EFFECTS OF PADDLE PLACEMENT AND SIZE ON DEFIBRILLATION CURRENT DISTRIBUTION - A 3-DIMENSIONAL FINITE-ELEMENT MODEL

A realistic three-dimensional finite element model of the conductive a natomy of a canine thorax was constructed for use in the study of tran sthoracic electrical defibrillation. The model was constructed from a series of 21 cross-sectional CT scans of a 14.5 kg beagle, each separa ted by 0.82 cm. The electrical conductive properties of 8 distinct tis sues were incorporated, including the anisotropic properties of skelet al muscle. Current density distributions were obtained for six paddle pairings and two paddle sizes. A quantitative basis for comparing the resulting distributions was formulated. Our results suggest that placi ng one or both of the paddles near the heart delivers a higher fractio n of current to the heart. However, such paddle placements also produc e a less uniform myocardial current density distribution and thus have a higher potential for causing damage. We found that some paddle posi tions can produce myocardial current densities close to the threshold for damage in successful defibrillations. Results obtained for 8 and 1 2 cm paddles indicate that 12 cm paddles may offer modest advantages o ver 8 cm paddles in clinical defibrillation. Comparison of our results to available in vivo experimental data confirm the validity of the fi nite element method for examining continuum field variables pertinent to electrical defibrillation.