Electrical stimulation of cardiac tissue by an electrode in a conductive bath

We calculate the transmembrane potential in a passive, three-dimensional slab of cardiac tissue during electrical stimulation. The stimulating electrode is located in an isotropic, conductive bath adjacent to the tissue. The electrode is bipolar, with its axis perpendicular to the surface of the slab. The cathode is nearest the tissue surface. The bidomain model represents the electrical properties of the tissue. The tissue is depolarized under the cathode and hyperpolarized in the direction parallel to the fibers. These results are consistent with 2- and 3-dimensional bidomain simulations without a conductive bath. Unequal anisotropy ratios are not necessary for hyperpolarization to exist near the cathode.