA. The postoperative residual low-frequency hearing status was defined as preservation of unaided air conduction thresholds ≤90 dB at 250 Hz. Electrode location and hearing preservation data were analyzed individually for both the ECAP threshold and ECAP maximum amplitude using multiple t-tests, without assuming a consistent standard deviation between the groups, and with alpha correction.
Results: The maximum amplitude, in microvolts, was significantly higher throughout apical and middle regions of the cochlea in patients who had preserved low-frequency acoustic hearing as compared with those who did not have preserved hearing (p = 0.0001 and p = 0.0088, respectively). ECAP threshold, in microamperes, was significantly lower throughout the apical region of the cochlea in patients with preserved low-frequency acoustic hearing as compared with those without preserved hearing (p = 0.0099). Basal electrode maximum amplitudes and middle and basal electrode thresholds were not significantly correlated with postoperative low-frequency hearing.
Conclusions: Apical and middle electrode maximum amplitudes and apical electrode thresholds detected through intraoperative ECAP measurements are significantly correlated with preservation of low-frequency acoustic hearing. This association may represent a potential immediate feedback mechanism for postoperative outcomes that can be applied to all CIs.
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Keywords: cochlear implantation; electrically evoked compound action potential; hearing preservation; maximum amplitude; residual hearing; threshold

Affiliations: Vanderbilt University Medical Center, Nashville, TN

Appeared or available online: July 2, 2019

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