Radiofrequency Ablation Power Supply Design Incorporating Multi-frequency Impedance Measurement

Radiofrequency ablation is the main method for the treatment of arrhythmia,atrial fibrillation and ventricular tachycardia.During radiofrequency ablation,the power of radiofrequency ablation power,ablation duration,myocardial tissue temperature,myocardial tissue impedance and other factors will affect the effect of radiofrequency ablation.With the wide application of radiofrequency ablation technology in clinical practice,the influence of changes in cardiac tissue impedance on radiofrequency ablation has become a hot topic in the field of radiofrequency ablation.In order to analyze the influence of myocardial tissue impedance,a multi-physical finite element model of temperature,solid mechanics and electric field was constructed by COMSOL Multiphysics,and a radiofrequency ablation power source with impedance measurement function was designed.The main contents are as follows:Firstly,combined with the AC electric field equation,heat transfer equation,solid mechanics equation and thermal damage evaluation equation during radiofrequency ablation,a multi-physical field coupled constant power radiofrequency ablation model of myocardial tissue was established.Based on the calculation results of the simulation model,it can be seen that with the increase of radiofrequency ablation power,the myocardial tissue temperature will gradually increase,the thermal damage area will gradually become larger,and the effect of myocardial tissue impedance reduction is more obvious.In addition,in the practical application of radiofrequency ablation,due to the different posture of different patients,the thickness of the fat in the myocardium will also be different,resulting in the different baseline impedance of the myocardium in different patients.Therefore,the influence of different baseline impedance on ablation damage was also analyzed in the finite element simulation.It can be seen that the larger the baseline impedance is,the larger the ablation damage volume and depth will be.The impedance spectrum information of myocardial tissue during radiofrequency ablation was measured under small voltage excitation signals of different frequencies.It can be seen that the decrease effect of myocardial tissue impedance is most obvious in the range of 1k Hz-500 k Hz.Secondly,in order to verify the finite element simulation model,a design scheme of RF ablation power supply was proposed and verified by Multisim circuit simulation software.Firstly,a low-voltage AC signal with a frequency of 500 k Hz and a amplitude of 0.6V is generated by direct digital frequency synthesis technology(DDS).Then,a two-stage voltage amplifier circuit is built through AD844 and PA84 operational amplifiers to amplify the output signal of DDS,and a high-voltage AC signal with a amplitude of about 30 V is obtained.Class A and B power amplifier circuit is used to amplify the current of the preceding circuit.Then,the real-time power of the RF ablation power is collected,and the PID control algorithm is used to keep the power constant.In addition,a low-voltage multi-frequency square wave impedance measurement signal and high-voltage ablation signal are designed to be superimposed together.In the process of radiofrequency ablation,the response signals at both ends of the myocardial tissue are collected.After the band-stop filter is processed,the changes of myocardial tissue impedance at different frequencies can be obtained by Fourier transform.Finally,a hardware platform for radio-frequency ablation power supply with impedance measurement function was built to evaluate the output signals of the hardware,and a constant-power power platform was built using the single-chip microcomputer STM32.After adjustment by PID controller,the final output power reached a stable state.In addition,radiofrequency ablation of myocardial tissue was conducted with this hardware device.After a period of time,obvious damage could be formed in myocardial tissue.Changes in myocardial impedance and impedance spectrum information were collected during the experiment.The results show that this power source can be used in the field of radiofrequency ablation of myocardial tissue and can collect the impedance information of myocardial tissue during radiofrequency ablation.