Moving Dipole Inverse ECG and EEG Solutions

This paper reviews and updates the single moving dipole (SMD) and two moving dipole (TMD) inverse electrocardiographic and electroencephalographic solutions. These inverse solutions are particularly appropriate when the electrical activity of the heart or brain may be represented by one or two well-localized foci. They attempt to match the measured body surface or evoked scalp potentials to potentials generated on the surface of a model of the intervening volume conductor by one or two moving current dipoles, respectively. The two alternative methods of solution are discussed initially. The first is a direct least-squares error match of measured and model-generated surface potentials, the second an indirect solution based on the least-squares error match of the potentials due to equivalent multipole series representations of the real and model sources, respectively. Next, brief reviews of moving dipole inverse solutions in the EEG and ECG fields are presented. Simulation studies, as well as experimental and clinical studies in animals and humans, are described. The Discussion section summarizes the optimum solution approaches that should be used in clinical EEG and ECG studies in man. It also cautions against the temptation to translate the numerical adequacy of inverse SMD and TMD solutions into physiological validity, without independent knowledge as to the nature of the underlying sources.