Dipole moment of in vivo and isolated perfused rabbit hearts

We have measured magnitude and location of heart dipole moment during QRS in 46 New Zealand white rabbits. The spatial magnitude curve had one to three peaks. Mean values were M1 = 80 +/- 10 microA-cm (N = 5) pointing to right anterior and caudal, M2 = 260 +/- 15 microA-cm (N = 42) directed slightly to left of due anterior and caudal, and M3 = 236 +/- 9 microA-cm (N = 43) pointing towards left posterior and cephalad. The mean thorax resistivity was 250 ohm-cm. For 23 rabbits, M2/M3 greater than 1 and for 16 rabbits, M2/M3 less than 1. Mean times of occurrence of the three peaks were 5.8, 11.2, and 19.6 ms, respectively. Spatial magnitude curves for hearts perfused at the center of a sphere showed usually one major peak at about 19 ms. Locuscardiograms of in vivo hearts were also measured. By comparing M values for in vivo and isolated hearts, we found that M1 values agreed closely but mean M2 measured from the hearts in vivo was 2.5 times that for the isolated hearts, and M3 for in vivo hearts was about two-thirds that for isolated hearts. We relate these differences to the effects of intracardiac blood and lungs on the measured dipole moment.