Toward a Better Understanding of Electrocochleography: Analysis of Real-Time Recordings

Abstract

Objectives: Real-time electrocochleography (ECochG) has been used as a monitoring tool during cochlear implantation (CI), whereby, amplitude drops have been correlated with postoperative acoustic hearing results. However, no consensus has been reached as to how a single event of an amplitude drop should be characterized. The aim of this study was to identify ECochG events that predict loss of hearing 1 month after surgery. Design: Fifty-five patients were included in this prospective cohort study. Real-time ECochG measurements were performed during CI electrode insertion. Single ECochG events were characterized according to their amplitude loss and slope steepness. Results: Using receiver operating characteristic analyses, the most efficient cut-off criterion for a relative hearing loss of 25% was an amplitude loss of 61% at a fixed slope steepness of 0.2 µV/sec. Three-quarters of our population had at least one such event during implantation. Most events occurred shortly before full insertion. With increasing number of events, median residual hearing thresholds deteriorated for all frequencies. Larger amplitude drops trended toward worse hearing preservation. Signal recovery after an ECochG event could not be correlated to acoustic hearing outcomes. Conclusions: Our data suggest that amplitude drops exceeding 61% of the ongoing signal at a slope steepness of 0.2 µV/sec are correlated with worse acoustic hearing preservation. Clearly defined ECochG events have the potential to guide surgeons during CI in the future. This is essential if a fully automated data analysis is to be employed or benchmarking undertaken.

Real Time Monitoring During Cochlear Implantation: Increasing the Accuracy of Predicting Residual Hearing Outcomes

“…In our figures, the relative signal recovery after an ECochG event was not linearly correlated to the acoustic hearing outcome. This corroborates earlier findings (3). In contrast to that, Campbell et al (1) described better acoustic hearing results, if CM amplitudes recovered after an amplitude drop.…”

“…Measurement setup and data collection was identical with the method described in our previous article (3). In short, an Etymotics ER3A transducer (3 M, USA) and E-A-RLINK Foam Ear Tip 3B (3 M, USA) delivered the acoustic stimuli (tone pip at 500 Hz with alternating polarities).…”

“…During intracochlear monitoring, an amplitude drop of the cochlear microphonic (CM) signal has been correlated with poorer preservation of residual hearing (1,2). In our previous work, we reported that an instantaneous drop in amplitude exceeding 61% with a slope steepness of 0.2 mV/s or greater (an ''ECochG event'') was associated with poorer residual hearing in the postoperative period (3). If there was no ECochG event, residual hearing was preserved in almost all cases, whereas patients experiencing multiple events routinely lost their acoustic hearing.…”

Intraoperative Observational Real-time Electrocochleography as a Predictor of Hearing Loss After Cochlear Implantation: 3 and 12 Month Outcomes

“…Similarly, the sometimes rapid ECochG fluctuations seen here are not often observed in extracochlear ECochG recordings ( 3 ), where very different patterns of ECochG amplitude loss and recovery are encountered. It is clearly argued in Weder et al ( 19 ) that these transient drops have just as significant an effect on postoperative hearing preservation as permanent drops. It seems likely, therefore, that the observations made here may not be directly applicable to the extracochlear ECochG approaches.…”

Performing Intracochlear Electrocochleography During Cochlear Implantation

“…A randomized study showed that when the CM amplitude decreased by 30% or more (related to the initial maximum amplitude), a slight withdrawal of the electrode resulted in a significant improvement of postoperative residual hearing 21 . However, the definition of a detrimental drop is unclear; another publication reported a CM decrease of 61% (or more) at a slope steepness of 0.2 µV/ s (or more) to be significant 9 . A drop in ECochG responses may also be due to other causes, such as the interaction of different signal generators, passing the 500 Hz range within the cochlea, or contact of the basilar membrane with the electrode array 6 , 24 .…”