On the relations between the excitation fronts propagating in the heart and the equivalent dipoles

The equivalent dipoles of cardiac electrical activity are determined either by minimizing the square deviation between the measured potential distribution and that generated by the dipoles or by comparing them through their multiple expansion coefficients. The two methods, called the direct and indirect method, respectively, are applied to the potential distribution obtained from a three-dimensional heart model composed of about 50000 unit cells, and the dipole locations thus obtained are compared to the mean location of the excitation fronts. When there is a single excitation front with simple shape, the equivalent dipole location obtained from the single-moving-dipole approximation coincides with the mean location of the excitation front. The coincidence is better with the direct method, but it needs longer calculation time than with the indirect method. For 25-30 ms after the onset of the ventricular depolarization, the excitation fronts have complicated shapes, and the deviations of the equivalent dipole locations from their mean locations become large even if the two-moving-dipole approximation is used.