Cardiac Tissue

The Bidomain Model:

At each point of the cardiac domain there are two comingled regions, the extracellular and the intracellular domains with potentials $\phi_e$ and $\phi_i$, and transmembrane potential

$$\phi = \phi_i - \phi_e.$$

These potentials drive currents,

$$i_e = - \sigma_e\nabla\phi_e, \qquad i_i = - \sigma_i\nabla\phi_i\nonumber$$

where $\sigma_i$ and $\sigma_e$ are conductivity tensors.

Total current is

$$i_T = i_e + i_i = - \sigma_e\nabla\phi_e - \sigma_i\nabla\phi_i.$$