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 fields and currents induced by a time-varying magnetic field that has been shown to cause irregular heart beats in canines. The 3-D finite element model of the canine thorax was constructed from CT scans and includes seven isotropic tissue conductivities and the anisotropic conductivity of skeletal muscle. The authors use this model to estimate the stimulation threshold associated with stimulation of the heart by the time-varying magnetic field of a figure-eight coil. Variants of the thoracic model were also constructed to examine the sensitivity of model results to variations in model size, shape, and conductive inhomogeneity and anisotropy. The authors´ results show that myocardial fields were only mildly sensitive to thoracic size. However, model shape and conductive inhomogeneity and anisotropy substantially influenced the magnitude and distribution of myocardial fields and currents. The authors´ results suggest that an induced peak field magnitude of ≈1 V/cm is required to stimulate the heart with the magnetic excitation simulated in this study.