Paddle position and size effects in human transthoracic defibrillation- a three-dimensional finite element model

A realistic three-dimensional (3D) finite element model (FEM) of the conductive anatomy of a human thorax has been constructed to quantitatively assess the current density distribution produced in the heart and thorax during transthoracic defibrillation. The model is based on a series of cross-sectional CT scans and incorporates isotropic conductivities for 8 tissues and an approximation of the anisotropic conductivity of skeletal muscle. Current density distributions were determined for 4 paddle pairings and 2 paddle sizes. Our results show fairly uniform myocardial current density distributions for all paddle pairs and sizes examined. Maximum current density values < 4 times the minimum current density (Jlh) necessary to inactivate a myocyte suggest that common clinically used defibrillation paddle positions have a safety factor of at least 2.5.