Evaluating the thermal performance of a balloon-based renal sympathetic denervation system with array electrodes: a finite element study.

Renal denervation transmits radiofrequency (RF) energy through an electrode to treat resistant hypertension (RH), applying ablation in the renal artery. Several experimental studies have shown that this treatment has been used effectively to treat RH. The aim of this paper is to investigate the effect of ablation parameters (i.e., electrode length, applied voltage, ablation time, and blood flow) on the temperature distribution using a balloon-based array electrodes system. A simplified three-dimensional model including four electrodes and a balloon was established. The balloon diameter was 3 mm and placed in a 5 mm diameter renal artery for forming intra-arterial occlusion. Four electrodes were mounted on the balloon and distributed in the same plane to mimic circumferential RF ablation. Computer simulations were conducted to investigate the thermal performances of the device by setting different electrode configurations, treatment protocols, and physiological factors. The thermal performances including the thermal distribution, maximum lesion depth, length, and area were analyzed. The lesion shape of the array RF electrodes was approximately a sphere with a 100% circumference coverage rate of the renal artery. The lesion depth and length increase with each factor except for blood velocity. Increasing the electrode length from 2 to 4 mm or 2 to 6 mm, the lesion depth increases by 1.15 mm and 0.54 mm at 60 s. The corresponding lesion length increases by 2.65 mm and 2.34 mm, respectively. The range of effective lesion depth is 1.90-4.90 mm, at a voltage of 15-30 V. But the peak temperature at the arterial outer wall exceeded 100 °C when the voltage is above 25 V. In tissue, the degree of thermal injury in the 2 mm area reached 100%, but in blood was not more than 5%. There was no significant difference at different flow conditions because the difference value in lesion depth was not exceeded 0.5 mm. The results showed that the balloon-based four electrodes system is expected to overcome the difficulty of incomplete ablation. In clinical application, 2 mm-electrode is recommended to avoid long wall damage as much as possible and control the voltage below 25 V. This treatment has little thermal injury on the blood, which means it may avoid coagulation formation. Moreover, the application of this device does not need to consider the difference in individual blood velocity.