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).

Methods

EV measurements were made using surface electrodes in live mode in 17 adult cochlear implant (CI) users. Repeatability, the effects of stimulation level, CI active electrode position, (active) recording electrode position and stimulation mode (for Nucleus devices) were investigated.

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. EVs for basal electrodes differed greatly between partially inserted/migrated devices, fully inserted devices with all electrodes activated, and those with deactivated basal electrodes [χ²(2) = 10.2, p < 0.05 for the most basal electrode]. EVs for Nucleus devices were small for electrodes on the array when compared to those for monopolar return electrodes, except for the 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 extra-cochlear electrodes in adult CI users and may also be sensitive to discomfort caused by current leakage from the basal end of the cochlea.

Keywords:

• Cochlear implant
• Electrode
• Voltage
• Integrity test
• Partial insertion
• Migration
• Extra-cochlear
• Fibrosis

Acknowledgements

The authors would like to thank Dr Patrick Boyle of Advanced Bionics and Dr Barry Nevison of Cochlear Europe Ltd for their advice on measuring electrode voltages with implants manufactured by the companies which they represent.

Disclaimer statements

Contributors None.

Conflict of interest None.

Ethics approval None.

Additional information

Funding

This work was supported by Engineering and Physical Sciences Research Council: [Grant Number 1649359]