A 3-DIMENSIONAL FINITE-ELEMENT MODEL OF HUMAN TRANSTHORACIC DEFIBRILLATION - PADDLE PLACEMENT AND SIZE

A detailed 3-D finite element model of the conductive anatomy of the h uman thorax has been constructed to quantitatively assess the current density distribution produced in the heart and thorax during transthor acic defibrillation. The model is based on a series of cross-sectional CT scans and incorporates isotropic conductivities for eight tissues and an approximation of the anisotropic conductivity of skeletal muscl e, Current density distributions were determined and compared for four paddle pairs and two paddle sizes, Our results show that the myocardi al current density distributions resulting from a defibrillation shock were fairly uniform for the paddle pairs and sizes examined in this s tudy. Specific details of the spatial distribution of the current dens ity magnitudes in the heart were found to depend on paddle placement a nd size, When the minimum current necessary to defibrillate was delive red, the maximum myocardial current density produced with any of the p addle sizes and positions examined was less than four times the minimu m current density necessary to render a myocyte in a fibrillating hear t inexcitable, and less than 40% of the damage threshold, These result s suggest that common clinically used defibrillation paddle positions have a safety margin as large as 2.5 for current and similar to 6 for energy.