Experimental evaluation of the mean electrical equivalent generator of the isolated rabbit heart

Previous data have documented that the instantaneous cardiac equivalent generator is inadequately modeled as a single dipole. The properties of the mean equivalent generator during the QRS, ST-T and QRST intervals were determined in 22 isolated rabbit heart preparations suspended within a spherical volume conductor and perfused with an electrolyte solution. ECG potentials recorded from 32 surface electrodes were processed to compute instantaneous equivalent generator properties at 0.4 to 2.0 msec intervals during QRS and ST-T. QRS and ST-T areas of each electrode waveform were determined and processed to compute the parameters of the mean generator during QRS, ST-T and QRST intervals. A centric dipole fit 77.96, 71.73 and 67.48 percent of the recorded summed square (SSQ) area during these three intervals. Corresponding values for a single moving dipole model were 86.14%, 87.17% and 86.11%. A four element centric multipole series, in contrast, fit over 98% of SSQ area during each interval. Isoarea maps demonstrated multiple maxima and/or minima in 48% of the studied cases. Thus, mean cardiac forces during activation and recovery, as well as the instantaneous counterparts, are inadequately represented as single dipolar generator sources.