Finite Element Method Simulation Study Of Lesion Size In Cardiac Catheter Radiofrequency Ablation For Atrial Fibrillation

Atrial Fibrillation (AF) is the most common cardiac arrhythmia and its prevalence in a statistical population increases with age. Its persistent significant symptoms are very dangerous to people health. Catheter radiofrequency ablation (RFA) is now widely applied in clinic as a therapy for AF. Electric current from RFA ablates small areas of abnormal tissue to cut the accessory pathway. The lesion size of RFA is the most important criteria to evaluate ablation result. Many studies have focused on finite element method (FEM) to calculate temperature distribution and determine lesion size during RF catheter surgery and it has great value in surgery plan and medical ablation instrument invention.In the dissertation, FEM study on lesion size is performed in cardiac RFA. and various influencing factors are evaluated, then heat transfer equations suitable for RFA procedure are investigated and hyperbolic heat equation is applied to the model for the first time, furthermore a novel method is proposed to create specified ablation model based on heart anatomy, finally the modeling method is validated with published platform experiment result. The research in the dissertation proposes a method to develop RFA simulation platform in clinic and provides a reference for further study.The main content of the dissertation is followings:AF disease is introduced including its cause, signs, symptoms and therapy guidelines, and then cardiac catheter RFA is presented such as physical mechanism, instruments and surgery procedure. At last, recent progress in related FEM research on lesion size estimation is reviewed systematically and hot research topics are discussed.A3D cylinder ablation model is created based on the research by the John G. Webster group in University of Wisconsin-Madison. Pennes heat transfer equation is adopted to perform FEM simulation and the lesion size determination criteria is studied. Furthermore, lesion size influencing factors are evaluated one by one, such as model radius, ablation duration, voltage, convective coefficients, electrode contact status and tissue physical properties, etc. Most of studies adopt Pennes heat equation which is derived from Fourier theory. Fourier theory is based on macroscopical phenomenon and it doesn’t consider heat wave propaganda speed, so it is not suitable for rapid heating procedure. In the dissertation, study is performed on the heat transfer equations suitable for RFA procedure and hyperbolic heat equation derived from Non-Fourier heat theory is applied and it takes the thermal wave behavior into account. In RFA model, FEM is adopted to study the model with corresponding Pennes heat equation and hyperbolic heat equation. Different convection coefficients and voltages are applied to simulate different conditions. The results show that the lesion size difference ratio can reach20%in some periods of ablation. The difference is significant and the methodological study shows that hyperbolic method is more suitable for RFA model.In order to simulate ablation for actual surgery procedure, a novel method is proposed to create specified ablation model suitable for heart anatomy. FEM analysis study is performed based on cardiac CT data. At first, one detailed cardiac ablation model is created with CT heart inner surface mesh, and various electrode contact status can be specified by user selection. Then COMSOL scripts were called by MATLAB to perform FEM analysis. The temperature profile and ablation lesion size are estimated after simulation. It shows that ablation results vary obviously with electrode insertion angles and penetration depths. Besides, the lesion region shape is not isotropy due to complex and atactic heart chamber anatomy. The method lays the foundation of the RFA simulation platform in clinic.Finally, a comparison is carried out between the model in the dissertation with the published platform experiment result by Sytske Foppen in Eindhoven University of Technology,2009. It shows that simulation result is consistent with that of the experiment. It validates the modelling method and indicates that the specified model based on heart anatomy will make results more precise.