POTENTIAL DISTRIBUTIONS GENERATED BY POINT STIMULATION IN A MYOCARDIAL VOLUME - SIMULATION STUDIES IN A MODEL OF ANISOTROPIC VENTRICULAR MUSCLE

Introduction: We present simulations of extracellular potential patter ns elicited by delivering ectopic stimuli to a parallelepipedal slab o f ventricular tissue represented as an anisotropic bidomain incorporat ing epi-endocardial fiber rotation. Methods and Results: Simulations w ere based on an eikonal model that determines wave-front shapes throug hout the slab at every time instant during the depolarization phase, c oupled with an approximate model of the action potential profile. The endocardial face of the slab was in contact with blood and the composi te volume was surrounded by an insulating medium. The effect of a simp lified Purkinje network was also studied. Results: (1) For all pacing depths, except endocardial pacing, a central negative area and two pot ential maxima were observed at QRS onset in all intramural planes para llel to the epicardium. In all planes, the axis joining the two maxima was approximately aligned with the direction of fibers in the plane o f pacing. Endocardial pacing generated a different pattern, but only w hen blood was present; (2) During later stages of excitation, outflowi ng currents (from the wavefront toward the resting tissue) were always emitted, at all intramural depths, only from those portions of the wa vefront that spread along fibers. At any given instant, the position o f the two potential maxima in a series of planes parallel to the epica rdium and intersecting the wavefront rotated as a function of depth, f ollowing the rotating direction of intramural fibers. Purkinje involve ment modified the above patterns. Conclusion: Epicardial and endocardi al potential maps provided information on pacing site and depth and on subsequent intramural propagation by reflecting the clockwise or coun ter-clockwise rotation of the deep positivity. Results may be applicab le to epicardial and endocardial potential maps recorded at surgery or from endocavitary probes.