Dipole moment of isolated rabbit heart

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Abstract
The spatial dipole moment, M, of the isolated perfused rabbit heart at the center of a spherical container was determined during the cardiac cycle from three sets of bipolar voltage measurements. Average peak values for 12 experiments were 72,355, and 128 µa-cm for P, QRS, and T waves, respectively. Rates of change of M and spatial angle were also calculated. Successive excitation vectors are described by a sequence of numbers indicating directions in space. Comparisons between frontal plane vectors of in vivo and isolated hearts showed that, in QRS, average mean values of αf were 51° and 57°; for T these angles were 73° and –137°, indicating a reversal of direction. For P, the angles were 67° and –33°. The hypothesis is advanced that the spread of excitation in the atria is faster along the endocardial surface due to the relatively low resistivity of intracardiac blood; this results in a substantial dipole component perpendicular to the atrial wall.