


<< click on the image to enlarge! 
One of the salient features of bidmain models is their capability to
predict virtual electrode polarizations. 

The bidomain equations are, among the computationally tractable approaches,
the most complete description of the electrical behavior of cardiac
tissue. Unlike the somehow simpler monodomain equations, the bidomain
equations explicitly account for current flow in the extracellular/interstitial
domain. Depending on a particular question, the use of bidomain or equivalently
complete formulations may be mandatory:
 Unequal Anisotropy ratios between the domains: All phenomena related
to differences in anisotropy ratios between the intracellular and interstitial/extracellular
domain are not captured by monodomain approaches.
 Defibrillation: One of the main applications of the bidomain, since
most effects important for defibrillation are related to the presence
of unequal anisotropy ratios like Virtual Electrode Polarizations (VEPs),
this cannot be studied in any reasonalbe boundary way with the monodomain.
 Arrythmogenesis, whenever the behavior of filaments close to the
tissuebath effect is of interest
 Bath loading effects in general.
Like the monodomain, the bidomain can be derived from the 1D core conductor model
using a homogenization procedure. The only new concept introduced by bidomain is the
interpenetration of intracellular and interstitial domain. That is, at each single point in
space, intracelluar space, interstitial space and membrane coexist. This concept is visualized
in a simplified way for a 2D case in the following figure:




<< click on the image to enlarge! 
Bidomain representation of cardiac tissue in 2D. Intra and extracellular (interstitial)
domains are represented by the gray and orange planes respectively. Within each
domain, conductivities are anisotropic as indicated by the different resistances in each
direction. Each point in the intracellular domain has a potential associated with it, φi,
and a corresponding point in the extracellular domain with the potential φe,. The voltage
between the points is denoted Vm, and the points are linked by transmembrane current
flow, Im. Each green cylinder represents a section of membrane which is described by a
modeldependent nonlinear currentvoltage relationship. 

The
system of nonlinear partial differential equations models both the
intracellular and extracellular domains of the cardiac tissue from an
electrostatic point of view. The coupling of the two domains is performed via nonlinear
models describing the current flow through the cell membrane, which
leaves one domain to enter the other. 



