Renal Artery Branch Denervation: Evaluation of Lesion Characteristics Using a Thermochromic Liquid Crystal Phantom Model

Comparison of ablation characteristics of three different radiofrequency applicators in renal sympathetic denervation

OBJECTIVE

Renal sympathetic denervation (RDN) is an alternative treatment for resistant hypertension (RH). This study aims to compare ablation effects using three radiofrequency applicators (i.e., balloon-based four electrodes, spiral and monopolar devices).

METHODS

An idealized three-dimensional model of the renal artery was established using COMSOL Multiphysics to mimic radiofrequency ablation (RFA). Radiofrequency (RF) energy was delivered to the tissue at the same simulation settings, i.e., 4, 6, and 8 W for 60 s, using the three abovementioned RF applicators. The temperature distribution in the tissue was calculated using the coupled electrical-thermal-fluid finite element method. Lesion borders were defined using 50 °C isotherms. The maximum lesion depth, width, area, and circumferential coverage rate were compared among the three applicators at a blood flow of 0.4 m/s. Monopolar RF ablations in a renal artery phantom model were performed to validate the reliability of the simulation method.

RESULTS

The balloon-based system yields greater lesion depths and widths compared with spiral and monopolar denervation under the same power. The range of maximum lesion depth is 1.58-3.11 mm for balloon-based RDN, 0.90-1.81 mm for spiral RDN and 1.12-2.38 mm for monopolar RDN, at a power of 4-8 W. The corresponding ranges of maximum lesion width are 2.22-5.73, 1.48-3.54, and 1.93-5.31 mm, respectively, and the circumferential coverage rates of the renal artery are 41.43%-91.99%, 31.71%-66.23%, and 9.55%-23.06%, respectively. The average velocity after balloon-based, spiral, and monopolar RDN increases by 3, 5, and 1 cm/s, respectively. The validation of the computer model offered prediction errors are <5% in terms of temperature at different locations (i.e., 2, 4, and 8 mm).

CONCLUSIONS

In terms of lesion size, balloon-based RDN appears to be the best option for the treatment of RH. However, the change in flow velocity in the arterial flow field suggests that its hemodynamic changes must be prioritized for investigating its safety. Although spiral catheter ablation yields the smallest lesion size and a significant change in flow velocity in the flow field, its coverage rate is larger than that of monopolar RDN; compared with balloon-based RDN, it did not obstruct most of the blood flow.

Flow Field Analysis in RF Ablation Based on PIV Experiment

Resistant hypertension (RH) is a major healthcare issue, causing cardiovascular and cerebrovascular diseases. In recent years, radiofrequency (RF) ablation to renal sympathetic denervation (RSD) is a new effective method for the treatment of RH. However, the effect of RSD on renal artery blood flow still need further research. In this study, Particle Image Velocimetry (PIV) experiment and RF ablation experiment were used to observe the blood flow states in three conditions: no ablation with flow, ablation with no flow, and ablation with flow. The results showed that when the blood flow was 1L/min in renal artery without ablation, it was uniform laminar flow. When the blood was static in renal artery with ablation, there was eddy around the ablation catheter. When the blood flow was 1L/min in renal artery with ablation, the eddy disappeared and the blood flow was uniform laminar flow. Therefore, when the renal artery blood flow is 1L/min, there will be no thrombus and hemolysis in the renal artery due to eddy current and large velocity gradient, which preliminarily verified the safety of the RSD. Keyword: Resistant hypertension; Radiofrequency ablation; Flow field; PIVClinical relevance-When the blood flow of renal artery is 1L/min, there will be no thrombus and hemolysis in renal artery due to eddy current and large velocity gradient during the operation of RF ablation to renal sympathetic denervation.