The effect of interelectrode distances on measurements of the local potential gradient of the propagating cardiac excitation at a microscopic size scale

Cardiac excitation spread at a microscopic (<200 μm) size scale can be seen as a propagating signal in a discrete electrical network with stochastically distributed electrical discontinuities at the sites of cell to cell connections. In order to test the hypothesis if this discontinuous spatio-temporal process can also be detected as discontinuous distribution of extracellular potentials the authors developed high-resolution sensor arrays in thin-film technique (180 μm to 20 μm interelectrode spacing) as well as array amplifiers and data acquisition systems. The time course of signals from bipolar recordings (gradients) and from quadrupolar recordings (field magnitude) was compared for different interelectrode distances. All signals were be taken from a set of 25 signals obtained simultaneously by one array recording. The measurements showed that from 280 μm down to the smallest possible interelectrode distance of 20 μm the measured the gradient of the local potential increased by a factor of two. This local field parameter varied substantially within an area of 200×200 μm²