Studies of the Equivalent Cardiac Generator Behavior of Isolated Turtle Hearts

Abstract

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 6CWP; 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.

Detection and localization of multiple epicardial electrical generators by a two-dipole ranging technique.

“…The hearts were rapidly excised through a left thoracotomy and the cut ends of the aortic roots were tied to an electrically insulated perfusion cannula. This cannula passed vertically through one hemisphere of a previously described 10 …”

“…10 Stability of the waveforms recorded during the 18-second data acquisition period was verified by an autocorrelation technique. Precision of the instrumentation system and, particularly, the accuracy of preamplifier calibration was checked by computing "closure error," a scalar directly proportional to the degree by which the sum of potentials recorded from leads forming a closed Kirchoff s loop deviated from the expected zero value.…”

“…The 24 parameters of a centric multipole series through the hexadecapole term were calculated as previously described. 8 ' 10 Three location and three moment terms of the single moving dipole that best reproduced the 32 electrode potentials were computed by an iterative procedure developed by Terry et al 9 Thirty-two equations were constructed of the form…”

“…Reports from this laboratory with regard to turtle 10 and rabbit 17 hearts are representative. When relative dipolarity was assessed by inverse computation of the parameters of a single moving dipole, an average of 30% of root mean square (RMS) surface potential during the middle third of the QRS was nondipolar.…”

“…Electrocardiographic signals were simultaneously recorded from 32 silver-silver chloride electrodes on the inner surface of the sphere, paired to form 32 bipolar leads comprising a closed Kirchoff's loop. 10 - 12 Electrodes were placed at the 20 vertices and at the centroids of the 12 facets of an underlying regular icosahedral reference figure. Signals were amplified by low noise (4 /j.V, peak-topeak) differential amplifiers which were calibrated under computer control (PDP-7).…”