Hearing preservation in CI, any predictors?
Reviewed by Hassan Mohammed

The electrically evoked compound action potential (eCAP), obtained non-invasively from cochlear implant (CI) recipients, represents a population response of the auditory nerve to electrical stimulation. The eCAP characteristics include threshold (the lower the better), growth of response (the steeper the better) and amplitude of response (the larger the better). The goals of this study included examining the effect of the type of the array (slim modiolar versus slim straight) on eCAP characteristics. It also investigated the potential clinical applications of intraoperative eCAP recordings for differentiating recipients who maintain residual hearing at the time of initial CI activation and predicting speech perception outcomes. Authors included 113 patients over a four-year period. Of these, 62 had CI 522 (straight) and 51 had CI 5232 (modiolar). The modiolar electrodes were inserted when the angle of insertion into the basal turn is favourable. The low frequency thresholds were roughly similar between the two groups. Hearing preservation (postop thresholds of <80 dB in low frequencies) was achieved in 51% of patients. Authors found that eCAP growth and amplitude were significantly affected by electrode location in relation to the modulus, especially the apical electrodes. A higher electrode impedance, on the other hand, was associated with lower eCAP growth. The results did not show a significant difference in eCAP characteristics between those who maintained their hearing at CI activation and those who did not. It also did not show the ability to predict speech perception outcomes. This study supports the previous literature findings. It differentiates between the multiple characteristics of eCAP. It demonstrated that suprathreshold measurements (growth and slope) seem to be more sensitive than threshold measurements in the apical electrodes. It would be beneficial to assess the changes in eCAP measurements over the years and their correlation with loss of low frequency hearing.

Intraoperative Electrically Evoked Compound Action Potential Growth and Maximum Amplitudes in Hearing Preservation Cochlear Implant Recipients.
Mussoi B, Woodson E, Sydlowski S.
OTOL NEUROTOL
2023;44(4):e216-22.