Abstract
Cochlear implants (CI) are the treatment of choice in profoundly deaf patients. Measuring the electrically evoked compound action potential (ECAP) has become an important tool for verifying the function of the spiral ganglion neurons (SGN), which are the target cells of the CI stimulation. ECAP measurement is only possible after electrode insertion. No information about the neuronal health status is available before cochlear implantation. We investigated possible correlations between the ECAP amplitude growth function (AGF) slope and anamnestic parameters to identify possible predictors for SGN health status and therefore for CI outcome. The study included patients being implanted with various electrode array lengths. Correlation analysis was performed for the mean AGF slope of the whole array, for separate electrodes as well as for grouped electrodes of the apical, medial, and basal region, with duration of deafness, age at implantation, residual hearing (grouped for electrode length), and etiology. The mean ECAP AGF slopes decreased from apical to basal. They were not correlated to the length of the electrode array or any etiology. For the mean of the full array or when grouped for the apical, middle, and basal part, the ECAP AGF slope was negatively correlated to the duration of hearing loss and the age at implantation. Since a significant negative correlation of the ECAP AGF slope and age at cochlear implantation and duration of deafness was observed, this study supports the statement that early implantation of a CI is recommended for sensorineural hearing loss. Additional factors such as the cochlear coverage and insertion angle influence the ECAP AGF slope and performance of the patient and should be included in future multifactorial analysis to study predictive parameters for the CI outcome.
Highlights
Worldwide, 466 million people suffer from disabling hearing loss with negative effects in social, emotional, and economic capacity due to a limited ability of communication [1].Patients with severe to profound sensorineural hearing loss are usually candidates to receive a cochlear implant (CI)
We investigated the correlation of the evoked compound action potential (ECAP) amplitude growth function (AGF) slope with the anamnestic parameters duration of deafness, age at implantation, etiology, and residual hearing
The mean ECAP AGF slope of all patients electrodes for analysis A = missing values set to 0 and analysis B = missing values excluded are 31.10 μV/nC and 37.26 μV/nC, respectively
Summary
Patients with severe to profound sensorineural hearing loss are usually candidates to receive a cochlear implant (CI). The CI’s electrode array is implanted into the scala tympani of the cochlea for electrical stimulation of the spiral ganglion neurons (SGN), which subsequently leads to sound perception (Figure 1). Other approaches focus on predicting post-operative outcomes using genetic factors [3]. Those methods can only make predictions within certain patient groups. The presence of a healthy and sufficiently large population of SGN that is able to transduce the encoded auditory information via the afferent auditory system to the auditory cortex has to be considered as prerequisite for cochlear implant outcome. The function and number of SGN correlates, at least in rodents, with the slopes of the electrically evoked compound action potential (ECAP) of the auditory nerve [4,5]
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