Sequential change in the different of potential distribution between a normal subject and simulated torso model.

Isopotential map was obtained every 3 msec after the onset of ventricular activation from 85 unipolar lead ECGs of a normal subject (Measured map) and similar map at the corresponding instant (Simulated map) was also obtained by means of mathematical calculation under the assumption that the cardiac electromotive force can be represented by a single electric dipole fixed at the heart center. These 2 maps were quantitatively compared and difference was delineated on a map (Difference map). Although, in major aspect, there was a fairly good agreement between Measured and Simulated maps during early stages of ventricular activation, a remarkable difference of potential distribution began to appear between them around the time of occurrence of epicardial breakthrough of the ventricular activation front. From that t me on, it became impossible to represent the cardiac electromotive force into 2 or more electric dipoles in Difference map. Difference maps around the instant of epicardial breakthrough of the ventricular activation were supposed to be helpful for the estimation of the spread of ventricular activation.