The volume conductor effects of anisotropic muscle on body surface potentials using an eccentric spheres model

Anisotropy for both the myocardium and the skeletal muscle is explicitly incorporated into the eccentric spheres volume conductor model. The anisotropy is treated as having uniform orthogonal components in the radial and tangential directions for both the skeletal muscle and myocardium. The solution for Laplace´s equation is written in a series expansion of appropriate basis functions for each region. In the isotropic regions spherical harmonics with integer radial dependence and Legendre polynomial azimuthal dependence are utilized. Two basic conclusions are drawn from the results. First, the treatment of skeletal muscle anisotropy by the boundary extension method is a valid and useful simplification which yields errors of 2% for the peak body surface potential. Secondly, myocardial anisotropy has a significant effect on the magnitude of body surface potentials. It is demonstrated that the peak body surface potential is attenuated by as much as 14% for a 3 to 1 ratio of the tangential to radial conductivity compared to an isotropic assumption.