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This paper assesses the effectiveness of including variable thickness and fiber orientation characteristics of the skeletal muscle layer in calculations relating epicardial and torso potentials. A realistic model of a canine torso which includes extensive detail about skeletal muscle layer thickness and fiber orientation is compared with two other uniformly anisotropic models: one of constant thickness and the other of variable thickness. First, transfer coefficients are calculated from the model data. Then torso potentials for each model are calculated from the transfer coefficients and measured epicardial potentials. The comparison of calculated and observed torso potentials indicates that a simple model consisting of a uniformly anisotropic skeletal muscle layer of 1.0-1.5 cm constant thickness significantly improves the model. However, if photographic slices of the canine torso are used to introduce more detailed data about the variation in skeletal muscle thickness and fiber orientation into the model, the agreement and between calculated and measured torso potentials decreased, although a finite element mesh of over 5000 nodes was used to describe the skeletal muscle in the more detailed model. One source of error increase was considered to be due to numerical discretization and could be reduced with a much finer mesh or by utilizing higher order polynomials to represent the potential distribution within each finite element. However, the results presented in this paper show that high precision computation (64-bit word length) on the mainframe IBM 3081 with an attached FPS-164 gives a slow rate of improvement with reduced discretization intervals and that utilizing higher order polynomials within each finite element gives an even slower rate of improvement.(ABSTRACT TRUNCATED AT 250 WORDS)

This paper presents a method for electrocardiographic and other bioelectric calculations combining the Green's function boundary integral technique with the finite element method. Both the boundary integral method and the finite element method have been used extensively in electrocardiography for calculating epicardial and torso potentials. The boundary integral method is well suited for finding potentials in regions of isotropic conductivity and is computationally efficient, requiring unknown potentials to be calculated on the bounding surfaces only. It also compares favorably in accuracy with the finite element method in those regions. The finite element method is used in solving for potentials in regions of anisotropic conductivity since no simplifying assumptions or transformations of anisotropic regions into isotropic regions before solution are required. Combining the two methods, using the boundary integral method in isotropic regions and the finite element method is anisotropic regions, allows the advantages of both methods to be exploited.