Piloting the recording of electrode voltages (REVS) using surface electrodes as a test to identify cochlear implant electrode migration, extra-cochlear electrodes and basal electrodes causing discomfort

Abstract

Objectives: To determine if Electrode Voltage (EV) measurements are potentially suitable as a test for detecting extra-cochlear electrodes in cochlear implants (CIs) and to analyse voltages developed in different stimulation modes. Methods: EV measurements were made using surface electrodes in live mode without averaging in 17 adult cochlear implant (CI) users (18 ears). The effect of stimulation level, the position of the active recording electrode, repeatability and the position of the implant's active electrode were investigated. For Nucleus recipients, measurements were made in different stimulation modes. Results/Discussion: Recordings made in monopolar mode showed good repeatability when the active recording electrode was placed on the ipsilateral earlobe; voltages increased linearly with stimulation level as expected. Basal electrode measurements differed greatly between fully inserted devices with all electrodes activated, partially inserted/migrated devices and fully inserted devices with deactivated basal electrodes [χ 2 (2)=10.2, p<0.05 for the most basal electrode]. Analysis of voltages measured in different stimulation modes found that EVs could be separated into two components, associated with the CI's active and return electrodes respectively. EVs for electrodes on the array were much smaller than those for monopolar return electrodes for fully inserted devices, but were abnormally large for one participant with extra-cochlear electrodes. We argue that fibrosis around the electrode array facilitated current flow across the round window in this case. Conclusion: The test appears to be a viable approach to detect electrode migration and extracochlear electrodes in adult CI users and may also be sensitive to discomfort caused by current leakage from the basal end of the cochlea.

Improving the sensitivity of cochlear implant integrity testing by recording electrode voltages with surface electrodes

“…This has a very high maximum sampling rate, 400 kHz, enabling even individual CI pulses to be captured in detail. CI stimulation was as in the previous study (Grasmeder et al, 2021): CIs were stimulated in live mode from the Soundwave software. A level of 79 charge units was used for both threshold (T) and most comfortable (M) levels, for all electrodes except E8, which was stimulated at 120 units to provide a "marker electrode" that allowed identification of electrode number in the resulting traces.…”

“…Our previous study (Grasmeder et al, 2021) identified differences in EVs between fully inserted and partially inserted electrode arrays and for different recording electrode positions. This finding is consistent with the observation that EVs are nonuniform across the array even for normally functioning devices when one of the recording electrodes is positioned on the ipsilateral side to the implant (Eitutis et al, 2022).…”

“…In a previous study (Grasmeder et al, 2021) we reported on recording electrode voltages (REVs) using surface electrodes without averaging. This method is considerably quicker than using averaging, as EVs for all the electrodes on the array can be recorded within a single time window of 10 ms.…”

“…There can also be differences in EV amplitudes for children of different ages (Garnham et al, 2001;Monin et al, 2006), whilst adults with fully inserted devices showed much less variability for the same stimulation mode (Grasmeder et al, 2021). If performance has deteriorated to the point where replacement of the device is deemed appropriate, there is a further opportunity to test the device once it has been explanted and returned to the manufacturer for analysis; it undergoes a series of tests to determine if it is faulty for regulatory purposes.…”

Detecting and managing partial shorts in Cochlear implants: A validation of scalp surface potential testing

“…Surface potentials measure electrical activity of the implant and are far larger than neural responses. More recently, Grasmeder applied a similar approach to detecting extra‐cochlear and migrating electrodes 10 . Here we present our clinical experience managing suspected Ultra V1 device faults detected using surface potentials.…”