Resident Physician Washington University in St. Louis
Objective: To determine the relationship of electrocochleography (ECochG) responses measured on the promontory with responses measured at the round window (RW) and various intracochlear sites. Also, verify that promontory ECochG responses correlate with postoperative speech-perception performance using the cochlear implant (CI).
Study Design: Prospective cohort study
Setting:Tertiary referral center
Patients and Interventions: Ninety-six adult CI recipients with no cochlear malformations or prior otologic surgery
Main Outcome Measures: Acoustically-evoked ECochG responses were measured intraoperatively at both extracochlear and intracochlear locations. ECochG total response (ECochG-TR), a measure of residual cochlear function, was calculated by summing the fast Fourier transformation amplitudes in response to a range of frequency stimuli (250Hz–2kHz). Speechperception performance (CNC) was measured at 6-months.
Results: There were strong linear correlations for promontory ECochG-TR with the ECochG-TRs measured at the RW (r= 0.95; p<0.0001), just inside scala tympani (r = 0.91; p<0.0001), and after full insertion (r = 0.83; p<0.0001). For an individual subject, the waveforms of the ECochG response were similar in character across all positions; however, the response amplitude increased from promontory to RW (~1.4-fold) to just inside scala tympani (~2-fold), with the largest response at full insertion (~2.5-fold). RW ECochG-TR independently explained 61.0% of the variability (r2) in CNC at 6 months.
Conclusions: Promontory ECochG recordings are feasible in most CI recipients and explain a substantial portion of the variability in CI performance. These findings are a critical step in supporting translation of trans-tympanic ECochG into the clinic preoperatively to help predict postoperative CI performance.
*Professional Practice Gap & Educational Need: Recognizing factors that affect CI performance at a preoperative candidacy level may have drastic implications on post-CI aural rehabilitation, device design and fitting, and surgical technique. Age at implantation, duration of hearing loss, and electrode positioning within the cochlea together explain less than 25% of the variability in speech-perception scores in quiet, making these poor indicators. ECochG responses, prior to implantation at the RW, account for ~50% of the variability in the same speech-perception measures. Prior studies have not investigated whether ECochG responses can be measured on the promontory, a more clinically accessible site.
*Learning Objective: To determine whether acoustically-evoked ECochG responses measured on the promontory correlated with responses measured at other extracochlear and intracochlear sites. To assess whether ECochG responses can be used to explain the variability in postoperative CI performance.
*Desired Result: Practitioners and researchers will further realize the feasibility and value of performing promontory ECochG recordings in CI patients, including those with no-response audiograms and understand the potential of using these responses to predict CI performance.
*Level of Evidence: IV
*Indicate IRB or IACUC: Washington University in St. Louis IRB #202007087.