Optical recordings of cardiac transmembrane potential around an extracellular electrode in electrically anisotropic, bullfrog atrium

The authors have studied the spatial distribution of cardiac transmembrane potential around an extracellular unipolar electrode during electrical stimulation. The recordings were obtained from the bullfrog atrium along the transverse and longitudinal fiber directions. These recordings revealed the presence of a uniformly polarized region in the transverse fiber direction. In the longitudinal fiber direction, adjacent oppositely polarized regions coexist. These results are qualitatively predicted by an activation function developed for uncoupled fibers. They contradict the predictions of conventional cable models and also support newly developed models of cardiac tissue