Acute changes in morphology and renal vascular relaxation function after renal denervation using temperature-controlled radiofrequency catheter

Investigations of Laser-Assisted Renal Denervation for Treatment of Resistant Hypertension

BACKGROUND AND OBJECTIVES

Renal denervation (RDN) is an emerging surgical treatment for resistant hypertension. However, the current RDN using radiofrequency can cause undesirable thermal damage to the medial and luminal layers due to direct contact between the arterial lumen and energy source. The aim of this study is to evaluate the feasibility of the new laser-assisted RDN by exploring the potential treatment conditions.

METHODS

For ex vivo testing, six different treatment conditions (10 and 20 W applied for delivery of 300, 450, and 600 J) were tested on the porcine liver and renal artery (RA) by using a continuous wave 1064 nm laser wavelength. The ablated area in the liver tissue was measured to estimate the extent of the coagulated area. Histological evaluation was performed on the treated RA tissues to confirm the extent of thermal nerve damage.

RESULTS

The ablated depth, length, and area in the liver tissue increased with laser power and total energy. According to the histological results, 20 W groups yielded more significant damage to the RA nerves than 10 W groups at the total energy of 300 J (0.0 ± 0.0 mm for 10 W vs. 2.9 ± 1.0 mm for 20 W), 450 J (1.9 ± 0.6 mm for 10 W vs. 6.8 ± 1.5 mm for 20 W), and 600 J (2.9 ± 0.4 mm for 10 W vs. 7.3 ± 0.8 mm for 20 W). The treated RA exhibited insignificant medial injury in depth (medial thinning ≤ 25%), and no difference in the medial thinning was found among the six groups (p = 0.4).

CONCLUSION

The current study demonstrated that the 1064 nm laser at 20 W with delivery of 450 J could effectively damage the RA nerves with no or minimal injury to the surrounding tissue. The proposed laser-assisted RDN may enhance physiological effects with insignificant complications in in vivo situations. Further in vivo studies will be conducted to validate the current findings by evaluating the extent of blood pressure reduction and norepinephrine changes after the laser-assisted RDN on a large animal model.

Laser renal denervation: A comprehensive evaluation of microstructural renal artery lesions

Renal artery denervation (RDN) has been proposed for resistant arterial hypertension. Beyond conventional radiofrequency (RF) ablation, there are emerging RDN technologies, including laser catheter ablation. We aimed at evaluamting the local effects of laser ablation on the renal artery and perivascular nerve injury in comparison with radiofrequency ablation. Thirteen pigs (mean weight 36.7 ± 4.7 kg, age 3 months) were divided into three groups: (1) laser ablation in normotensive pigs (LA; n = 3), (2) bipolar RF ablation in normotensive pigs (RF; n = 7), and (3) a sham group (SHAM; n = 3). Transcatheter laser and RF ablations were performed under general anesthesia. After euthanasia, pathology and immunohistochemical studies were performed. Artery wall and perivascular nerve lesions were found in the LA and RF groups. A lower rate of intimal microdissections was evaluated after laser ablation when compared with RF ablation (0 vs. 1.5 [1;2.75] per artery; p < .05). There was a numerical prevalence of nerves with tyrosine hydroxylase expression loss after laser RDN when compared with RF ablation (16.7 [4; 18] vs. 9.1 [0;18] per specimen). Laser ablation is noninferior to RF ablation regarding perivascular nerve injury and is associated with less intimal layer damage.

Extended Renal Artery Denervation Is Associated with Artery Wall Lesions and Acute Systemic and Pulmonary Hemodynamic Changes: A Sham-Controlled Experimental Study

Objectives

We sought to assess acute changes in systemic and pulmonary hemodynamics and microscopic artery lesions following extended renal artery denervation (RDN).

Background

RDN has been proposed to reduce sympathetic nervous system hyperactivation. Although the effects of RDN on systemic circulation and overall sympathetic activity have been studied, data on the impact of RDN on pulmonary hemodynamics is lacking.

Methods

The study comprised 13 normotensive Landrace pigs. After randomization, 7 animals were allocated to the group of bilateral RDN and 6 animals to the group of a sham procedure (SHAM). Hemodynamic measures, cannulation, and balloon-based occlusion of the renal arteries were performed in both groups. In the RDN group, radiofrequency ablation was performed in all available arteries and their segments. An autopsy study of the renal arteries was carried out in both groups.

Results

The analysis was performed on 12 pigs (6 in either group) since pulmonary thromboembolism occurred in one case. A statistically significant drop in the mean diastolic pulmonary artery pressure (PAP) was detected in the RDN group when compared with the SHAM group (change by 13.0 ± 4.4 and 10.0 ± 3.0 mmHg, correspondingly; P = 0.04). In 5 out of 6 pigs in the RDN group, a significant decrease in systemic systolic blood pressure was found, when compared with baseline (98.8 ± 17.8 vs. 90.2 ± 12.6 mmHg, P = 0.04), and a lower mean pulmonary vascular resistance (PVR) (291.0 ± 77.4 vs. 228.5 ± 63.8 dyn∗sec∗cm⁻⁵, P = 0.03) after ablation was found. Artery dissections were found in both groups, with prevalence in animals after RDN.

Conclusions

Extensive RDN leads to a rapid and significant decrease in PAP. In the majority of cases, RDN is associated with an acute lowering of systolic blood pressure and PVR. Extended RDN is associated with artery wall lesions and thrombus formation underdiagnosed by angiography.

Aggravated endothelial endocrine dysfunction and intimal thickening of renal artery in high-fat diet-induced obese pigs following renal denervation

Background

Renal denervation (RDN) targeting the sympathetic nerves in the renal arterial adventitia as a treatment of resistant hypertension can cause endothelial injury and vascular wall injury. This study aims to evaluate the risk of atherosclerosis induced by RDN in renal arteries.

Methods

A total of 15 minipigs were randomly assigned to 3 groups: (1) control group, (2) sham group, and (3) RDN group (n = 5 per group). All pigs were fed a high-fat diet (HFD) for 6 months after appropriate treatment. The degree of intimal thickening of renal artery and the conversion of endothelin 1 (ET-1) receptors were evaluated by histological staining. Western blot was used to assess the expression of nitric oxide (NO) synthesis signaling pathway, ET-1 and its receptors, NADPH oxidase 2 (NOX2) and 4-hydroxynonenal (4-HNE) proteins, and the activation of NF-kappa B (NF-κB).

Results

The histological staining results suggested that compared to the sham treatment, RDN led to significant intimal thickening and significantly promoted the production of endothelin B receptor (ET_BR) in vascular smooth muscle cells (VSMCs). Western blotting analysis indicated that RDN significantly suppressed the expression of AMPK/Akt/eNOS signaling pathway proteins, and decreased the production of NO, and increased the expression of endothelin system proteins including endothelin-1 (ET-1), endothelin converting enzyme 1 (ECE1), endothelin A receptor (ET_AR) and ET_BR; and upregulated the expression of NOX2 and 4-HNE proteins and enhanced the activation of NF-kappa B (NF-κB) when compared with the sham treatment (all p < 0.05). There were no significant differences between the control and sham groups (all p > 0.05).

Conclusions

RDN aggravated endothelial endocrine dysfunction and intimal thickening, and increased the risk of atherosclerosis in renal arteries of HFD-fed pigs.