OPTIMIZATION OF CARDIAC DEFIBRILLATION BY 3-DIMENSIONAL FINITE-ELEMENT MODELING OF THE HUMAN THORAX

The goal of this study was to determine the optimal electrode placemen t and size to minimize myocardial damage during defibrillation while r endering refractory a critical mass of cardiac tissue of 100%. For thi s purpose, we developed a 3-D finite element model with 55 388 nodes, 50 913 hexahedral elements, and simulated 16 different organs and tiss ues, as well as the properties of the electrolyte. The model used a no nuniform mesh with an average spatial resolution of 0.8 cm in all thre e dimensions. To validate this model, we measured the voltage across 3 -cm(2) Ag-AgCl electrodes when currents of 5 mA at 50 kHz were injecte d into a human subject's thorax through the same electrodes. For the s ame electrode placements and sizes and the same injected current, the finite element analysis produced results in good agreement with the ex perimental data. For the optimization of defibrillation, we tested 12 different electrode placements and seven different electrode sizes. Th e finite element analyses showed that the anterior-posterior electrode placement and an electrode size of about 90 cm(2) offered the least c hance of potential myocardial damage and required a shock energy of le ss than 350 J for 5-ms defibrillation pulses to achieve 100% critical mass. For comparison, the average cross-sectional area of the heart is approximate to 48 cm(2), about half of the optimal area. A second bes t electrode placement was with the defibrillation electrodes on the mi daxillary lines under the armpits. Although this placement had higher chances of producing cardiac damage, it required less shock energy to achieve 100% critical mass.