Finite Element Analysis of Radiofrequency Ablation Abirvab Deb- BME M.Eng ‘14 Brice Lekavich- BME M.Eng ‘14 Cristian Vilorio- BME M.Eng ‘14

Background Radiofrequency Ablation What is it? -Arrhythmias -Tumors -Varicose Veins "Radiofrequency Ablation (RFA)." Johns Hopkins Medicine. Johns Hopkins Medicine, n.d. Web. 21 Apr

FEA Motivation Lesion has to be deep enough into targeted tissue, yet limit the amount of irreversible damage occurring to normal cardiac tissue The ablated tissue area has to be large enough to compensate for the uncertainties in the electrical mapping that is used to localize the target tissue. RF energy is effective in ablating some arrhythmias. Multiple attempts often have to be made prior to successfully destroying the targeted tissue Lesions produced are not deep enough to eliminate the target electrical pathway Lesion depth is a problem in the left ventricle where the heart wall is thick

Objective One of the most important reasons to model heat transfer in living tissues is to allow for the prediction of the level and area of potential damage caused by temperature change. We therefore aim to develop a model that allows for determination of the transient temperature distribution in living tissue under biological conditions and use this distribution to evaluate the potential lesion depth due to radiofrequency ablation. "Control Volume of Tissue Element." Body (Human) Heat Transfer. THERMOPEDIA, 10 Feb Web. 20 Apr

FEA Methodology Preprocessing - Geometry generation - Material Properties - Initial Conditions - Boundary Conditions - Mesh Generation Solution - Duration of RF energy - Time Steps Postprocessing - Temperature Distribution - Lesion Dimensions - Convergence Test

Bioheat Transfer & Pennes’ Equation There are two main approaches to bioheat transfer models: 1.Continuum approach- thermal impact of all blood vessels is accounted for by perfusion through the effective conductivity of the tissue 2.Vascular approach- models the impact of each vessel individually, attempting to reproduce the real vascularity of the tissue. The most widely used continuum model is that given by Harry Pennes (1948). Since then, multiple variations have been developed to improve or account for different factors. Pennes’ Bioheat Equation:

Assumptions of Pennes’ Equation 1)Pre-arteriole/post-venule heat transfer between the tissue and blood is neglected. 2)Blood flow in small capillaries is assumed to be isotropic (ignores blood flow directionality). 3)Does not consider local vascular geometry (role of larger blood vessels near capillary beds is neglected). 4)Blood is assumed to reach arterioles supplying the capillary beds at the body core temperature (assumed instantaneous exchange of energy and equilibrium with local tissue temperature). Sakaguchi et al. In Vitro Engineering of Vascularized Tissue Surrogates. Scientific Reports 3: 1316, 1-7 (2013). Cardiac cells vascularization

Modifying Pennes Bioheat Equation

Governing Equations BCs Temperature: Heat Flux: Convection: Weak form:

Time Integration

ANSYS Simulation: Constants TissueDensity, ρ (kg/m 3 ) Specific Heat, c p (J/kg·˚C) Thermal Conductivity, k (W/m ·˚C) Heart Liver Kidney Pancreas Lung

ANSYS Simulation: Results Contours

ANSYS Simulation: Results Lesion size

Lesion Size after 60sec of Ablation ~3.5 mm wide ~2 mm deep Overall, higher temperature contours hit an equilibrium where heat in is balanced by heat out. Tissue still continues to heat up as expected at lower temperatures

Convergence Test

Lesion Size by Tissue Type