Propagated insertional activity: a model of positive sharp wave generation

In this study we utilized a dual monopolar needle recording technique to assess propagated electromyographic insertional activity from the same single muscle fiber in order to characterize different categories of insertional activity. A total of six combinations of insertional activity were identified. Only two fundamental types of single muscle-fiber insertional discharge configurations were generated: biphasic initially-negative and monophasic positive. The propagated waveforms corresponding to these two insertional discharges were primarily triphasic initially-positive and, only rarely, monophasic positive. The monophasic positive insertional activity generated at the inserting electrode site is postulated to arise from a depolarization zone adjacent to a needle-induced peri-electrode membrane crush. The monophasic positive discharge was utilized as a model for positive sharp wave generation. It is postulated that the majority of positive sharp waves are initiated at the inserting electrode adjacent to a needle-induced zone of muscle membrane crush in contrast to the previous supposition that positive sharp waves are blocked fibrillation potentials.