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High Resolution Magnetic Images of Planar Wave Fronts Reveal Bidomain Properties of Cardiac Tissue

Jenny R. Holzer ^*, Luis E. Fong , Veniamin Y. Sidorov ^* , John P. Wikswo, Jr. ^*    and Franz Baudenbacher ^*  

^* Department of Biomedical Engineering; Department of Physics and Astronomy; Vanderbilt Institute for Integrative Biosystems Research and Education; and Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee

Correspondence: Address reprint requests to Franz J. Baudenbacher, Dept. of Biomedical Engineering and Physics, Vanderbilt University, 6301 Stevenson Center, Box 1807, Station B, Nashville, TN 37235. Tel.: 615-322-6361; Fax: 615-322-4977; E-mail: f.baudenbacher{at}vanderbilt.edu.

We magnetically imaged the magnetic action field and optically imaged the transmembrane potentials generated by planar wavefronts on the surface of the left ventricular wall of Langendorff-perfused isolated rabbit hearts. The magnetic action field images were used to produce a time series of two-dimensional action current maps. Overlaying epifluorescent images allowed us to identify a net current along the wavefront and perpendicular to gradients in the transmembrane potential. This is in contrast to a traditional uniform double-layer model where the net current flows along the gradient in the transmembrane potential. Our findings are supported by numerical simulations that treat cardiac tissue as a bidomain with unequal anisotropies in the intra- and extracellular spaces. Our measurements reveal the anisotropic bidomain nature of cardiac tissue during plane wave propagation. These bidomain effects play an important role in the generation of the whole-heart magnetocardiogram and cannot be ignored.

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