Effective epicardial resistance of rabbit ventricles

This study evaluated effective resistances on the ventricular surfaces of arterially-perfused rabbit hearts. Effective resistances were determined with a four-electrode array that was parallel or perpendicular to epicardial fibers. Resistance along or across epicardial fibers was determined by applying current to the epicardium with two parallel line electrodes and measuring potentials in the region between the electrodes. Computer simulations were performed to gain insight into the distribution of current in the ventricular wall. The effective resistances were not different along versus across fibers. Simulations showed that transmural rotation of fibers causes current to be distributed differently when the electrode is oriented perpendicular versus parallel to epicardial fibers. When the array is oriented so that epicardial current is across fibers, the fraction of current that flows transmurally and along the deeper fibers increases while the fraction of current that flows epicardially decreases. This introduces isotropy of the effective resistance. Thus, in contrast to isolated cardiac fibers, the ventricular epicardium exhibits isotropic effective resistance due to transmural rotation of fibers. The rotation and isotropic resistance may be important for cardiac electrical behavior and effects of electrical current in the ventricles.