MAGNETICALLY INDUCED CURRENTS IN THE CANINE HEART - A FINITE-ELEMENT STUDY

A moderately detailed three-dimensional (3-D) finite element model of the conductive anatomy of a canine thorax was used to determine the fi elds and currents induced by a time-varying magnetic held that has bee n shown to cause irregular heart beats in canines. The 3-D finite elem ent model of the canine thorax was constructed from CT scans and inclu des seven isotropic tissue conductivities and the anisotropic conducti vity of skeletal muscle. We use this model to estimate the stimulation threshold associated with stimulation of the heart by the time-varyin g magnetic field of a figure-eight coil. Variants of the thoracic mode l were also constructed to examine the sensitivity of model results to variations in model size, shape, and conductive inhomogeneity and ani sotropy. Our results show that myocardial fields were only mildly sens itive to thoracic size. However, model shape and conductive inhomogene ity and anisotropy substantially influenced the magnitude and distribu tion of myocardial fields and currents. Our results suggest that an in duced peak field magnitude of approximate to 1 V/cm is required to sti mulate the heart with the magnetic excitation simulated in this study.