FINITE ELEMENT MODELING OF RADIO-FREQUENCY CARDIAC AND HEPATIC ABLATION by

Ablation is the destruction of cardiac tissue to cure rhythm disturbances and of liver tissue to cure cancer. This work presents methods, numerical results, experimental results, and applications of finite element (FE) analysis for the study of radiofrequency (RF) cardiac and hepatic ablation. I outline a process for FE modeling implementations of temperature-controlled and power-controlled RF ablation and investigate the effects of changes in myocardial properties to the numeric results. I performed the Cauchy Convergence test to determine the optimal number of elements for our system and observed that the changes in myocardial properties affect the results of the FE analyses of power-controlled RF ablation more than that of temperature-controlled RF ablation. In this work I present FE analyses of the following ablation catheter designs. (1) A catheter that includes one or more needle electrodes with a diameter of 0.5 to 1.0 mm and length of 2.0 to 10 mm. The needle electrodes are capable of creating large lesions for curing ventricular tachycardia. (2) Conventional straight tip electrode with added curvatures and a iv resistive coating at the electrode−catheter interface to minimize the edge effect. I utilize FE analysis to demonstrate that there are hot spots at the edges of the conventional metal electrode and the insulating catheter. (3) Cylindrical-shaped long electrode with recessed edges, and a resistive material coating. (4) A 3-segment multielectrode catheter (MEC) ablation system. The last two catheter designs have potentials to create long thin lesions for the cure of atrial fibrillation. In this work I introduce the bipolar phase-shifted technique for RF energy delivery of MEC ablation. I determined the optimal phase-shift (φ) between the two sinusoidal voltage sources of a simplified two-dimensional FE model. At the optimal φ, the difference between temperatures at electrode edges is minimized. I present a diagram for a simplified bipolar phaseshifted MEC ablation system. In Chapter VI, I applied the FE method to study the effect of ablation sites and treatment time on the dimensions of the necrotic lesion in both temperatureand power-controlled RF catheter ablation using the conventional electrode design. Finally, I expand the application of FE analysis to RF hepatic ablation to develop a better understanding of the heating characteristics of the hepatic ablation probe. Our numeric data reveal that the shapes of the lesions created by the four-tine RF probe were mushroom-like, and were limited by the blood vessels. The temperature distribution in the two-dimensional model was highly nonuniform due to the presence of the bifurcated blood vessel.