Identifying electrode failures with cochlear implant generated surface potentials

A procedure for measuring surface potentials called electrode-by-electrode (E-E) mapping is described that can detect the nonintermittent malfunctioning of the implanted receiver and electrode array of multichannel cochlear implants, such as the Cochlear (Nucleus) device. E-E mapping is based on the sequential stimulation of all paired combinations of electrodes. The recorded waveforms were averaged and all peak-to-peak amplitudes were combined into one graph for a comprehensive check on open circuit or short-circuited electrodes. Normative data from 21 patients are given. E-E mapping detected electrode failure in three patients whose behavioral thresholds were in agreement with hardware problems, including one case of overstimulation at high stimulus levels. In one patient who was suffering from overstimulation without any deviant thresholds, no failure could be detected. The procedure takes about a quarter of an hour and the stimulus amplitude needed is below threshold for most patients, which makes it especially useful in children. An informative partial E-E map can be made during implantation and requires virtually no extra theater time.