IDENTIFYING ELECTRODE FAILURES WITH COCHLEAR IMPLANT GENERATED SURFACE-POTENTIALS

A procedure for measuring surface potentials called electrode-by-elect rode (E-E) mapping is described that can detect the nonintermittent ma lfunctioning of the implanted receiver and electrode array of multicha nnel cochlear implants, such as the Cochlear (Nucleus) device. E-E map ping is based on the sequential stimulation of all paired combinations of electrodes. The recorded waveforms were averaged and all peak-to-p eak 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 pa tients whose behavioral thresholds were in agreement with hardware pro blems, including one case of overstimulation at high stimulus levels. In one patient who was suffering from overstimulation without any devi ant thresholds, no failure could be detected. The procedure takes abou t a quarter of an hour and the stimulus amplitude needed is below thre shold for most patients, which makes it especially useful in children. An informative partial E-E map can be made during implantation and re quires virtually no extra theater time.