Studies of the Equivalent Cardiac Generator Behavior of Isolated Turtle Hearts

Equivalent cardiac generator components were determined for a series of excised turtle hearts immersed in Ringer's solution. Relatively large preparations were contained within a specially designed spherical chamber, and electric field potentials were derived from 20 evenly spaced electrodes on the chamber wall. A laboratory computer was used to acquire and store the 20 leads of signal data in digitized form in real time. An eccentric dipole was optimally fitted to the surface potentials for each 2 msec sample; the remaining voltages were used to determine a centric multipolar series through octapolar content. In addition to the purely quantitative parameters which were thus determined, sequential mapping of isopotential distribution over the spherical boundary gave valuable qualitative insights into the behavior of the equivalent generator throughout ventricular depolarization. This activity varied in complexity from predominantly dipolar to strongly nondipolar among different preparations. Peak quadripolar activity ranged from a low of 10 to a high of 60%; the corresponding figures for octapole content were 5-61%. The overall technique permits experimental exploration of several theoretical principles which have been advanced since 1954. Pilot studies on rabbit hearts indicate that the method will also be applicable to mammalian hearts.