| Atrial fibrillation(AF)is one of cardiac arrhythmia disease,which is common and harmful.It can cause thromboembolism,leading to cerebral apoplexy or stroke.The mechanism of radiofrequency(RF)ablation is the thermal effect of myocardial tissue in an alternating electromagnetic field.It leads to the increase of temperature to 50 ?.And at this temperature tissue will lose biological activity.So that it will block the abnormal conduction paths of AF,and restore sinus rhythm.RF ablation of AF has the advantage of less trauma,quicker recovery,and high success rate with low recurrence.It can significantly improve life of patients and decrease the incidence of sudden death,heart failure and stroke.Currently,the application of the ablation technique in clinical practice has become a first-line treatment option for part of patients with AF adaptive symptoms.The major objective of the dissertation is to study the thermal damage process and the experimental study of the bipolar RF ablation for AF.It includes three parts,theoretical study,finite element simulation analysis and experimental study.Mainly research carried out is as following:Theoretical study.The heat transfer process and model of RF ablation were analyzed.At the same time,the biological heat transfer model was introduced in detail,including the famous Pennes model,Chen and Holmes model(CH model),and TCEBE model and so on.Then the finite element analysis models of the single electrode and bipolar RF ablation were introduced.They were the basis for the next step of the finite element simulation analysis.Finite element method analysis.In the dissertation,the model of the bipolar RF ablation of the electric heat coupling field was established.The finite element simulation experiments did based on the Pennes bio-heat equation.And ANSYS Workbench 14.5 was the tool.The temperature distributions of the region under different experimental conditions were obtained.According to the temperature distribution,we can easily get the highest temperature,and the area at the boundary of 50 ?.By setting different parameters of the treatment,the best treatment parameter was obtained.By changing the property parameters of atrial tissue,the area and the highest temperature of the lesion decreased with the increase of the thermal conductivity and specific heat.In the contrary,the area and the highest temperature of the lesion increased with the increase of electrical conductivity.The results and analysis of single ablation and multiple ablation shows that multiple ablation is more effective for the isolation of myocardial tissue.Experimental research included in vitro and in vivo experiments.In vitro experiments were employed to investigate the pathological transmural rate of the ablated tissue.The pathological transmural rate of the tissue was found to decrease gradually with the increase of the thickness of the tissue.With the increase of the output power,the rate of pathological transmural gradually increased.In vivo experiments were utilized to investigate the immediate electrical isolation and long-term electrical isolation.The electrical isolation of the tissue after ablation was found by electrophysiological mapping epicardia.It was found that for either immediate or long-term electrical isolation of ablation tissue,the success rate of the output power of 30 W was always higher than that of the output power of 25 W.It verified the effectiveness and safety of 30 W,the treatment parameters obtained by simulation.By studying the effect of ablation times on the transmural rate of the tissue,we found that the transmural rate of the tissue with three times ablations were much higher than those of single ablation.Not only in pathological transmural rate,but also the immediate electrical isolation and long-term electrical isolation rate.And it was consistent with the finite element method results. |
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