  The heart beats due to the synchronized contraction of cardiomyocytes
triggered by a periodic sequence of electrical signals called action
potentials, which originate in the sinoatrial node and spread through the
heart's electrical system. A large body of work is devoted to modeling the
propagation of the action potential and to reproducing reliably its shape and
duration. Connection of computational modeling of cells to macroscopic
phenomenological curves such as the electrocardiogram has been also intense,
due to its clinical importancce in analyzing cardiovascular diseases. In this
work we simulate the dynamics of action potential propagation using the
three-variable Fenton-Karma model that can account for both normal and damaged
cells through spatially inhomogeneous voltage diffusion coefficient. We monitor
the action potential propagation in the cardiac tissue and calculate the
pseudo-electrocardiogram that reproduces the R and T waves. The R wave
amplitude varies according to a double exponential law as a function of the
(spatially homogeneous, for an isotropic tissue) diffusion coefficient. The
addition of spatial inhomogeneity in the diffusion coefficient by means of a
defected region representing damaged cardiac cells, may result in T-wave
inversion in the calculated pseudo-electrocardiogram. The transition from
positive to negative polarity of the T-wave is analyzed as a function of the
length and the depth of the defected region.
