Postoperative Electrocochleography (ECochG) and Electrically Evoked Compound Action Potential (ECAP) in Hybrid Cochlear Implant Users: A Preliminary Study of its Feasibility to Predict Performance

Background: CI manufacturers have been redesigning their electrode arrays in order to preserve residual acoustic hearing. We hypothesize that success with these “Hybrid” CIs will depend on the ability of the user to perceive and integrate information transmitted acoustically and electrically.

Objective: It is possible to use the neural telemetry system of the Nucleus CI to record ECochG and ECAPs from Hybrid CI users. Our goal was to use these measures of the peripheral auditory function to characterize the status of the cochlea, and compare them to speech perception outcomes.

Method: ECochG and ECAPs were recorded from the most apical electrode in the Hybrid CI electrode array. Data from 10 Hybrid CI users has been collected to date. ECochG recordings were measured with 250, 500, 750, and 1000 Hz tone bursts presented in positive and negative polarity. These two recordings were subtracted to emphasize hair cell contributions (cochlear microphonic, CM/DIF) and added to emphasize neural contributions (auditory nerve neurophonic, ANN/SUM). ECAP growth functions were recorded using the standard subtraction method. ECochG and ECAP measures, audiometric thresholds, and performance on CNCs and AZBio sentences in noise were correlated.

Results: As expected, the ECochG thresholds were correlated with audiometric thresholds. Subjects with better hearing at 750-1000 Hz had more robust CM/DIF and ANN/SUM responses than subjects with less residual hearing. Measures of threshold and slope of the ECAP growth function were also correlated with audiometric thresholds. Correlations between these physiologic measures and speech perception are ongoing. Case reports focusing on outliers will be highlighted.

Supported by NIH/NIDCD P50 DC 000242.