Relationship Between Intraoperative Electrocochleography and Hearing Preservation

Abstract

Objectives: To compare intraoperative intracochlear electrocochleography (ECochG) with hearing preservation outcomes in cochlear implant (CI) subjects.

Design: Intraoperative electrocochleography was performed in adult CI subjects who were recipients of Advanced Bionics' Bionics LLC precurved HiFocus MidScala or straight HiFocus SlimJ electrode arrays. ECochG responses were recorded from the most apical electrode contact during insertion. No changes to the insertions were made due to ECochG monitoring. No information about insertion resistance was collected. ECochG drops were estimated as the change in amplitude from peak (defined as maximum amplitude response) to drop (largest drop) point after the peak during insertion was measured following the peak response. Audiometric thresholds from each subject were obtained before and approximately 1 month after CI surgery. The change in pure tone average for frequencies between 125 Hz and 500 Hz was measured after surgery. No postoperative CT scans were collected as part of this study.

Results: A total of 68 subjects from five surgical centers participated in the study. The study sample included 30 MidScala and 38 SlimJ electrodes implanted by approximately 20 surgeons who contributed to the study. Although a wide range of results were observed, there was a moderate positive correlation (Pearson Correlation coefficient, r = 0.56, p < 0.01) between the size of the ECochG drop and the magnitude of pure tone average change. This trend was present for both the MidScala and SlimJ arrays. The SlimJ and MidScala arrays produced significantly different hearing loss after surgery.

Conclusion: Large ECochG amplitude drops observed during electrode insertion indicated poorer hearing preservation. Although the outcomes were variable, this information may be helpful to guide surgical decision-making when contemplating full electrode insertion and the likelihood of hearing preservation.

Figure 1.

Example of an ECochG response to a 500 Hz tone burst at 110 dB SPL. Panels A, B, C and D show four representative insertion tracks. Panel A: Insertion track with notations shown as representative markers. RW indicates the start of insertion at RW, Peak indicates the maximum peak observed during insertion, Drop indicates the Drop observed after the maximum peak, Final indicates the amplitude at the end of insertion. Amplitude drops were 18.2, 22, 5.8 and 0.5 dB for panels A, B, C, and D, respectively.

Figure 2.

Panel A: PTA change is shown as a function of largest ECochG amplitude drop in dB with a linear fitted line. Outliers are circled with the top left two (same circle) translocations, the bottom left an increase in PTA after insertion, and the bottom right a significant shift of transmitting wire after electrode insertion. Panel B: PTA change is shown as a function of pre-operative PTA and linear fitted line.

Figure 3.

Panel A: PTA change is shown as a function of the largest ECochG drop for different electrode array types. Closed circles indicate MidScala and open circles indicate SlimJ electrode types. Panel B: Pre-operative PTA is shown as a function of Post-operative PTA with diagonal line indicating no change, dotted line indicating 15dB change and dashed line 30dB change. Closed circles indicate MidScala and open circles indicate SlimJ electrode types.