Model studies of extracellular electrograms arising from an excitation wave propagating in a thin layer

Extracellular potentials were calculated for a wave of activation propagating through a thin layer of tissue. Sources were represented on the basis of the bidomain model, with the observation point at the tissue surface. Calculated potentials were found to be insensitive to the length of the wavefront if it passed under the recording electrode provided its length exceeded 1 mm, but to decrease rapidly when the wave passed to a side of the electrode. Contributions of source regions with a lateral displacement from the electrode greater than about 0.3 mm were substantially diminished. The effects of the thickness of the layer and velocity of propagation on amplitude were investigated.