Intraoperative Electrically Evoked Compound Action Potential (ECAP) Measurements in Traditional and Hearing Preservation Cochlear Implantation

Abstract

In current practice, the status of residual low-frequency acoustic hearing in hearing preservation cochlear implantation (CI) is unknown until activation two to three weeks postoperatively. The intraoperatively measured electrically evoked compound action potential (ECAP), a synchronous response from electrically stimulated auditory nerve fibers, is one of the first markers of auditory nerve function after cochlear implant surgery and such may provide information regarding the status of residual low-frequency acoustic hearing.This study aimed to evaluate the relationship between intraoperative ECAP at the time of CI and presence of preoperative and postoperative low-frequency acoustic hearing.A retrospective case review.Two hundred seventeen adult ears receiving CI (42 Advanced Bionics, 82 Cochlear, and 93 MED-EL implants).Intraoperative ECAP and CI.ECAP measurements were obtained intraoperatively, whereas residual hearing data were obtained from postoperative CI activation audiogram. A linear mixed model test revealed no interaction effects for the following variables: manufacturer, electrode location (basal, middle, and apical), preoperative low-frequency pure-tone average (LFPTA), and postoperative LFPTA. The postoperative residual low-frequency hearing status was defined as preservation of unaided air conduction thresholds ≤90 dB at 250 Hz. Electrode location and hearing preservation data were analyzed individually for both the ECAP threshold and ECAP maximum amplitude using multiple t-tests, without assuming a consistent standard deviation between the groups, and with alpha correction.The maximum amplitude, in microvolts, was significantly higher throughout apical and middle regions of the cochlea in patients who had preserved low-frequency acoustic hearing as compared with those who did not have preserved hearing (p = 0.0001 and p = 0.0088, respectively). ECAP threshold, in microamperes, was significantly lower throughout the apical region of the cochlea in patients with preserved low-frequency acoustic hearing as compared with those without preserved hearing (p = 0.0099). Basal electrode maximum amplitudes and middle and basal electrode thresholds were not significantly correlated with postoperative low-frequency hearing.Apical and middle electrode maximum amplitudes and apical electrode thresholds detected through intraoperative ECAP measurements are significantly correlated with preservation of low-frequency acoustic hearing. This association may represent a potential immediate feedback mechanism for postoperative outcomes that can be applied to all CIs.

Intraoperative Electrically Evoked Compound Action Potential Growth and Maximum Amplitudes in Hearing Preservation Cochlear Implant Recipients

“…Thus, it seems that these eCAP metrics cannot be used to predict the success of hearing preservation surgery. This finding is in contrast with the findings of a recent study, showing that recipients with successful hearing preservation had larger eCAP maximum amplitudes and lower eCAP thresholds (all three CI manufacturers were represented) (21). This discrepancy may be related to how hearing preservation was defined.…”

“…The present study followed the criteria suggested by the American Academy of Otolaryngology–Head and Neck Surgery (22), that is, LFPTA ≤80 dB HL, whereas Nassiri and colleagues (21) defined hearing preservation as a threshold of ≤90 dB HL at 250 Hz only. Another key distinction between these two reports is that the present study only focused on recipients who were hearing preservation candidates, whereas the study by Nassiri and colleagues (21) also included traditional CI candidates in their sample, who, by virtue of their greater degree of preoperative low-frequency hearing loss, are more likely to have poorer neural survival at the cochlear apex (although their findings remained when comparing only the two groups with preoperative residual hearing). Short-term loss of residual hearing is thought to be a result of mechanical trauma from insertion of the electrode array, which is followed by an inflammatory response (34).…”

“…However, it is possible that with the broadening of CI candidacy guidelines to include recipients with more residual hearing and the development of soft surgical techniques and advanced electrode array designs, intraoperative eCAP recordings may have increased clinical utility. For example, it has been proposed that intraoperative eCAP recordings could be used to identify recipients who are more likely to maintain postoperative residual hearing, as these recipients have been shown to have larger eCAP amplitudes and lower eCAP thresholds at the cochlear apex than those who lost residual hearing at initial activation or were not hearing preservation candidates (21).…”

Cochlear protein biomarkers as potential sites for targeted inner ear drug delivery

“…There are layers of complexity to each step of this process that necessitate discussion. From a clinical perspective, it is a risk to initiate treatment on subjects who have any residual cochlear function because the cochlear cells are particularly sensitive to changes within the local environment [96,97]. Thus, many subjects with acquired forms of otologic insult and some remaining natural hearing are unlikely to be candidates in clinical trials for the initiation of targeted treatments [98].…”

Electrically evoked compound action potentials in cochlear implant users with preoperative residual hearing

“…The study of Nassiri et al (2019) showed significant differences in ECAP measures in a large number of CI recipients with and without residual hearing. Residual hearing was defined as unaided air conduction threshold ≤90 dB HL at 250 Hz at CI activation.…”