Linear Electrode Arrays for Stimulation and Recording Within Cardiac Tissue Space Constants

In this paper, we document a fabrication process that yields linear arrays of rectangular platinum black electrodes spaced 25 mum apart with edge-to-edge separation of 20 mum. The spatial arrangement is therefore sufficiently fine to insure stimulation and recording within cardiac tissue space constants, as six electrodes with dimensions of either, 5x100 mum^2, 5x250 mum² or 5x500 mum² were positioned in a 130-mum span in the arrays. Despite the small electrode sizes and available surface areas, favorable impedance characteristics were identifed. Averages ranged from 111 kOmega to 146 kOmega at 0.5 Hz and from 14 kOmega to 39 kOmega at 500 Hz. Differences in impedances between the electrode sizes tested were small. Potential differences (deltaPhis) recorded using the two central electrodes during stimulation with combinations at separations of only 75 mum , 100 mum , and 125 mum had low signal noise. As a preliminary test of the use of these arrays for possible application to impedance measurements in cardiac tissue, the deltaPhis recorded during stimulation were compared to deltaPhis obtained from finite-difference simulations using an isotropic volume conductor model. Anticipated decays in with widening electrode separation identified in those simulations matched the decays in the recorded s closely. These findings are significant because they suggest intracellular and interstitial microimpedance mesurements in heart experiments will be straightforward.