Effect Of Array Radiofrequency Ablation Electrodes On Renal Artery

Resistant Hypertension(RH)is a major global healthcare issue,causing cardiovascular and cerebrovascular diseases.Renal sympathetic denervation(RSD)is a new and effective method for the treatment of RH.This procedure transmits radiofrequency energy(RF)through electrodes to treat RH,applying ablation in the blood vessels.Studies have shown that the renal sympathetic nerves are damaged at therapeutic temperature(45?).Because the traditional treatment method only contains a single electrode.Unipolar therapy requires several rotations in the renal artery for single-point ablation,making a 360° complete ablation effect difficult.A balloon-based RSD device with an array of RF electrodes is proposed,and its effectiveness and safety thermally analyzed.The effects of this method on renal artery are analyzed through cell temperature sensitivity experiments and numerical simulation studies.The simulation results were validated through ex-vivo experiments using a unipolar RF electrode.The main research contents are as follows:(1)Cell experiment.First,we carried out the primary and passage culture for rat vascular endothelial cells.Then,these cells were identified by immunohistochemically identification.Next,the heat treatment model of rat vascular endothelial cells was constructed,and its proliferation activity at different temperatures(37-54?)and times(0h,24 h,48h)was detected by CCK8 reagent.Finally,the morphological changes of the cells were observed by HE staining.We preliminarily determined the temperature threshold for vascular endothelial cells to avoid the thermal damage.(2)Establishment of geometric models.The model was improved by adding balloon,catheter and guidewire.In addition,the array RF electrodes were constructed on the balloon(four circular electrode arrays were arranged in the same plane,the diameter of the electrode and balloon was 1 mm,2.25 mm or 3.0 mm,respectively).Based on the anatomical characteristics of renal artery,an ideal three-dimensional geometric model of renal artery was constructed(the arterial entrance diameter is 5mm,the diameter of bifurcation is 3.5mm,and the bifurcation angle is 50?).(3)Numerical simulation.The finite element analysis was carried out with Comsol Multiphysics software.The temperature distribution were obtained by coupling the electromagnetic field,temperature field and flow field.The maximum temperature position,depth and ablation area were calculated at different RF voltage(20V,25 V,28V,30V),blood velocity(0.4m/s,0.5m/s,0.8m/s)and balloon diameter(2.25 mm,3.0mm).(4)ex-vivo experiment.An open-loop blood circulation platform was built to perform unipolar RFA on the renal artery.The power was changed from 8W to 12 W,the time was 120 s,and the blood velocity was 2.56-5.12L/min.We observed the temperature changes in tissue and blood.The accuracy of the simulation was verified by ex-vivo experiments.Cell experiment results showed that: 1.Compared with the control group,the proliferation of endothelial cells was inhibited after heat treatment at 48? and 54? for 24 and 48 hours.The cell viability was 91.1±1.05% at 48? and 39.8%±1.43% at54? for 24 hours,83.9%±2.68% at 48? and 19.0%±2.68% at 54? for 48 hours respectively.The cell proliferation was significantly inhibited at 54?.2.When 37?<T< 48?,small part of the cells retracted slightly,and no cell shed.When 48?<T<50?,a large number of cells retracted circularly,and no cell exfoliation occurred.However,the temperature at 50-54?,there also are cell-shed occurs.3.To ensure the endothelial cells are not damaged,we determinate 48? as the safe threshold temperature.The numerical results showed that: 1.The array electrodes device can achieve 360°ablation effect.Whereas the effective ablation angle is only 68° for unipolar ablation.The proposed device overcomes the limitation of incomplete ablation for unipolar device.2.The temperature of the surrounding tissues is approximately 49?-63?,and the maximum ablation depth is about 5.0 mm away from the arterial inner wall.Balloon-based RSD devices can effectively ablate the peripheral renal sympathetic nerves.3.The maximum temperature of the central blood is approximately 41.9?.The ex-vivo experiments results showed that the temperature rise at different points,different power and different time are highly consistent with the simulation under the same conditions.The maximum error between the simulation and the ex-vivo experiment was less than 20%.The safe threshold temperature for vascular intima were given by cell experiments.The effects of different parameters on the temperature field of renal artery was analyzed through simulations.The feasibility and effectiveness of RSD with array RF electrodes was verified by simulation,which provided basic theoretical reference for clinical treatment.