Anatomical and microstructural factors affecting the electrical activity of the heart. Experimental findings and mathematical simulations.

We developed an experimental preparation in which we record 1500 intramural electrograms from the ventricular walls of an isolated dog heart. The heart is plunged into an electrolytic tank shaped as a human thorax. The tank carries 1300 electrodes uniformly distributed in the conducting volume and on its surface. We obtain 2800 electric signals which enable us to define the spread of excitation and the sequence of repolarization in the heart, and to map the spatial distribution of potentials and currents in the heart, in the chest and on the body surface during a heart beat. Experimental results and mathematical simulations show that excitation, repolarization, the spatial distribution of heart potentials and the shape of the electrocardiograms are dominated by a small number of anatomical factors, namely: the geometry of the ventricles, the epi-endocardial rotation of myocardial fibers orientation in the ventricular walls, the obliqueness of the fibers relative to the epicardial surface and structure of the conduction system.