Individual custom-designed modelling for the finite element method to be used in the forward calculation of a body surface isopotential map.

Body surface potential maps differ considerably in their pattern even among normals, depending upon torso configuration. Thus individualized modelling of the heart-torso model is certainly desirable for a forward problem if it can be achieved without much effort. In this paper such a heart-torso model which is flexible enough to adapt to different body shapes with ease will be reported. As its basic structure, the innermost sphere represents the electromotive force of the heart, the outermost ellipsoid surface representing the torso surface and nine similar ellipsoid surfaces intervening between the two with step-wise increasing diameters were considered. We made 98 radiating penetration points for the innermost sphere as well as the 10 intervening ellipsoid surfaces. By making use of neighboring points of penetration as corners, the heart-torso model was divided into 4992 tetrahedral elements for a finite element method calculation. Once this basic structure was established, it was found to be very easy to be modified in a computer in order to make it fit to individual torso configurations quite faithfully by deforming the outermost ellipsoid. Individualized torso-heart models were built and their maps were simulated using data obtained from several healthy subjects. This paper discusses the results of two individuals, one muscular and the other slender, who exhibited considerably different body surface potential maps.