A model study of the effects of anisotropy on the stability of cardiac reentrant activity

A two-dimensional parallel-cable sheet model of cardiac tissue, with a brick-wall arrangement of resistive transverse interconnections, was used to study the effects of tissue anisotropy on reentry. Reentrant activity was induced using a modified cross-shock protocol. A sheet with a low anisotropy ratio (<6.0) could be rescaled in the transverse direction so that the reentrant activity had the same basic characteristics as those observed in the nominal sheet. Once the anisotropy ratio passed 6.0 the similarity was lost. Reentry in the high anisotropy sheet had a longer cycle length and propagation tended to be blocked more easily, which led to wave breakup and the appearance of multiple wavefronts. These results suggest a fundamental difference between reentrant activity in low anisotropy tissue, typical of ventricular myocardium, and high anisotropy tissue typical of the atria