The difference between fibrillations and positive sharp waves is due to tissue filtering.

Abstract

Fibrillation potentials and positive sharp waves share many characteristics, and in general have the same clinical importance. Whether they are two species of the same potential or two different waveforms has been a long-standing controversy. The blocking hypothesis and inadvertent intracellular recording are two theories proposed to explain the difference between the two potentials, but neither is entirely satisfactory. In this study, waveforms with fibrillation potential configurations are modified by the standard filter settings on an electromyograph to attain positive sharp wave configurations. Single-fiber muscle action potentials were recorded at a low-frequency filter of 500 Hz and a high-frequency filter of 20 kHz, and had the appearance of a fibrillation potential. Changing the low-frequency filter and high-frequency filter to 0.2 Hz and 100 Hz respectively caused these same potentials to have a positive sharp wave configuration. Similarly, fibrillation potentials recorded from patients at a low-frequency filter and a high-frequency filter of 20 Hz and 10 kHz respectively had the appearance of positive sharp waves when the low-frequency filter and high-frequency filter were changed to 0.2 Hz and 500 Hz respectively. The authors propose that tissue filtering and the spatial relationship of the fibrillating fiber to the recording electrode determine whether the waveform will have a fibrillation potential configuration or a positive sharp wave configuration. The ability to model these waveforms artificially simply by changing the bandpass suggests that the passive electrical properties of the recording environment may suffice to explain much of the difference between fibrillation potentials and positive sharp waves.