THE INDUCTION OF REENTRY IN CARDIAC TISSUE - THE MISSING LINK - HOW ELECTRIC-FIELDS ALTER TRANSMEMBRANE POTENTIAL

This review examines the initiation of reentry in cardiac muscle by st rong electric shocks. Specifically, it concentrates on the mechanisms by which electric shocks change the transmembrane potential of the car diac membrane and create the physiological substrate required by the c ritical point theory for the initiation of rotors. The mechanisms exam ined include (1) direct polarization of the tissue by the stimulating current, as described by the one-dimensional cable model and its two- and three-dimensional extensions, (2) the presence of virtual anodes a nd cathodes, as described by the bidomain model with unequal anisotrop y ratios of the intra-and extracellular spaces, (3) polarization of th e tissue due to changing orientation of cardiac fibers, and (4) polari zation of individual cells or groups of cells by the electric field (' 'sawtooth potential''). The importance of these mechanisms in the init iation of reentry is examined in two case studies: the induction of ro tors using successive stimulation with a unipolar electrode, and the i nduction of rotors using cross-field stimulation. These cases reveal t hat the mechanism by which a unipolar stimulation induces arrhythmias can be explained in the framework of the bidomain model with unequal a nisotropy ratios. In contrast, none of the examined mechanisms provide an adequate explanation for the induction of rotors by cross-field st imulation. Hence, this study emphasizes the need for further experimen tal and theoretical work directed toward explaining the mechanism of f ield stimulation. (C) 1998 American Institute of Physics.