Relating Epicardial to Body Surface Potential Distributions by Means of Transfer Coefficients Based on Geometry Measurements

Although it has been known throughout this century that a complex sequence of electrical events is produced on the body surface by the electrophysiological properties of the heart, the question of how well these body surface events can be explained mathematically on the basis of experimental measurements of cardiac geometry and electrical activity remains unanswered. Recent advances in experimental capabilities have made possible the near simultaneous measurement of both cardiac epicardial and corresponding body surface potential distributions from in vivo animal preparations using chronically implanted electrodes to keep the volume conductor intact. This report provides a method for finding transfer coefficients that relate the epicardial and body surface potential distributions to each other. The method is based on knowing the geometric location of each electrode, and on having enough electrodes to establish the geometric shape and the potential distribution of closed epicardial and body surfaces. However, the method does not require that either the heart or body surfaces have any special shape, such as that of a sphere, or that any electrical quantities, such as voltage gradients, be known in addition to the potentials. The use of potential distributions to represent heart electrical activity is advantageous since such distributions can be directly measured experimentally, without a transformation to any other form, such as multiple current-generating dipoles, being required. This report includes a statement of the underlying integral equations, the procedure. for finding the equations' coefficients from geometry measurements, some considerations for computer algorithms, and an example.