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

Several aspects of the four-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 four-electrode sensor was developed for the measurement of local myocardial resistivity in two 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.