Site of cochlear stimulation and its effect on electrically evoked compound action potentials using the MED-EL standard electrode array.
BACKGROUND
The standard electrode array for the MED-EL MAESTRO cochlear implant system is 31 mm in length which allows an insertion angle of approximately 720 degrees . When fully inserted, this long electrode array is capable of stimulating the most apical region of the cochlea. No investigation has explored Electrically Evoked Compound Action Potential (ECAP) recordings in this region with a large number of subjects using a commercially available cochlear implant system. The aim of this study is to determine if certain properties of ECAP recordings vary, depending on the stimulation site in the cochlea.


METHODS
Recordings of auditory nerve responses were conducted in 67 subjects to demonstrate the feasibility of ECAP recordings using the Auditory Nerve Response Telemetry (ART) feature of the MED-EL MAESTRO system software. These recordings were then analyzed based on the site of cochlear stimulation defined as basal, middle and apical to determine if the amplitude, threshold and slope of the amplitude growth function and the refractory time differs depending on the region of stimulation.


RESULTS
Findings show significant differences in the ECAP recordings depending on the stimulation site. Comparing the apical with the basal region, on average higher amplitudes, lower thresholds and steeper slopes of the amplitude growth function have been observed. The refractory time shows an overall dependence on cochlear region; however post-hoc tests showed no significant effect between individual regions.


CONCLUSIONS
Obtaining ECAP recordings is also possible in the most apical region of the cochlea. However, differences can be observed depending on the region of the cochlea stimulated. Specifically, significant higher ECAP amplitude, lower thresholds and steeper amplitude growth function slopes have been observed in the apical region. These differences could be explained by the location of the stimulating electrode with respect to the neural tissue in the cochlea, a higher density, or an increased neural survival rate of neural tissue in the apex.


BACKGROUND
The Clinical Investigation has the Competent Authority registration number DE/CA126/AP4/3332/18/05.
Brill
Stefan
S
Department of Otorhinolaryngology, Plastic, Aesthetic and Reconstructive Head and Neck Surgery, University of Wuerzburg, Würzburg, Germany. brill_s@klinik.uni-wuerzburg.de
Müller
Joachim
J
Hagen
Rudolf
R
Möltner
Alexander
A
Brockmeier
Steffi-Johanna
SJ
Stark
Thomas
T
Helbig
Silke
S
Maurer
Jan
J
Zahnert
Thomas
T
Zierhofer
Clemens
C
Nopp
Peter
P
Anderson
Ilona
I
Strahl
Stefan
S
D000200:Action Potentials; D000328:Adult; D000368:Aged; D003051:Cochlea / Q000502:physiology*; D003054:Cochlear Implants; D003056:Cochlear Nerve / Q000503:physiopathology*; D004558:Electric Stimulation; D004567:Electrodes, Implanted; D004867:Equipment Design; D005072:Evoked Potentials, Auditory; D005260:Female; D006319:Hearing Loss, Sensorineural / Q000503:physiopathology* / Q000628:therapy; D006801:Humans; D008297:Male; D008875:Middle Aged; D009928:Organ Specificity; D011930:Reaction Time; D055815:Young Adult