Re-entrant Arrhythmias and their Control
in Models of Mammalian Cardiac Tissue

We use detailed biophysical, and simplified models of excitation propagation in heart muscle to study the properties of re-entrant arrhythmias. Using a detailed model of excitation combined with a bidomain description of propagation and action of electric current, we have obtained a theoretical estimation for the defibrillation threshold consistent with experimental data. A series of properly timed low-voltage stimuli can cause directed ``resonant'' drift of this block, and act as a low-voltage defibrillation strategy. Experimentally observed activation patterns in fibrillating tissue are more complicated than the simplest spiral wave patterns. This is due to complicated geometry, three-dimensional nature of the tissue, its anisotropy and inhomogeneity. However, some fibrillation patterns can be produced by a single re-entrant wave, modulated by inhomogeneous tissue properties and Wenckebach frequency division.