Slope of electrically evoked compound action potential amplitude growth function is site-dependent

Objectives In human cochlear implant (CI) recipients, the slope of the electrically evoked compound action potential (ECAP) amplitude growth function (AGF) is not very well investigated, in comparison to the threshold derived from the AGF. This is despite the fact that it was shown in animal experiments that the slope correlates with the number of excitable neurons. The rationale of this study was to establish baseline data of the AGF slope for possible clinical applications, while investigating stability over time and dependence on cochlear site. Design ECAP AGFs of 16 ears implanted with MED-EL CIs were recorded on all electrode contacts during the normal clinical routine at 4 different points in time. Results Due to patient availability, not all 16 ears could be measured at all 4 points in time. A dependence of the slope on the electrode position was visible and statistically significant: At the three electrode contacts at the apical end of the array, the slope is greater compared to the medial and basal region of the cochlea. Conclusion The three most apical electrode contacts show greater slopes of ECAP AGF recordings. Our data of the cohort slopes show mild effects between the 4 different points in time.