Early Hearing Preservation Outcomes Following Cochlear Implantation with New Slim Lateral Wall Electrode Using Electrocochleography

Abstract

Objective:

Describe early hearing preservation (HP) cochlear implantation (CI) outcomes using a new slim lateral wall electrode (SLWE).

Study Design:

Prospective cohort study.

Setting:

Tertiary referral center.

Patients:

Adult CI candidates with preoperative low-frequency pure tone average (LFPTA; 125, 250, 500Hz) ≤60 dB HL

Intervention(s):

CI with and without intracochlear real-time electrocochleography (RT-ECochG)

Main Outcome Measure(s):

HP (LFPTA ≤80dB HL), LFPTA shift, speech-perception performance measures, postoperative CT reconstruction

Results:

Forty-two subjects were implanted with the SLWE. Thirty patients underwent full insertion without RT-ECochG feedback, and HP was maintained at 3-months postactivation for 7 (23.3%) patients with mean LFPTA shift of 57.5 ± 25.6 dB HL. RT-ECochG feedback was utilized on 12 patients, of which 6 patients had full insertions and 6 patients had anywhere from 1–3 electrodes left outside of the cochlea based on RT-ECochG feedback. At 3-months postoperatively, HP was achieved on 10 (83.3%) patients and mean LFPTA shift was 18.9 c 11.7 dB HL. Mean difference between LFPTA threshold shift at 3-months postactivation with and without RT-ECochG was 38.6 dB HL (95% CI, 25.6 – 51.67). There was an improvement in delta CNC from preoperative to 3-months postactivation when using RT-ECochG, with mean difference 20.7% (95% CI, 3.3 to 38.1).

Conclusions:

Use of RT-ECochG monitoring during SLWE placement results in fewer full electrode insertions and significantly better HP rates and speech-perception outcomes when compared to unmonitored insertions. Further investigation is needed to evaluate long-term audiologic outcomes to better understand the relationships among ECochG, cochlear trauma, functional outcomes, and HP.

INTRODUCTION:

Cochlear implantation (CI) aims to restore auditory perception in patients with severe-to-profound hearing loss that no longer benefit from amplification. The candidacy criteria for CI continues to broaden with a greater emphasis on patients with functional low-frequency hearing and poor monosyllabic speech understanding. Recent studies have shown that low-frequency hearing can be preserved after CI with various electrode types.^1–11 However, significant debate remains over the ideal electrode and surgical approach that can consistently provide reliable hearing preservation (HP) outcomes while optimizing speech-perception performance in patients with preservable hearing.

Shorter lateral wall arrays are considered to be more appropriate for patients with low-frequency hearing because of reduced apical intracochlear trauma and translocation.^12–14 Conversely, longer arrays are better suited for patients with little to no low-frequency hearing because the deeply inserted array is in closer alignment with natural place coding within the cochlea.^15–18 Often the preoperative decision process must balance the risks and benefits of selecting a shorter array for preserving acoustic hearing or a longer array for maximal cochlear coverage if acoustic hearing is lost.

Electrode choice likely depends on a patient’s preoperative hearing, cochlear anatomy, and whether residual hearing will be used for electroacoustic stimulation. Recent studies have shown that cochlear duct lengths vary across patients and the ideal insertion depth may be patient-specific.^19,20 Hollis et al showed that CI candidates with low-frequency hearing and short cochlear duct lengths were at greater risk of losing their residual hearing after CI when standard length electrodes were used.²¹ These findings suggest that accounting for the patient’s cochlear duct length may be required for electrode selection to maximize both HP outcomes and cochlear coverage.

Electrocochleography (ECochG) is a measure of cochlear functional integrity that can inform potential intracochlear trauma during electrode insertion.^22,23 This entails recording acoustically evoked electrical potentials generated by the auditory nerve and inner ear. Prior studies have evaluated the utility of ECochG responses intraoperatively recorded from the CI array itself in patients with low-frequency hearing, demonstrating a correlation between ECochG responses and presence of postoperative acoustic hearing.^22,24 Unfortunately, the correlation between ECochG measures and postoperative hearing outcomes vary among studies.^25–27 These inconsistencies may be a result of the heterogeneity of recording parameters between studies and small sample sizes. To our knowledge, no study has compared HP outcomes with and without the use of intraoperative real-time ECochG (RT-ECochG).

Slim lateral wall electrodes (SLWE) were designed to optimize cochlear coverage and maximize HP. The primary objective of this study was to report on HP outcomes from a cohort of patients consecutively implanted with a newly designed SLWE with and without RT-ECochG. No study to date has reported HP outcomes using this new SLWE. Secondary objectives were to report on insertion depth and whether RT-ECochG could improve early HP outcomes with this new array. Based on poor early HP outcomes and large LFPTA shifts without any type of feedback during insertion, we hypothesized that feedback derived from RT-ECochG can improve HP outcomes in patients by determining the ideal insertion depth based on changes in ECochG responses.

MATERIALS AND METHODS:

Participants:

This study was approved by the institutional review board at Washington University (IRB #202006179). Thirty-eight post-lingual adults were implanted consecutively with the CI624 fitted with the new Slim 20 lateral wall electrode (Cochlear Corp, Sydney, AU) between July 2020 and June 2021. Details on electrode design are presented in Figure 1. Patients were offered the SLWE if they had a low frequency pure-tone average (LFPTA; 125, 250, and 500Hz) ≤ 60dB HL and normal cochlear anatomy. Demographic information including age, sex, side of implantation, and duration of hearing loss were collected at the time of study recruitment (Table 1).

FIGURE 1:

Dimensions of the new slim lateral wall electrode are shown. The electrode diameter is smaller than that of the scala tympani within the cochlea to minimize the risk of trauma to intracochlear structures.

TABLE 1:

Demographic information for all 42 patients implanted with the new slim lateral wall electrode.

	Mean +/− STD or N (%)
Age (Years)	74.1 ± 15.3
Gender (% male)	25 (59.5%)
Duration of Hearing Loss (Years)	24.0 ± 12.7
Duration of Severe/Profound Hearing Loss (Years)	10.6 ± 7.1
Single-sided Deafness	4 (9.5%)
Etiology
Meniere’s Disease	2 (4.8%)
Noise Exposure	4 (9.4%)
Sudden Sensorineural Hearing Loss	2 (4.8%)
Meningitis	1 (2.4%)
Otosclerosis	1 (2.4%)
Progressive	15 (35.7%)
Unknown	17 (40.5%)
Tip Fold-Over	0
Duration of Hearing Aid Use (Years)	13.9 ± 11.4
Prior Hearing Aid Use	36 (85.7%)

Operative details:

Cochlear implantation was performed using standard mastoidectomy with a facial recess approach to access the round window (RW). The RW membrane was visualized by removing the bony overhang. Placement of the SLWE was performed through an anteroinferior RW approach; the RW was fenestrated with a 0.6 mm diameter perforator. Without RT-ECochG, electrode insertion was slow (~30 seconds) utilizing standard electrode forceps, with the goal of minimizing trauma. Implantation was performed by four different surgeons, with ~80% performed by the senior author in both patient cohorts. Decadron was applied to the RW after array insertion, and all patients received both intraoperative and postoperative steroids. Hearing preservation practices vary across institutions including use of steroids, lubricating agents for insertion, and insertion times.²⁸ In our practice, for hearing preservation cases, we use steroids at the round window after insertion, insertion times (≥ 30 seconds), and do not use a lubricating agent.

Use of ECochG & Signal Analysis:

The residual hearing was monitored in 12 patients during insertion by RT-ECochG. The surgeons received feedback on any amplitude changes of the cochlear microphonic (CM) at the stimulus frequency. The motivation for RT-ECochG monitoring was based on poor early HP outcomes for the first 30 subjects. No further modifications (e.g., steroid administration, lubricant use, etc.) were made in the hearing preservation approach for the RT-ECochG patient cohort.

All ECochG measurements were recorded using the Cochlear Research Platform (v1.2). ECochG potentials were measured from the most apical electrode of the implant. Intraoperatively, an E.A. ETONE 3A (Earphone, Auditory System) insert earphone was placed in the external auditory canal. Extracochlear recordings using the ground electrode were first performed to determine whether 250 Hz or 500 Hz was used for the acoustic stimulus during insertion. Prior to opening the RW, the ground electrode was placed on the RW membrane and measurements at 250 and 500 Hz were performed with 100 sweeps. Tone bursts were 20 ms long and 1 ms rise/fall times at 108 dB HL, presented at 14/second and with alternating polarities, 50-ms interstimulus interval with 1-ms onset/offset ramp time. A sample rate of 20.9 kHz was used to acquire the responses over a 12.5 ms recording duration through back-telemetry.

ECochG responses were then exported to MATLAB (MathWorks, Natick, MA) where it was analyzed, postoperatively. The Cochlear Research Platform is able to measure the CM in real-time by performing a fast Fourier transformation for the difference trace and calculating the amplitude of the response at the stimulating frequency. These are the measurements that are used to provide intraoperative feedback on potential intracochlear trauma.

Consensus on RT-ECochG Feedback:

Consensus amongst surgeons was to insert at minimum 17 of the 22 electrodes, and the last 5 electrodes were up to the surgeon’s discretion based on RT-ECochG feedback. A drop of the CM signal > 5 μV was considered a consequence of electrode interfering with basilar membrane movement. In response to a drop in response, electrode insertion was stopped, and the surgeon either withdrew the electrode ~1 mm or rotated in the anti-modiolar direction until the ECochG response had recovered and the insertion process was either finished or continued. Otherwise, the insertion proceeded until the white reference marker was at the level of the RW.

Imaging and Electrode Location:

The electrode position was further interrogated in select patients with postoperative computed tomography (CT) scans and 3D reconstructions as previously reported by Skinner et al.^29,30 The insertion depth, angle of insertion, number of electrodes within each scala, and insertion angle at crossover if present were determined. The wrapping factor was calculated for arrays without any evidence of translocation; this is a measure used to compare the tightness of the wrap of an array with the modiolus. Previous studies have reported lateral wall electrodes to have a wrapping factor ~82%.³¹

Audiologic Outcomes:

Pre- and postoperative audiograms were administered to document the impact of electrode insertion on native acoustic hearing at 1-month and 3-months postoperatively. HP was defined as low-frequency pure tone average (LFPTA; 125, 250, 500 Hz) ≤ 80 dB HL, which is based on the recent AAO-HNS guidelines.³² Speech perception testing was presented at 60 dB in the CI-alone condition in the soundfield (0-degree azimuth) at candidacy and at 3 months of listening experience using CNC word test, AzBio in Quiet, and AzBio +10 dB SNR as previously described.^33,34

Statistics:

Descriptive results are presented giving mean values for pre- and postoperative hearing thresholds and insertion depth. Non-parametric testing was performed to compare HP outcomes with and without RT-ECochG. Statistical analysis was performed in IBM SPSS Statistics for Windows, Version 27.0 (IBM Corp., Armonk, NY) with significance defined as α < 0.05.

RESULTS:

Demographics:

Of the 42 patients implanted, 59.5% (28/38) were male and the median age was 78.6 years old (range, 28 – 96). Five patients had sequential bilateral CIs. No intraoperative or postoperative complications were reported (Table 1).

SLWE Positioning Outcomes and Characteristics

No tip rollovers were identified on intraoperative x-rays or postoperative CT scans. Prior to utilizing RT-ECochG, 30 patients underwent full insertion to the labeled white marker. Twelve patients underwent implantation with RT-ECochG feedback; 6 had full insertion and 6 had 1 – 3 electrodes left outside of the cochlea based on RT-ECochG feedback.

Eleven of the 12 patients where RT-ECochG was utilized underwent postoperative CT scans (Supplemental Table 1). The overall mean apical insertion depth was 315.3 ± 46.5° (range, 261° to 391°). Overall mean wrapping factor was 85.0 ± 2.3%, with no difference between full and partial insertions. The mean apical insertion angle was greater for the full insertions compared to the partial insertions (349.8 ± 24.7° vs 274.0 ± 13.3°). Postoperative CT scans confirmed that when RT-ECochG was used, all arrays were positioned in scala tympani along their entire length.

Hearing Preservation:

Pre- and postoperative audiometric results are presented in Table 2. Preoperative pure tone thresholds for all 42 patients are shown in Supplemental Figure 1. The preoperative acoustic hearing was similar across patients with and without RT-ECochG (44.5 ± 13.9 dB HL vs 43.7 ± 19.1 dB HL). Prior to RT-ECochG feedback, all implanting surgeons performed complete insertions using previously described soft surgical techniques.^35–37 Of the 30 patients where RT-ECochG was not utilized, the 1-month and 3-months mean LFPTA shifts were 45.7 ± 21.8 and 57.5 ± 25.6, respectively. In this cohort, 16 of the 30 patients (53.3%) had HP (LFPTA ≤ 80 dB HL) at 1-month and 7 patients (23.3%) had HP at 3-months postactivation.

TABLE 2:

Low-frequency thresholds and low-frequency pure tone average (LFPTA) for patients implanted with slim lateral wall electrode. Twenty-nine patients underwent insertion without real-time electrocochleography (RT-ECochG), and 12 patients underwent insertion with RT-ECochG.

	Frequency Threshold (dB HL)
	125 Hz		250 Hz		500 Hz		LFPTA
	No RT-ECochG	RT-ECochG	No RT-ECochG	RT-ECochG	No RT-ECochG	RT-ECochG	No RT-ECochG	RT-ECochG
Preop	36.1 ± 36.9	40.5 ± 16.2	44.6 ± 19.1	44.2 ± 18.3	49.8 ± 19.8	53.8 ± 13.0	43.7 ± 19.1	44.5 ± 13.9
1-month Postop	81.0 ± 32.3	51.7 ± 19.1	86.7 ± 27.9	59.2 ± 22.5	92.7 ± 25.9	73.8 ± 18.5	86.8 ± 27.8	61.5 ± 16.8
Change in HL from Preop to 1-month	46.8 ± 39.1	10.5 ± 9.3	43.8 ± 21.4	15.0 ± 10.2	44.4 ± 21.4	20.0 ± 11.3	45.7 ± 21.8	15.1 ± 7.1
3-month Postop	91.4 ± 33.0	52.2 ± 15.0	97.4 ± 28.5	66.5 ± 22.9	101.3 ± 25.4	72.8 ± 24.8	97.9 ± 27.8	66.7 ± 20.9
Change in HL from Preop to 3-month Postop	58.1 ± 43.8	10.0 ± 8.0	55.2 ± 24.6	20.0 ± 11.8	52.8 ± 21.9	22.2 ± 17.7	57.5 ± 25.6	18.9 ± 11.7

RT-ECochG was used to guide insertion for 12 patients. The mean preoperative LFPTA was 46.5 ± 16.0 dB HL and the 1-month postoperative mean LFPTA was 62.6 ± 19.0 dB HL, with a mean LFPTA shift of 16.1 ± 7.4 dB HL. The LFPTA shift was significantly less using RT-ECochG feedback to guide the depth of insertion versus those unguided cases with full insertion, with a mean difference between LFPTA threshold shift at 1-month and 3-months postactivation of 30.6 dB HL (95% CI, 20.8 – 40.3) and 38.6 dB HL (95% CI, 25.6 – 51.67), respectively. Threshold shifts across individual frequencies at 1- and 3-months postactivation are shown in Figure 2 and Supplemental Figure 2. There was no correlation between LFPTA shift at 3-months and cochlear duct length, insertion angle, or insertion depth.

FIGURE 2:

Low-frequency hearing preservation results for 1-month post-implantation of the new slim lateral wall electrode for (A) 125 Hz, (B) 250 Hz, (C) 500 Hz with and without real-time electrocochleography (RT-ECochG).

RT-ECochG Feedback and Intraoperative Findings:

Intracochlear RT-ECochG response patterns observed in all 12 cases are shown in Figure 3. Median insertion time using RT-ECochG was 112.0 seconds (range, 95.2 – 508.8). Acoustic stimulation was presented at 250 Hz in 9 patients and 500 Hz in 3 patients based on the larger ECochG response from the RW recording. There was no correlation with hearing preservation and the stimulation frequency. In eleven of the twelve cases where RT-ECochG was used, there was a rise in amplitude of ECochG response with insertion of the electrode, which was consistent with a type A pattern²² (Figure 3). There were drops in the amplitude of the ECochG response in nearly every case that required adjustments by the surgeon for ECochG response recovery. This entailed withdrawing the electrode up to 4 mm and twisting the electrode in the anti-modiolar direction 5 – 15° with respect to the initial insertion orientation of the electrode wing. For one case, there was a drop in response without recovery using these adjustments; the pattern was consistent with a type C pattern²² (Figure 3; Subject 8). The decision was made to leave 3 electrodes outside of the cochlea because attempts at full insertion led to consistent drops in RT-ECochG amplitude (> 5 μV). The LFPTA threshold shift for this patient at 1-month postop was 26.7 dB. This represented the largest shift in the cohort where RT-ECochG was utilized for active feedback and was the only patient where hearing was not preserved at 1-month.

FIGURE 3:

Real-time electrocochleography (RT-ECochG) responses of 12 subjects including intraoperative surgical adjustments are presented at a continuous acoustic stimulation frequency (250 or 500 Hz). Three-months postactivation low-frequency pure tone average shift is also shown with each tracing.

Speech-perception Performance:

For the patients where RT-ECochG was not used, average preoperative CNC, AzBio in Quiet, and AzBio +10 dB SNR in the implanted ear were 22.8%, 25.1%, and 10.5%, respectively (Table 3). At 3-months postactivation, in the implanted ear, mean CI-only CNC, AzBio in Quiet, and AzBio +10 dB SNR scores increased to 38.9%, 48.6%, and 30.1%, respectively. The mean change in CNC, AzBio in Quiet, and AzBio +10 dB SNR were 16.5% (95% CI, 5.0 – 28.0), 25.5% (95% CI, 12.4 – 38.5), and 20.3 (95% CI, 4.5 – 36.0), respectively. In the patients where RT-ECochG was utilized, average preoperative CNC, AzBio in Quiet, and AzBio +10 dB SNR were 14.0%, 28.2%, and 9.6%. For the RT-ECochG patient cohort at 3-months postactivation, mean CI-only CNC, AzBio in Quiet, and AzBio +10 dB SNR increased to 52.8%, 63.0%, and 31.4%, respectively. The mean change in CNC and AzBio in Quiet for the RT-ECochG cohort was 37.2% (95% CI, 23.0 – 51.4) and 32.5% (95% CI, 13.9 – 51.1), respectively.

TABLE 3:

CNC and AzBio speech perception test results both in cochlear implant only and bimodal condition (cochlear implant with hearing aid in contralateral ear).

	No RT-ECochG		RT-ECochG
	Preop	3 Months	Preop	3 Months
CI Only
CNC	22.8 ± 18.3	38.9 ± 18.3	14.0 ± 11.8	52.8 ± 11.0
AzBio in Quiet	25.1 ± 19.8	48.6 ± 28.2	28.2 ± 14.4	63.0 ± 23.3
AzBio in Noise (+10 dB SNR)	10.5 ± 11.3	30.1 ± 21.2	9.6 ± 8.7	31.4 ± 22.9
Bimodal (CI + HA in contralateral ear)
AzBio in Quiet	32.4 ± 18.0	63.1 ± 24.1	24.2 ± 34.6	82.0 ± 17.8
AzBio in Noise +10 dB SNR	18.4 ± 22.6	52.3 ± 25.0	20.9 ± 16.3	59.7 ± 25.6

DISCUSSION:

The purpose of this study was to describe initial HP outcomes with a new SLWE. Based on the results of 42 patients implanted with the new SLWE, HP is unpredictable and inconsistent with full insertion, without any type of electrode insertion feedback. Despite the unpredictable HP outcomes, the intraoperative experience was generally positive as all insertions proceeded with minimal resistance. Without reliable feedback, it may be difficult for CI surgeons to adapt their techniques to minimize cochlear trauma and maximize residual hearing. Early findings in this study suggest RT-ECochG may be necessary to achieve consistent HP outcomes with the SLWE.

Without RT-ECochG (n = 30), the mean LFPTA threshold shift at 3-months postop was 57.5 ± 25.6 dB HL, which was similar across 125, 250 and 500 Hz. Conversely, when using RT-ECochG feedback during insertion (n = 12), a significantly smaller LFPTA shift of 18.9 ± 11.7 dB HL shift was observed at 3-months postoperatively. RT-ECochG was not available as an intraoperative tool to monitor CI insertion for the first 30 patients, which provided a unique opportunity to compare outcomes with and without RT-ECochG. To our knowledge, no studies have directly compared HP outcomes using a single electrode with and without RT-ECochG feedback. While the findings in this study are preliminary, they strongly support the use of RT-ECochG during insertion with the new SLWE to provide feedback to maximize HP outcomes and minimize insertion trauma.

There is controversy in the literature surrounding the utility of ECochG and its ability to provide adequate feedback as a HP tool. Recent work by Lenarz et al has suggested that ECochG can reliably be used as a HP tool for the HiFocus SlimJ electrode (Advanced Bionics, Valencia, USA).²⁴ Similar to this study, ECochG was used during all insertions to determine the appropriate depth of insertion with the goal of minimizing intracochlear trauma. The SlimJ LWE has many similar characteristics to the Slim 20 LWE, measuring 20 mm in length with 16 electrodes. They reported a mean LFPTA shift around 15 dB HL, which is similar to the results observed in this study using the new SLWE (mean LFPTA shift 15.1 ± 7.1 dB HL). ECochG feedback was used in a similar manner in this study to determine the ideal insertion depth. However, definitive conclusions on the utility of ECochG during implantation for the SlimJ electrode are limited because no insertions were performed without ECochG.²⁴ A second study by Ramos-Macias et al used intraoperative ECochG for HP with both lateral wall and slim perimodiolar electrodes. They reported HP was inconsistent and unpredictable across both electrodes using RT-ECochG feedback.²⁶ Conclusions on ECochG utility intraoperatively for HP are limited by the absence of a control group, in which full insertion is achieved without ECochG feedback.

Definitive conclusions on RT-ECochG as a HP tool are also limited because of the heterogeneity in protocols throughout the literature and across institutions.^25–27 In an attempt to minimize heterogeneity between implant surgeons, a uniform protocol was prospectively created for the current study. Adjustments during implantation may include pausing insertion, withdrawing the electrode, or adjusting the insertion vector by twisting the electrode in an anti-modiolar direction, all with the goal of adjusting the electrode away from the basilar membrane. Secondly, given the hypothesis that loss of residual hearing may be a result of over-insertion due to variable cochlear duct length, consensus in the current study was to insert 17 of the 22 electrodes, and the final 5 electrodes were at the surgeon’s discretion based on RT-ECochG feedback. A uniform and strict protocol for integrating feedback during the insertion is important for consistent and reliable HP.

With a full electrode insertion and no RT-ECochG feedback, the new SLWE demonstrated a significantly worse LFPTA average shift at 3-months postoperatively when compared to other recent slim perimodiolar electrodes and lateral wall electrodes.^38–40 Our prior experience with the slim perimodiolar electrode (CI532/CI632)⁴¹ shows a LFPTA threshold shift of 19.5 ± 12.3 dB HL at 3-months postoperatively with a HP rate of 61.1% (as compared to a 57.5 ± 25.6 dB HL threshold shift and HP rate of 23.3% with the SLWE without active feedback). The experience in this study suggests that, without RT-ECochG, rates of hearing preservation are worse, as well as LFPTA threshold shifts, and speech-perception performance. By implementing RT-ECochG to guide insertion with the SLWE, we were able to achieve more reliable HP outcomes. For reference, the SLWE, slim perimodiolar electrode, and lateral wall electrode (CI522/CI622) have tip to marker lengths of 20, 14.4, and 20 mm, respectively; and distal electrode cross-sectional areas of 0.25 × 0.35, 0.35 × 0.4, and 0.3 × 0.3 mm, respectively.

In reporting early speech-perception measures for the CI-only condition, all patients significantly improved at 3-months postoperatively as compared with preimplantation. There was a slight advantage in mean CNC scores at 3-months when using RT-ECochG (38.9% vs 52.8%), which was statistically significant. These patients were tested in the CI-only condition without acoustic stimulation; thus, the difference in speech-perception performance may be greater between the two cohorts if the patients were tested in the hybrid condition. Future studies must determine whether HP impacts long-term speech-perception performance and if electroacoustic stimulation results in improved speech-perception performance using the SLWE.

This study has several notable limitations. First, there were a small number of patients that underwent CI with RT-ECochG, which limits the generalizability of the results. The preoperative audiogram for the patients who underwent implantation with the SLWE with and without RT-ECochG were similar in distribution (43.7 ± 19.1 vs 44.5 ± 13.9 dB HL). Despite the smaller sample size, the LFPTA threshold shift at 3-months was more predictable and demonstrated less variance in the RT-ECochG patient cohort (with RT-ECochG: 18.9 ± 11.7 vs without RT-ECochG: 57.5 ± 25.6). This supports the notion that RT-ECochG may have a powerful role in predicting and improving HP outcomes with the SLWE. As a result of these preliminary findings, we have integrated RT-ECochG for all SLWE implants. Secondly, only short-term audiologic outcomes and behavioral audiograms were evaluated in this study. Prior studies have shown that HP may decline overtime (at 6 or 12 months) following CI.^42,43 Future studies will need to evaluate the long-term HP results using the new SLWE. An important confounding variable that was difficult to account for in this study was the insertion time when RT-ECochG was and was not utilized. The insertion was longer when RT-ECochG was used as the surgeon was actively responding to feedback. However, much of these adjustments were made for the last 3–5 electrodes that were inserted as the largest drops in response were near the end of insertion, with the goal maximizing the final ECochG response. Most of the electrode was inserted at 30 – 40 mm/min with and without RT-ECochG, and there was no significant difference for insertion times among implanting surgeons. Further investigation is needed to determine whether the insertion time is a confounding variable.

CONCLUSIONS:

This study reports the first clinical experience with the SLWE and HP results with and without RT-ECochG feedback. Use of RT-ECochG monitoring during SLWE placement may result in fewer full electrode insertions, but significantly better HP rates and improved speech-perception performance when compared to unmonitored insertions. While these results are preliminary, they strongly suggest that that some type of monitoring and feedback is required to maximize HP results and cochlear coverage with the new SLWE. Further investigation is needed to evaluate long-term HP outcomes and to better understand the relationships among ECochG, cochlear trauma, functional outcomes, and HP.