Multidimensional activation of the heart: The effect of anisotropy in conductivity of cardiac tissue

Abstract

This paper examines the current flow patterns and excitation isochrones of a two-dimensional cardiac tissue with anisotropic intracellular and interstitial conductivity parameters. Only when the anisotrophy ratios in intracellular and interstitial space are equal does the behavior of current flow extrapolate from one dimensional cable theory. For realistic (measured) conductivities a component of action current flow is characterized by wide loops and multiple membrane crossings. Furthermore the transmembrane current at any site depend on transmembrane potential in the entire surrounding region. Isochrone simulation based on Hodgkin-Huxley rising phase shows that the assumption of local plane wave behavior is not generally acceptable. This is not surprising in view of the current flow patterns which do not correspond to simple one-dimensional flow, locally. The consequences of this study is that simulation of activation in real cardiac tissue must recognize the effects of anisotropy. The implications could be important not only for normal activation patterns but for studies of arrhythmias as well.