On two mechanisms of the domain structure of ventricular fibrillation

Analysis of optically recorded irregular electrical wave activity on the su rface of the heart during experimentally induced fibrillation reveals a str ong local temporal periodicity. The spatial distribution of the dominant te mporal frequencies of excitation has a domain organization. The domains are large (approximate to1 cm(2)) and they persist for minutes. We demonstrate that these data can be reproduced in a two-dimensional excitable medium go verned by the FitzHugh-Nagumo equations with a spatial inhomogeneity. We id entified two potential mechanisms that may contribute to the observed exper imental dynamics: coexistence of stable spiral waves with noncommensurate f requencies of rotation, and Wenckebach-like frequency division from a singl e spiral source due to inhomogeneity. The number of domains is not an index of the number of wave sources. Both mechanisms reproduce the uniformity of the dominant frequency within individual domains and sharp boundaries betw een domains. The possibility of distinguishing between different mechanisms using Lissajous figures is discussed.