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. Muscle Nerve, 2006