Extracellular measurement of anisotropic bidomain myocardial conductivities. I. Theoretical analysis.
The passive electrical properties of cardiac tissue, such as the intracellular and interstitial conductivities along the longitudinal and transverse axes, have not been often measured because intracellular electrodes are usually needed for these measurements. In this paper, we present a theoretical analysis of two myocardial models developed to estimate these properties by analyzing potentials recorded with a pair of extracellular electrodes while injecting alternating current between another pair of electrodes. First, the cardiac tissue is represented by a standard bidomain model which includes a membrane capacitance; second, this model is modified by adding an intracellular capacitance representing the intercalated disks. Numerical solutions are computed with a fast Fourier transform algorithm without constraining the anisotropy ratios of the interstitial and intracellular domains. We systematically investigate the effects of changes in the bidomain parameters on the voltage-to-current ratio curves. We also demonstrate how the bidomain parameters can be theoretically estimated by fitting, with a modified Shor's r algorithm, the simulated potentials along the longitudinal and transverse axes for different frequencies between 10 and 10,000 Hz. An important finding is that the interelectrode distance must be similar to the myocardial space constant so as to obtain frequency dependent measurements.
Le Guyader
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Institut de Génie Biomedical, Ecole Polytechnique de Montreal, Research Center of Hôpital du Sacré-Coeur de Montreal and Université de Montreal, Quebec, Canada.
Trelles
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Savard
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D000465:Algorithms; D016880:Anisotropy; D003198:Computer Simulation; D025802:Electric Capacitance; D004553:Electric Conductivity; D004558:Electric Stimulation; D005583:Fourier Analysis; D008564:Membrane Potentials / Q000502:physiology*; D008955:Models, Cardiovascular; D009206:Myocardium / Q000378:metabolism*