Effect of applied energy in renal sympathetic denervation with magnetic resonance guided focused ultrasound in a porcine model

Abstract

BackgroundPast catheter-based and focused ultrasound renal denervation studies have indicated that procedure efficacy is related to the number of ablations performed or the amount of energy used for the ablation. This study extends those prior results and investigates energy level effects on the efficacy of MR guided focused ultrasound renal denervation performed in a porcine model.MethodsTwenty-four normotensive pigs underwent unilateral denervation at three intensity levels. The applied intensity level was retrospectively de-rated to account for variability in animal size. Efficacy was assessed through evaluating the norepinephrine present in the kidney medulla and through histological analysis. The treatment was performed under MRI guidance including pre- and post-procedure T1-weighted and quantitative T1 and T2 imaging. During treatment, the temperature in the near field of the ultrasound beam was monitored in real time with MR temperature imaging. Energy delivery in the regions surrounding the renal artery was independently confirmed through an invasive fiberoptic temperature probe placed in the right renal artery.ResultsAnimals that underwent denervation at a de-rated acoustic intensity of greater than 1.2 kW/cm2 had a significantly lower norepinephrine concentration in the kidney indicating successful denervation. Images obtained during the treatment indicated no tissue changes in the kidneys as a function of the procedure but there were significant T1 changes present in the right lumbar muscles, although only one animal had indication of muscle damage at the time of necropsy.ConclusionsWhile MR guided focused ultrasound renal denervation was found to be safe and effective in this normotensive animal model, the results indicated the need to incorporate patient-specific details in the treatment planning of MRgFUS renal denervation procedure.

Optimal Strategy for HIFU-Based Renal Sympathetic Denervation in Canines

“…Insufficiently focused ultrasound delivery can result in inadequate temperature elevation at the target region, which can lead to failure of complete sympathetic nerve disruption. Previous studies ( 18 , 21 , 22 ) highlighted the role of insufficient ablation on the variability of BP response observed following RDN. Furthermore, Sakura et al ( 23 ) reported sympathetic nerve regeneration at 180 days after the RDN procedure with radiofrequency energy, which may be partially explained by insufficient energy delivery.…”

Advances in Renal Denervation in the Treatment of Hypertension

“…Swine or canines were used, because their renal systems are similar to those of humans. Several experimental studies [60][61][62][63][64] have shown that extracorporeal focused ultrasound ablation of the renal artery and nerve is safe and effective.…”

High Intensity Focused Ultrasound: Terapi Non-Invasif Efektif untuk Hipertensi Resisten

“…Persarafan simpatik ginjal memainkan peranan penting dalam patofisiologi hipertensi. 16 Nervus renalis efferen berasal dari otak, melewati medulla spinalis, mencapai ginjal melalui ganglia simpatis, berjalan di tunika adventitia arteri renalis dan menginervasi segmen perifer korteks renalis, kemudian berakhir di arteriol glomerulus. 17 Aktivasi serabut saraf efferen ginjal menyebabkan retensi garam dan cairan dan aktivasi sistem renin-angiotensin-aldosteron, yang pada akhirnya meningkatkan tekanan darah.…”

“…Penelitian pada hewan coba pernah dilakukan pada anjing 11 dan babi. 8,10,16 Dari penelitian tersebut didapatkan penurunan tekanan darah yang signifikan, yakni 15,9 mmHg pada tekanan sistolik dan 13,6 mmHg pada tekanan diastolik. 11 Ditemukan pula penurunan kadar norepinepfrin 8 dan tidak ditemukan adanya kerusakan jaringan sekitar seperti kulit, hepar, lien, ginjal, ureter dan usus halus.…”