Abstract
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.
Key Words
cochlear implantation - electrically evoked compound action potential - hearing preservation
- maximum amplitude - residual hearing - threshold
