Intraoperative findings on ECAP-measurement: Normal or special case?

Objective: This study aimed to investigate the measurability and threshold level of electrically evoked compound action potentials (ECAPs) in order to provide a baseline for the development of diagnostic references to support aftercare procedures. Design: In this retrospective study, cochlear implant patients were grouped according to the electrode array type and preoperative diagnostic findings from radiological imaging. ECAP measurements were performed intraoperatively on 22 electrodes for each patient resulting in two comparisons: (1) normal vs. pathological findings based on imaging with same electrode array, (2) perimodiolar electrode vs. straight electrode array within the normal group. Study sample: The study sample consisted of 218 ears with a Nucleus (R) implant. Results: In the group with normal radiological imaging, the percentage of measurable ECAPs was higher than in the pathological group. The ECAP thresholds on 21 electrodes were significantly different between the two groups. Furthermore the thresholds were significantly lower for basal electrodes mainly for the two different electrode types. Conclusion: The pathological changes in the inner ear, the type of electrode array, and the electrode position affect the ECAP threshold. Further consideration suggests that a receiver operating characteristic curve can be derived from the results.