Characteristics of malfunctioning channels in pediatric cochlear implants

Abstract

Objectives/hypothesis: To examine the characteristics of pediatric cochlear implant channel malfunction preceding device failure.

Study design: : Retrospective review.

Methods: All pediatric patients who underwent cochlear implantation at a tertiary academic medical center were reviewed regarding device type, reason for replacement, time to replacement, and timing and pattern of channel faults in failed versus nonfailed devices.

Results: Between 1993 and 2008, 264 pediatric cochlear implantations were performed. With an average 894-day follow-up, the replacement rate was 9.5% (25/264). Reasons for replacement were device failure (6.4%), medical/surgical failure (2.3%), and obsolescence (0.8%). Replacement rates were comparable among Advanced Bionics (13.3%), Cochlear Corporation (6.3%), and MED-EL (10.3%) devices. Fifty-two cochlear implants developed at least one channel fault, and 13 eventually progressed to failure requiring replacement. MED-EL devices comprised 12 of these 13 failures. At the 12-month follow-up interval, one, three, and five channel faults predicted 40%, 75%, and 100% probabilities of eventual electrode failure, respectively. Channels destined to fail demonstrated small, yet statistically significant, impedance elevations 12 months before failure and large elevations 3 months before failure.

Conclusions: Replacement of cochlear implants in pediatric patients is common and is due to device malfunction about one half of the time. Earlier initial channel fault, earlier subsequent channel faults, adjacent channel faults, and a greater total number of channel faults were associated with the need for replacement surgery. Elevations in a channel's impedance should raise the concern for an impending failure. These predictors can help the cochlear implant team when considering surgery to replace the device.

Fig. 1

(a) Time to cochlear implant replacement stratified by reason for failure in all manufacturers combined (left), and by manufacturer for device failures only (right). *Versus nondevice failures; P <.03. **Versus MED-EL device failures only; P = .004. (b) Distribution of failed channels in Cochlear Corporation and MED-EL devices (all devices are included, not just those requiring replacement).

Fig. 2

(a) Profile of consecutive and simultaneous channel failures in failed electrodes. The top of the black bar shows the chance of each channel failure occurring. The top of the white bar shows the chance that each channel failure will occur simultaneously with the first channel failure. (b) Profile of consecutive and simultaneous channel failures in functioning electrodes. (c) Time course of consecutive channel failures in failed versus nonfailed electrodes. The dotted line marks 1 year. *Versus failed electrodes; P = .03. **Versus failed electrodes; P =.02. ***Versus failed electrodes; P =.05.

Fig. 3

Chances and odds ratios of electrode failure stratified by number, timing, and patterns of channel failures.

Fig. 4

Time course of impedance values of failed channels versus normal channels prior to channel fault. *Versus normal channels; P <.001.