The Forward Problem of Electrocardiography: Theoretical Underpinnings and Applications

The forward problem of electrocardiography refers to the calculation of the potentials on the body surface due to the heart sources, using the theoretical equations of electromagnetism. As a prerequisite for this calculation, suitable representations of the heart sources and of the torso geometry are needed. The former is usually assumed to be a current dipole, which may be taken to be a current source and sink of equal magnitude I separated by a very small distance δ. The dipole is then represented as p=Iδ. The bold font indicates that p is a vector, whose magnitude is Iδ and whose direction is that of the vector δ, namely along the line joingng sink to source. The rationale behind representing the heart sources with a current dipole is taken up in Section 2.2 below. In a second approach, the question of an adequate representation of the heart sources is circumvented by calculating the torso surface potentials using the actual potentials on the heart’s epicardial surface (or more correctly on the surrounding pericardial sheath) as the starting representation. This second approach will also be described.