Comprehensive Assessment of Human Accessory Renal Artery Periarterial Renal Sympathetic Nerve Distribution

Aspects of renal function and renal artery anatomy as indications for renal denervation

Renal denervation (RDN) is a minimally invasive, endovascular catheter-based procedure using radiofrequency, ultrasound, or alcohol-mediated ablation to treat resistant hypertension. As more attention is focused on the renal sympathetic nerve as a cause and treatment target of hypertension, understanding the anatomy of the renal artery may have important implications for determining endovascular treatment strategies as well as for future selection of devices and appropriate candidates for RDN treatment. However, the anatomical structure of the renal artery (RA) is complex, and standardized morphological evaluations of the RA structure are lacking. Computed tomography angiography or magnetic resonance angiography imaging is useful for assessing RA anatomy before conducting RDN. RA echocardiography is an established noninvasive screening method for significant stenosis. Major randomized controlled trials have limited enrollment to patients with preserved renal function, usually defined as an estimated glomerular filtration rate (eGFR) ≥ 45 mL/min/1.73 m2. Therefore, the level of renal function at which RDN is indicated has not yet been determined. This mini-review summarizes the characteristics of renal artery anatomy and renal function that constitute indications for renal denervation. (Role of Clinical Trials: K. Kario is an Executive Committee Principal Investigator for the Spyral OFF MED, the Spyral ON MED, the DUO and the REQUIRE; a Coordinating investigator for the TCD-16164 study; a Site Principal Investigator for the HTN-J, the Spyral OFF MED, the Spyral ON MED, the DUO, the REQUIRE and the TCD-16164 study). Evaluation of renal arteries for radiofrequency renal denervation. A Simultaneous quadrantal ablations at four sites in the main renal artery or the equivalent renal artery to the main renal artery. B If there is a renal artery branch with a diameter >3 mm in the middle of the main renal artery, this branch is the distal end of the main renal artery. In this case, four simultaneous and quadrantal ablations can be performed on the equivalent renal arteries. C Four simultaneous and quadrantal ablations can be performed in the branch renal artery. D Sonication should be spaced at least 5 mm (one transducer*) apart. Perform 2 to 3 mm proximal to the arterial bifurcation. Perform 2 to 3 mm distal to the abdominal aortic inlet.

The prevalence of accessory renal arteries in sudanese population in Khartoum State: a cross-sectional CT study from 2017 to 2020

BACKGROUND

Renal artery variations are clinically significant due to their implications for surgical procedures and renal function. However, data on these variations in Sudanese populations are limited. This study aimed to determine the prevalence and characteristics of renal artery variations in a Sudanese population.

METHODS

A cross-sectional retrospective study was conducted in Khartoum state from October 2017 to October 2020. A total of 400 Sudanese participants who underwent abdominal CT scans were included. Data on demographic characteristics, kidney measurements, and renal vasculature were collected and analyzed using descriptive statistics and inferential tests.

RESULTS

The mean age of participants was 46.7 ± 18 years, with a nearly equal gender distribution. Overall, renal artery variations were present in 11% of participants, with accessory renal arteries observed in 6% of the study population. Among those with accessory vessels, 50% were on the right side, 29.2% on the left, and 20.8% bilateral, distributed across hilar 29.2%, lower polar 29.2%, and upper polar 41.7% regions. No significant associations were found between accessory renal arteries and age or gender (p-value > 0.05). However, participants with accessory renal arteries exhibited significantly narrower width 5.0 ± 1.4 than those with no with accessory renal arteries 5.8 ± 1.1 (p-value 0.002) Early dividing renal arteries were found in 5% of participants, with nearly half being bilateral. No significant associations were found between the presence of early dividing renal arteries and demographic or renal measurements (p-value > 0.05).

CONCLUSION

This study provides valuable insights into the prevalence and characteristics of renal artery variations in a Sudanese population. The findings contribute to our understanding of renal anatomy in this demographic and can inform clinical practice and surgical planning, particularly in renal transplantation and other renal procedures.

Effect of Accessory Renal Arteries on Essential Hypertension and Related Mechanisms

BACKGROUND

This case-control study aimed to determine whether there were differences between patients with essential hypertension with accessory renal arteries (ARAs) and those without ARAs.

METHODS AND RESULTS

The enrolled patients with essential hypertension were divided into the ARA group (n=200) and control group without ARAs (n=238). After propensity matching, 394 patients (197 in each of the 2 groups), were included. The 24-hour BP (4.33/2.43 mm Hg) and daytime BP (4.48/2.61 mm Hg) of patients in the ARA group were significantly higher than those of the control group (P<0.05). The flow-mediated dilation was lower in the ARA group (5.98±2.70 versus 5.18±2.66; P<0.05). In correlation analysis, the horizontal plasma aldosterone concentration had the highest correlation with 24-hour, daytime, and nighttime systolic BP (r=0.263, 0.247, and 0.243, respectively; P<0.05) and diastolic BP (r=0.325, 0.298, and 0.317, respectively; P<0.05). As for multivariate regression analysis, plasma aldosterone concentration was a significant risk factor for elevated 24-hour, daytime, and nighttime systolic BP (β=0.249 [95% CI, 0.150-0.349], 0.228 [95% CI, 0.128-0.329], and 0.282 [95% CI, 0.187-0.377], respectively; P<0.05) and elevated diastolic BP (β=0.289 [95% CI, 0.192-0.385], 0.256 [95% CI, 0.158-0.353], and 0.335 [95% CI, 0.243-0.427], respectively; P<0.05). Direct renin concentration was also a risk factor for 24-hour and daytime BPs, whereas heart rate was a risk factor correlated with 24-hour, daytime, and nighttime diastolic BP (all P<0.05). For the mixed-effects model for repeated measures, the results were similar to results of the multivariate regression analysis (all P<0.05).

CONCLUSIONS

ARAs could contribute a higher BP of patients with essential hypertension and might promote the development of essential hypertension. The mechanism might be related to overactivation of the renin-angiotensin-aldosterone system and sympathetic nervous system.

Histological examination of renal nerve distribution, density, and function in humans

BACKGROUND

Renal denervation is optimised when guided by knowledge of nerve distribution.

AIMS

We aimed to assess sympathetic nerve distribution along the renal arteries, especially in post-bifurcation vessel segments.

METHODS

Renal arteries and surrounding tissue from 10 body donors were collected and examined histologically. Immunohistochemical staining was used to analyse nerve distribution and to identify afferent and efferent sympathetic nerves.

RESULTS

A total of 6,781 nerves surrounding 18 renal arteries were evaluated. The mean lumen-nerve distance of the left renal artery (2.32±1.95 mm) was slightly greater than the right (2.29±2.03 mm; p=0.161); this varied across the arteries' courses: 3.7±2.3 mm in proximal segments, 2.5±2.0 mm in middle segments, 1.9±1.6 mm in distal prebifurcation segments and 1.3±1.0 mm in post-bifurcation segments (p<0.001). The number of nerves per quadrant was highest in the proximal segments (13.7±18.6), followed by the middle (9.7±7.9), distal prebifurcation (8.0±7.6), and distal post-bifurcation (4.3±4.0) segments (p<0.001). Circumferentially, the number of nerves was highest in the superior (7.8±9.4) and the ventral (7.6±13.1) quadrants (p=0.638). The mean tyrosine hydroxylase (TH) to calcitonin gene-related peptide (CGRP) ratio increased from proximal (37.5±33.5) to distal (72.0±7.2 in the post-bifurcation segments; p<0.001). Thirty-eight neuroganglia were identified along 14 (78%) renal arteries.

CONCLUSIONS

Nerves converge to the renal arteries' lumen in the distal segments and along branches, resulting in the lowest number of nerves per quadrant and the shortest lumen-nerve distance in the distal post-bifurcation segments. Efferent nerves occur predominantly, and the ratio of efferent to afferent nerves continues to increase in the vessels' course.

Anatomic Variations of Renal Arteries as an Important Factor in the Effectiveness of Renal Denervation in Resistant Hypertension

Hypertension remains the leading cause of death worldwide. Despite advances in drug-based treatment, many patients do not achieve target blood pressure. In recent years, there has been an increased interest in invasive hypertension treatment methods. Long-term effects and factors affecting renal denervation effectiveness are still under investigation. Some investigators found that the renal arteries' morphology is crucial in renal denervation effectiveness. Accessory renal arteries occur in 20-30% of the population and even more frequently in patients with resistant hypertension. Diversity in renal vascularization and innervation may complicate the renal denervation procedure and increase the number of people who will not benefit from treatment. Based on previous studies, it has been shown that the presence of accessory renal arteries, and in particular, the lack of their complete denervation, reduces the procedure's effectiveness. The following review presents the anatomical assessment of the renal arteries, emphasizing the importance of imaging tests. Examples of imaging and denervation methods to optimize the procedure are presented. The development of new-generation catheters and the advancement in knowledge of renal arteries anatomy may improve the effectiveness of treatment and reduce the number of patients who do not respond to treatment.

Effect of Renal Denervation on the Plasma Adiponectin Concentration in Patients with Resistant Hypertension

(1) Introduction: Adiponectin is synthetized by white adipose tissue and has anti-diabetic, anti-atherosclerotic, anti-thrombotic, anti-inflammatory, and cardioprotective properties. In patients with arterial hypertension, plasma concentration of adiponectin is lower than in healthy subjects. Renal denervation, i.e., percutaneous ablation of fibers from the sympathetic nervous system located in the wall of the renal arteries by radio frequency waves, is a method of resistant arterial hypertension treatment. (2) The aim of this single center, interventional, clinical study was to assess the effect of renal denervation on the plasma adiponectin concentration in patients with resistant arterial hypertension. (3) Materials and methods: 28 patients (13 women, 15 men) aged 54.4 ± 9.2 years with resistant hypertension who underwent renal denervation using Simplicity catheters (Medtronic, Inc., Northridge, CA, USA) were enrolled in the study. Plasma adiponectin concentration was determined using the Human Adiponectin ELISA Kit (Otsuka Pharmaceutical Co, Tokyo, Japan) before the renal denervation and 6 and 12 months after this procedure. (4) Results: Blood pressure (BP) values before renal denervation and 6 and 12 months after this procedure were as follows: systolic BP 190.4 ± 24.5, 160.8 ± 14.5, 155.7 ± 17.9 mmHg (p < 0.001) and diastolic BP 111.7 ± 18.9, 88.9 ± 8.3, 91.2 + 10.2 mmHg (p < 0.001), respectively. Body mass index (BMI) before renal denervation, 6 and 12 months after this procedure were 31.5 ± 4.2, 30.5 ± 4.4, 30.2 ± 4.0 kg/m2, (p = 0.057), respectively. Plasma adiponectin concentration before the renal denervation and 6 and 12 months after this procedure were 4.79 (3.95; 9.49), 7.58 (5.04; 9.51), 6.62 (4.57; 11.65) [µg/mL] (p = 0.007), respectively. (5) Conclusions: Plasma adiponectin concentration increases significantly after successful renal denervation in patients with resistant hypertension. Higher plasma adiponectin concentration may participate—beyond blood pressure reduction—in the cardiovascular benefits related to successful renal denervation; however’ clinical consequences of these results need further investigations.

Translational value of preclinical models for renal denervation: a histological comparison of human versus porcine renal nerve anatomy

BACKGROUND

Preclinical models have provided key insights into the response of local tissues to radiofrequency (RF) renal denervation (RDN) that is unobtainable from human studies. However, the anatomic translatability of these models to the procedure in humans is incompletely understood.  Aims: We aimed to compare the renal arterial anatomy in normotensive pigs treated with RF-RDN to that of human cadavers to evaluate the suitability of normotensive pigs for determining the safety of RF-RDN.

METHODS

Histopathologic analyses were performed on RF-treated renal arteries in a porcine model and untreated control renal arteries. Similar analyses were performed on untreated renal arteries from human cadavers.  Results: In both human and porcine renal arteries, the median number of nerves was lower in the more distal sections (the numbers in the proximal, middle, distal, 1st bifurcation, and 2nd bifurcation sections were 65, 58, 47, 22.5, and 14.7 in humans, respectively, and 39, 26, 29, 16.5, and 9.3 in the porcine models, respectively). Renal nerves were common in the regions between arteries and adjacent veins, but only 3% and 13% of the renal nerves in humans and pigs, respectively, were located behind the renal vein. The semiquantitative score of RF-induced renal arterial nerve necrosis was significantly greater at 7 days than 28 days (0.98 vs 0.75; p=0.01), and injury to surrounding organs was rarely observed.

CONCLUSIONS

The distribution of nerve tissue and the relative distribution of extravascular anatomic structures along the renal artery was similar between humans and pigs, which validates the translational value of the normotensive porcine model for RDN.

Present Evidence of Determinants to Predict the Efficacy of Renal Denervation

Sympathetic overactivation is one of the main contributors to development and progress of hypertension. Renal denervation (RDN) has been evidenced by series of clinical trials for its efficacy and safety to treat overactivated sympathetic nervous system induced diseases. However, the results were inconsistent and not all patients benefited from RDN. Appropriate patient selection and intraoperative factors to improve the efficacy of RDN need to be solved urgently. Over the decade, research studies on the correlations between indicators and the antihypertensive effects have been conducted and made a fairly well progress. Herein, we comprehensively reviewed the research studies on how to make RDN more predictable or improve the efficacy of RDN and summarized these potential indicators or devices which might be applied in clinical settings.

Renal artery variations in patients with mild-to-moderate hypertension from the RADIANCE-HTN SOLO trial

PURPOSE

To assess the variability of renal artery (RA) anatomy and presence of RA-pathology in patients with mild-to-moderate hypertension enrolled in the RADIANCE-HTN SOLO trial.

BACKGROUND

RADIANCE-HTN SOLO was a multicenter, international, blinded, randomized, sham-controlled trial evaluating ultrasound-based endovascular renal denervation (RDN) in patients with mild-to-moderate hypertension while off antihypertensive medications.

METHODS

Eligible subjects had pre-randomization renal CT- or MR- angiography (CTA, MRA) to confirm anatomic suitability and to define RA ablation sites. All images were sent for independent review for evaluation of RA anatomy and other vascular pathology.

RESULTS

A total of 324 patients underwent RA imaging (282 CTA and 42 MRA). Of those, 178 had simple anatomy with a single left and single right RA with mean diameters of 5.4 ± 0.9 and 5.1 ± 0.8 mm and mean lengths of 40.0 ± 12.9 and 52.0 ± 13.1 mm, respectively. Twenty-seven patients (8.3%) had unilateral or bilateral dual RAs with mean diameters of 4.0 ± 0.9 mm on the left and 3.9 ± 0.9 mm on the right. Forty percent (129/324) of patients had at least 1 accessory RA, with mean accessory diameters of 2.4 ± 0.8 mm on the left and 2.3 ± 0.8 mm on the right. Twenty-eight patients (8.6%) had at least 1 short (<25 mm) main RA. Incidental findings included: 9 patients (2.8%) with atherosclerotic RA stenosis ≥30%, 9 patients (2.8%) with fibromuscular dysplasia of RA and 2 patients (0.6%) with kidney and adrenal gland tumors.

CONCLUSIONS

Pre-procedure CTA or MRA imaging is a valuable aid in assessing RA anatomy prior to RDN because of variable RA anatomy. CTA or MRA may detect RA lesions, and renal or adrenal tumors which may need additional workup prior to consideration of RDN.

CLINICAL TRIAL REGISTRATION

ClinicalTrials.gov NCT02649426.

Paradise™ Ultrasound Renal Denervation System for the treatment of hypertension

Catheter-based renal denervation is a novel treatment approach for patients with hypertension and initial unblinded trials have shown promising results. The Paradise™ Ultrasound Renal Denervation System (ReCor Medical, CA, USA) is an ultrasound-based catheter with a distal balloon that acts as a coolant to protect the renal arterial wall. This device received CE-mark in 2012. Randomized, sham-controlled trials and postmarket studies have shown promising efficacy and safety results. Currently, three additional ongoing randomized, sham-controlled trials are underway in the USA, Europe, Japan and Korea, and the results will be pivotal in device approval in some of these countries. These studies with larger numbers of patients and longer duration of follow-up are needed to further confirm the safety and efficacy of this device.