The bidomain model of cardiac tissue: from microscale to macroscale
Cardiac muscle is made up of coupled myocytes, embedded in an interstitial space comprised of blood vessels, connective tissue, fibroblasts fluid, and other cell types and adjoining some extracellular fluid. The bidomain model was originally developed to describe the current flow in both these three spaces using continuous partial differential equations. The classical form assumes averaged potentials and currents and considers the intracellular and interstitial spaces to be separated by a cell membrane, defined at every point in space. Over the last 40 years, the model has been used to study stimulation through the extracellular or interstitial currents, the effect of the adjoining fluid on wavefront propagation and the basis for the extracellular potentials often recorded clinically. In this chapter, we derive the bidomain model from idealized lattice of cells coupled through gap junctions and show how the tissue conductivities and associated anisotropy relate to the underlying cellular structure. We also discuss some of the challenges to bidomain prediction that may necessitate changes to the underlying formulation to capture certain diseased states.