Quantitative Formulations of Electrophysiological Sources of Potential Fields in Volume Conductors

The noninvasive measurement of electrical potentials at the surface of the body (e.g., the electrocardiogram) has long been considered an important tool in clinical diagnosis. Electrophysiological modeling and simulation is valuable as an aid in the interpretation of such potential recordings. In all cases, the potential field can be considered to arise from bioelectric sources operating in a volume conductor. This paper concentrates on the appropriate quantitative formulation for these sources. Such sources arise from excitable cells undergoing action potentials (primary sources) or at passive boundaries between regions of different conductivity (secondary sources). These sources are described and discussed for arbitrary cell shapes, circular cylindrical cells, conductive media with piecewise constant conductivity, and for syncytial tissue whose macroscopic properties are anisotropic.