The Effect Of Non-fourier Heat Transfer On Temperature Field Of Atrial Fibrillation During Microwave Ablation

Atrial fibrillation（AF）is a common arrhythmia in a clinic,and its serious complications affect the health of patients.Catheter ablation has become the main method in the treatment of AF.Its principle is to cause irreversible necrosis of myocardial tissue through electromagnetic heat,thus blocking abnormal electrical signal conduction.The thickness of myocardial tissue in the ablation site is about 1.4-7.7 mm.If reaching the transmural ablation,the ablation depth of myocardial tissue should be accurately predicted.The microwave ablation can produce greater ablation depth in a short time,it is more suitable for the treatment of AF.However,due to the complexity of myocardial tissue,the characteristics of high energy and the short time of microwave heating,the microwave ablation process of AF no longer meets the Fourier heat transfer law.The finite velocity of heat transfer in myocardial tissue should be considered,so the Non-Fourier heat transfer law is introduced.Non-Fourier heat transfer considers that there is a phase delay between the propagation of heat flux vector and the formation of a temperature gradient,and that is relaxation time.But it is not enough to study the temperature field distribution using Non-Fourier heat transfer law in the numerical simulation of microwave ablation of AF at present.And there are few studies that quantify the influence of different factors（ablation time,ablation power,myocardial blood perfusion rate,myocardium-blood convection heat transfer coefficient）on ablation effect under Non-Fourier heat transfer law.In this study,the relaxation time of myocardial tissue was measured by experiment,and the Non-Fourier heat transfer effect of microwave ablation of AF was simulated by the finite element method.The influence of the Non-Fourier heat transfer effect on the temperature field distribution of myocardial tissue and the different factors of microwave ablation of AF were discussed.The specific research contents are as follows:1.The effect of Non-Fourier heat transfer on the temperature field of microwave ablation of AF.First,the relaxation time of myocardial tissue was measured.In this experiment,the heatwave propagation velocity in the isolated pig heart tissue was measured,and the relaxation time of the myocardial tissue was calculated and analyzed.Then,the classical one-dimensional Pennes Fourier heat transfer model（Pennes）,the Hyperbolic Non-Fourier heat transfer model（Hyperbolic）and dual-phase-lag Non-Fourier heat transfer model（DPL）were used to construct the idealized three-dimensional model of microwave ablation of AF.The highest temperature,ablation depth and ablation width under ablation time within 60 s,different ablation power（30W,40 W,50 W,60 W）,myocardial blood perfusion rate（609 ml/min/kg,840 ml/min/kg,1026 ml/min/kg,1719 ml/min/kg）and myocardium-blood convection heat transfer coefficient（0 W/m~2·K,529W/m~2·K,1024 W/m~2·K,1464 W/m~2·K）were obtained by means of coupling of electromagnetic field and temperature field.It analyzed that the influence of the Non-Fourier heat transfer（Hyperbolic model,DPL model）effect on the temperature field of microwave ablation of AF.2.The influence factors of microwave ablation of AF.The Taguchi experiment design and analysis of variance were used to get the ablation depth under different experimental groups.According to the results of main effect diagram and variance contribution rate,the effects of ablation time,ablation power,myocardial blood perfusion rate and myocardium-blood convective heat transfer coefficient on ablation depth were analyzed.The results were as follows:1.The relaxation time of pig heart tissue was measured in vitro,and the relaxation time was 5.36±0.35 s.The numerical simulation results showed that:（1）The highest temperature of myocardial tissue calculated by the Hyperbolic model and DPL model was different from that of the Pennes model within 40 s.When the ablation power was60 W and the ablation time was 5 s,the highest temperature of myocardium in Pennes model,Hyperbolic model and DPL model was 124.55℃,104.47℃and 101.67℃,respectively.（2）The ablation depth and the ablation width obtained by Non-Fourier heat transfer were smaller than those obtained by Fourier heat transfer.When the ablation power was 60 W and the ablation time was 5 s,the ablation depth and the ablation width under Non-Fourier heat transfer were the most different from Fourier heat transfer.At this time,the ablation depth of the Pennes model,Hyperbolic model and DPL model was 3.04 mm,2.1 mm and 2.01 mm,and the ablation width was 6.67mm,5.09 mm and 5 mm,respectively.The ablation depth and the ablation width of the Hyperbolic model and DPL model were less than 0.1 mm.2.The results of influence factor analysis showed that:the contribution rate of ablation time,ablation power,myocardial blood perfusion rate and myocardium-blood convection heat transfer coefficient was 70.83%,18.1%,6.25%,3.3%,respectively.There are two conclusions in this study:1.In the ablation time of 60 s,the lesion dimensions calculated by Non-Fourier heat transfer is always smaller than those calculated by Fourier heat transfer,and the difference is the largest when the ablation power is 60 W and the ablation time is 5 s.The ablation depth of the Hyperbolic model and DPL model is 0.94 mm and 1.03 mm smaller than that of the Pennes model.The Non-Fourier heat transfer should be used to predict the lesion dimensions of myocardial tissue.The Hyperbolic model and DPL model have the same temperature distribution,so the Hyperbolic model can be used to replace the more complex DPL model.2.The ablation time,ablation power had significant effects on ablation depth.In this study,the relaxation time of myocardial tissue was measured.And the influence of the Non-Fourier heat transfer law on the temperature field of microwave ablation of AF based on numerical simulation was analyzed.And the effects of different factors on microwave ablation were quantified.It provided a basic theoretical reference for clinical treatment.