Influence of cardiac fiber orientation on wavefront voltage, conduction velocity, and tissue resistivity in the dog.

When the canine epicardium is stimulated, the spread of epicardial excitation is 2.4 times faster parallel to the long axes of the cardiac fibers than perpendicular to them. Likewise, gross tissue resistivity is lower parallel to fibers by a factor of 3.2, and the voltage across the depolarization wave is approximately three times as great in the longitudinal direction. Equations are presented which relate these variables. Theoretical considerations confirm the experimental finding that the potentials around a wave of depolarization cannot be accounted for by the conventional hypothesis that the wavefront is a uniform double-layer current source.