BIPOLAR STIMULATION OF A 3-DIMENSIONAL BIDOMAIN INCORPORATING ROTATIONAL ANISOTROPY

A bidomain model of cardiac tissue was used to examine the effect of t ransmural fiber rotation during bipolar stimulation in three-dimension al (3-D) myocardium. A 3-D tissue block with unequal anisotropy and tw o types of fiber rotation (none and moderate) was stimulated along and across fibers via bipolar electrodes on the epicardial surface, and t he resulting steady-state interstitial (Phi(e)) and transmembrane (V-m ) potentials were computed. Results demonstrate that the presence of r otated fibers does not change the amount of tissue polarized by the po int surface stimuli, but does cause changes in the orientation of Phi( e) and V-m in the depth of the tissue, away from the epicardium. Furth er analysis revealed a relationship between the Laplacian of Phi(e), r egions of virtual electrodes, and fiber orientation that was dependent upon adequacy of spatial sampling and the interstitial anisotropy. Th ese findings help to understand the role of fiber architecture during extracellular stimulation of cardiac muscle.