Introduction. Radiofrequency ablation is the primary interventional therapy for treating tachycardias. Three dimensional finite element modeling, in vivo and in vitro experiments were used to understand the physics of ablation and to identify important parameters that affect ablative lesion size, ablation efficiency and safety. The experimental results were also used to validate the model findings.; Methods. Simulations were performed in a three dimensional geometry to study the effect of ground electrode location and duration of energy delivery on ablative lesions. The three dimensional model included material non-linearities and used a convective boundary condition to simulate the cooling provided by the blood. In vivo ablation in six adult sheep hearts was also performed to validate the effects of ground electrode location on lesions that were predicted by the model. This model was used to study the effect of blood flow on lesion dimensions and ablation efficiency. A twenty-seven channel temperature measurement system was developed to obtain in vitro temperature maps of extracted bovine cardiac tissue during ablation and to validate the computer model.; Results. A ground electrode location that would maximize the lesion size with highest ablation efficiency was identified. The largest lesion with the highest ablation efficiency was obtained when the ground electrode was placed directly opposite the catheter tip electrode with the target tissue between the two electrodes as compared to any other position of the ground electrode. Computer simulations also demonstrated that the ground electrode location had more significant effect on constant power ablation than on temperature controlled ablation. The in vitro experimental temperature measurements and computer simulations demonstrated that an increase in fluid flow resulted in smaller lesions with lower ablation efficiency. The fluid flow resulted in an asymmetric temperature distribution in the tissue and the blood along the electrode axis. The finite element model reproduced the qualitative features of the experimental data. However, the quantitative agreement between the modeling and experimental results was moderate using uniform material properties. The approach described here is vital to the development of a quantitatively accurate ablation model that can be used to predict and interpret thermal activity in the cardiac tissue and the blood during ablation. (Abstract shortened by UMI.)
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