The four-electrode resistivity technique in anisotropic media: theoretical analysis and application on myocardial tissue in vivo

Several aspects of the 4-electrode resistivity technique were studied with special emphasis on the theoretical determination of penetration depth and sample volume in anisotropic media such as (cardiac) muscle. Moreover, the presence of a thin disturbing layer on top of the medium under study was analyzed. A 4-electrode sensor was developed for the measurement of local myocardial resistivity in 2 orthogonal directions. The sensor was applied to the epicardium of anesthetized open chest dogs and, as an example, results are given on the frequency dependence (5-60 kHz) and the changes during the cardiac cycle of longitudinal and transverse myocardial resistivity.