Effect of paddle placement and size on defibrillation current distribution: a three-dimensional finite element model

A realistic three-dimensional finite-element model (FEM) of the conductive anatomy of a canine thorax was constructed for use in the study of transthoracic electrical defibrillation. The model was constructed from a series of 21 cross-sectional computed tomography (CT) scans of a 14.5 kg beagle, each separated by 0.82 cm. The electrical conductive properties of eight distinct tissues were incorporated, including the anisotropic properties of skeletal muscle. Current density distributions were obtained for six paddle pairings and two paddle sizes. A quantitative basis for comparing the resulting distributions was formulated. The results suggest that placing one or both of the paddles near the heart delivers a higher fraction of current to the heart. However, such placements also produce a less uniform myocardial current density distribution and thus have a higher potential for causing damage. Some paddle positions produced myocardial current densities close to the threshold for damage in successful defibrillations. The results indicate that 12 cm paddles may offer modest advantages over 8 cm paddles in clinical defibrillation.