<< 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:
  1. 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.
  2. 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.
  3. Arrythmogenesis, whenever the behavior of filaments close to the tissue-bath effect is of interest
  4. 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 model-dependent nonlinear current-voltage relationship.
The system of non-linear 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 non-linear models describing the current flow through the cell membrane, which leaves one domain to enter the other.
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