Monitoring Cochlear Health With Intracochlear Electrocochleography During Cochlear Implantation: Findings From an International Clinical Investigation

S O'Leary, E Mylanus, F Venail, T Lenarz, C Birman, F Di Lella, J T Roland Jr, B Gantz, A Beynon, M Sicard, A Buechner, W K Lai, C Boccio, B Choudhury, V D Tejani, K Plant, R English, R Arts, C Bester, S O'Leary, E Mylanus, F Venail, T Lenarz, C Birman, F Di Lella, J T Roland Jr, B Gantz, A Beynon, M Sicard, A Buechner, W K Lai, C Boccio, B Choudhury, V D Tejani, K Plant, R English, R Arts, C Bester

Abstract

Objectives: Electrocochleography (ECochG) is emerging as a tool for monitoring cochlear function during cochlear implant (CI) surgery. ECochG may be recorded directly from electrodes on the implant array intraoperatively. For low-frequency stimulation, its amplitude tends to rise or may plateau as the electrode is inserted. The aim of this study was to explore whether compromise of the ECochG signal, defined as a fall in its amplitude of 30% or more during insertion, whether transient or permanent, is associated with poorer postoperative acoustic hearing, and to examine how preoperative hearing levels may influence the ability to record ECochG. The specific hypotheses tested were threefold: (a) deterioration in the pure-tone average of low-frequency hearing at the first postoperative follow-up interval (follow-up visit 1 [FUV1], 4 to 6 weeks) will be associated with compromise of the cochlear microphonic (CM) amplitude during electrode insertion (primary hypothesis); (b) an association is observed at the second postoperative follow-up interval (FUV2, 3 months) (secondary hypothesis 1); and (c) the CM response will be recorded earlier during electrode array insertion when the preoperative high-frequency hearing is better (secondary hypothesis 2).

Design: International, multi-site prospective, observational, between groups design, targeting 41 adult participants in each of two groups, (compromised CM versus preserved CM). Adult CI candidates who were scheduled to receive a Cochlear Nucleus CI with a Slim Straight or a Slim Modiolar electrode array and had a preoperative audiometric low-frequency average thresholds of ≤80 dB HL at 500, 750, and 1000 Hz in the ear to be implanted, were recruited from eight international implant sites. Pure tone audiometry was measured preoperatively and at postoperative visits (FUV1 and follow-up visit 2 [FUV2]). ECochG was measured during and immediately after the implantation of the array.

Results: From a total of 78 enrolled individuals (80 ears), 77 participants (79 ears) underwent surgery. Due to protocol deviations, 18 ears (23%) were excluded. Of the 61 ears with ECochG responses, amplitudes were < 1 µV throughout implantation for 18 ears (23%) and deemed "unclear" for classification. EcochG responses >1 µV in 43 ears (55%) were stable throughout implantation for 8 ears and compromised in 35 ears. For the primary endpoint at FUV1, 7/41 ears (17%) with preserved CM had a median hearing loss of 12.6 dB versus 34/41 ears (83%) with compromised CM and a median hearing loss of 26.9 dB ( p < 0.014). In assessing the practicalities of measuring intraoperative ECochG, the presence of a measurable CM (>1 µV) during implantation was dependent on preoperative, low-frequency thresholds, particularly at the stimulus frequency (0.5 kHz). High-frequency, preoperative thresholds were also associated with a measurable CM > 1 µV during surgery.

Conclusions: Our data shows that CM drops occurring during electrode insertion were correlated with significantly poorer hearing preservation postoperatively compared to CMs that remained stable throughout the electrode insertion. The practicality of measuring ECochG in a large cohort is discussed, regarding the suggested optimal preoperative low-frequency hearing levels ( < 80 dB HL) considered necessary to obtain a CM signal >1 µV.

Conflict of interest statement

K. P., R. E., and R. A. are Cochlear employees. B. G. is a consultant to Cochlear Corporation and EarLens Corporation. F. V. has been granted by the « Fondation pour l’Audition « (RD- 2020-10). Stephen O’Leary was funded by the National Health and Medical Research Council (Australia), GNT0628679 and GNT1078673. Stephen O’Leary and Christofer Bester’s department of Otolaryngology at the University of Melbourne received research grants from Cochlear Ltd. All the other authors have no conflicts of interest to disclose.

Copyright © 2022 The Authors. Ear & Hearing is published on behalf of the American Auditory Society, by Wolters Kluwer Health, Inc.

Figures

Fig. 1.
Fig. 1.
Participant recruitment and evaluation pathway.
Fig. 2.
Fig. 2.
Left panels, examples of preserved CM in two participants. Small fluctuations

Fig. 3.

Left panels, examples of compromised…

Fig. 3.

Left panels, examples of compromised CM in two participants. Large CM drops as…

Fig. 3.
Left panels, examples of compromised CM in two participants. Large CM drops as indicated by the slim arrows occur often during implantation, as well as when manipulating the electrode after full insertion. Only one drop has been shown with an arrow. Upper panel, CM drop occurs from 17 to 22 sec, with CM amplitude reduced from 5.5 to 1.0 μV. Lower panel, CM drop occurs from 83 to 134 sec, with an amplitude drop from 2.6 to 0.9 μV. Thick arrow represents point of complete insertion. Right panels, waveforms from traces on the left at timepoints shown at 1, 2, and 3. CM indicates cochlear microphonic.

Fig. 4.

Left panels, examples of compromised…

Fig. 4.

Left panels, examples of compromised CM in two participants. Any drop >30% maximum…

Fig. 4.
Left panels, examples of compromised CM in two participants. Any drop >30% maximum amplitude as indicated by the slim arrows immediately classifies the participant as having a compromised CM. Upper panel, CM drop occurs from 37 to 64 sec, with CM amplitude reduced from 3.5 to 0.8 μV. Lower panel, CM drop occurs from 219 to 231 sec, with an amplitude drop from 19.5 to 8.7 μV. Thick arrows represent point of complete insertion. Right panels, waveforms from traces on the left at timepoints shown at 1, 2, and 3. CM indicates cochlear microphonic.

Fig. 5.

Pre-op to FUV1 mean threshold…

Fig. 5.

Pre-op to FUV1 mean threshold deterioration (dB) for the preserved CM (No Drop)…

Fig. 5.
Pre-op to FUV1 mean threshold deterioration (dB) for the preserved CM (No Drop) (n = 7 ears) and compromised CM (Drop) (n = 34 ears) groups (*p < 0.05). Red cross for outliers, automatically calculated as those points exceeding the 75th percentile plus 1.5 times 75th percentile minus the 25th percentile. CM indicates cochlear microphonic; FUV, follow-up visit.

Fig. 6.

Pre-op to FUV2 threshold deterioration…

Fig. 6.

Pre-op to FUV2 threshold deterioration (dB) for the preserved CM (No Drop, n…

Fig. 6.
Pre-op to FUV2 threshold deterioration (dB) for the preserved CM (No Drop, n = 8 ears) and compromised CM (Drop, n = 30 ears) groups (**p < 0.01). Red cross for outliers, automatically calculated as those points exceeding the 75th percentile plus 1.5 times 75th percentile minus the 25th percentile. CM indicates cochlear microphonic; FUV, follow-up visit.

Fig. 7.

Relationship between high-frequency thresholds (in…

Fig. 7.

Relationship between high-frequency thresholds (in dB HL) at POV1 and onset of CM…

Fig. 7.
Relationship between high-frequency thresholds (in dB HL) at POV1 and onset of CM response measured in terms of number of electrodes inserted before a CM was detected. N = 36 ears. CM indicates cochlear microphonic; POV, preoperative visit.

Fig. 8.

Low-frequency average hearing loss (dB)…

Fig. 8.

Low-frequency average hearing loss (dB) at FUV1 for the transient drop (n =…

Fig. 8.
Low-frequency average hearing loss (dB) at FUV1 for the transient drop (n = 8 ears) and permanent drop CM groups (n = 30 ears). Red cross for outlier. CM indicates cochlear microphonic; FUV, follow-up visit.

Fig. 9.

Preoperative pure tone thresholds (dB…

Fig. 9.

Preoperative pure tone thresholds (dB HL) grouped according to whether the CM was…

Fig. 9.
Preoperative pure tone thresholds (dB HL) grouped according to whether the CM was present (P) or absent (A) at a particular frequency, n = 61 ears. Significantly better mean preoperative thresholds for the CM present group are indicated at 0.25, 0.5, 0.75, 1, and 2 kHz. (* p < 0.05), (*** p < 0.001). Red cross for outliers, automatically calculated as those points exceeding the 75th percentile plus 1.5 times 75th percentile minus the 25th percentile. CM indicates cochlear microphonic.
All figures (9)
Fig. 3.
Fig. 3.
Left panels, examples of compromised CM in two participants. Large CM drops as indicated by the slim arrows occur often during implantation, as well as when manipulating the electrode after full insertion. Only one drop has been shown with an arrow. Upper panel, CM drop occurs from 17 to 22 sec, with CM amplitude reduced from 5.5 to 1.0 μV. Lower panel, CM drop occurs from 83 to 134 sec, with an amplitude drop from 2.6 to 0.9 μV. Thick arrow represents point of complete insertion. Right panels, waveforms from traces on the left at timepoints shown at 1, 2, and 3. CM indicates cochlear microphonic.
Fig. 4.
Fig. 4.
Left panels, examples of compromised CM in two participants. Any drop >30% maximum amplitude as indicated by the slim arrows immediately classifies the participant as having a compromised CM. Upper panel, CM drop occurs from 37 to 64 sec, with CM amplitude reduced from 3.5 to 0.8 μV. Lower panel, CM drop occurs from 219 to 231 sec, with an amplitude drop from 19.5 to 8.7 μV. Thick arrows represent point of complete insertion. Right panels, waveforms from traces on the left at timepoints shown at 1, 2, and 3. CM indicates cochlear microphonic.
Fig. 5.
Fig. 5.
Pre-op to FUV1 mean threshold deterioration (dB) for the preserved CM (No Drop) (n = 7 ears) and compromised CM (Drop) (n = 34 ears) groups (*p < 0.05). Red cross for outliers, automatically calculated as those points exceeding the 75th percentile plus 1.5 times 75th percentile minus the 25th percentile. CM indicates cochlear microphonic; FUV, follow-up visit.
Fig. 6.
Fig. 6.
Pre-op to FUV2 threshold deterioration (dB) for the preserved CM (No Drop, n = 8 ears) and compromised CM (Drop, n = 30 ears) groups (**p < 0.01). Red cross for outliers, automatically calculated as those points exceeding the 75th percentile plus 1.5 times 75th percentile minus the 25th percentile. CM indicates cochlear microphonic; FUV, follow-up visit.
Fig. 7.
Fig. 7.
Relationship between high-frequency thresholds (in dB HL) at POV1 and onset of CM response measured in terms of number of electrodes inserted before a CM was detected. N = 36 ears. CM indicates cochlear microphonic; POV, preoperative visit.
Fig. 8.
Fig. 8.
Low-frequency average hearing loss (dB) at FUV1 for the transient drop (n = 8 ears) and permanent drop CM groups (n = 30 ears). Red cross for outlier. CM indicates cochlear microphonic; FUV, follow-up visit.
Fig. 9.
Fig. 9.
Preoperative pure tone thresholds (dB HL) grouped according to whether the CM was present (P) or absent (A) at a particular frequency, n = 61 ears. Significantly better mean preoperative thresholds for the CM present group are indicated at 0.25, 0.5, 0.75, 1, and 2 kHz. (* p < 0.05), (*** p < 0.001). Red cross for outliers, automatically calculated as those points exceeding the 75th percentile plus 1.5 times 75th percentile minus the 25th percentile. CM indicates cochlear microphonic.

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