Anatomical and procedural determinants of catheter-based renal denervation

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.

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.

Correlation between Renal Artery Anatomy and Hypertension: A Retrospective Analysis of 3000 Patients

Objective

To assess the correlation between renal artery anatomy and blood pressure in Undiagnosed Hypertension and Diagnosed Hypertension.

Methods

The renal artery CT scanning imaging data and laboratory data of 3000 inpatients and outpatients were collected retrospectively in 4 centers of China. Morphometric parameters were assessed using the quantitative vascular analysis (unit: mM).

Results

687 cases (23.2%) had accessory renal arteries unilaterally, and 216 cases (7.3%) had bilateral accessory renal arteries, including left kidney 825 (27.9%) and right kidney 798 (27.0%). The presence of accessory renal arteries and renal artery branches was higher in the diagnosed hypertension group as compared with the undiagnosed hypertension group (MARB, pp < 0.001; ARA, p < 0.001; others, p < 0.001). Consequently, multivariate regression analysis showed that age (OR = 2.519 (95% CI: 0.990–6.411, p < 0.001)), dyslipidemia (OR = 1.187 (95% CI: 0.960–1.454, p = 0.007)), renal hilum Outside the main renal artery branch (MRAB) (OR = 2.069 (95% CI: 1.614–2.524, p = 0.002)), and accessory renal artery (ARA) (OR = 2.071 (95% CI: 1.614–2.634, p = 0.001)) were risk factors of hypertension. In addition, higher renin activity was associated with ARA patients (2.19 ± 2.91 vs. 1.75 ± 2.85, p < 0.001).

Conclusions

When comparing renal arteries side by side, the anatomical length of the renal arteries is significantly different. In addition, the prevalence of accessory renal arteries and renal artery branches is higher in the hypertension group. The auxiliary renal artery and the main renal artery branch outside the renal portal are independent factors of hypertension. Renal sympathetic nerve activity is affected by renin activity and is related to the accessory renal artery.

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.

Common trunk of the right accessory renal artery and right inferior phrenic artery originating from the thoracic artery: An unreported variation

Accessory renal arteries (ARAs) are common and usually originate from the abdominal aorta and the renal artery. Inferior phrenic arteries (IPAs) can also arise from the abdominal aorta or its branches. In this paper, we present the first case of a common trunk of the right ARA and right IPA arising from the thoracic artery at the level of T10, which was discovered by multidetector-row computed tomography in pretherapeutic evaluation and clearly confirmed by selective angiography. It is important to recognize this anatomical variation when performing cardiovascular and interventional radiological procedures.

Quantitative analysis of renal arterial variations affecting the eligibility of catheter-based renal denervation using multi-detector computed tomography angiography

Catheter-based renal denervation (RDN) was introduced to treat resistant hypertension. However, the reduction in blood pressure after the RDN was modest. Catheter-based RDN was performed only at main renal arteries, except for accessory and branch arteries due to the diameter being too small for the catheter to approach. Here, we retrospectively analyzed the anatomy of diverse renal arteries via 64-channel multi-detector computed tomography angiograms of 314 consecutive donors who underwent living donor nephrectomy from January 2012 to July 2017. Occurrence rates of one or more accessory renal arteries in donors were 25.3% and 19.4% on the left and right sides, respectively. Early branching rates before 25 mm from the aorta to the right and left renal arteries were 13.7% and 10.5%, respectively. Overall, 63.1% and 78.3% of donors had no accessory artery bilaterally and no branched renal artery, respectively. As a result, 47.1% had only main renal arteries without an accessory artery and early-branching artery. Approximately half of the donors had multiple small renal arteries bilaterally, for which catheter-based denervation may not be suitable. Thus, preoperative computed tomography angiography requires careful attention to patient selection, and there is a need for improved methods for denervation at various renal arteries.

A Three-Arm Randomized Trial of Different Renal Denervation Devices and Techniques in Patients With Resistant Hypertension (RADIOSOUND-HTN)

BACKGROUND

Both radiofrequency and ultrasound endovascular renal sympathetic denervation (RDN) have proven clinical efficacy for the treatment of hypertension. We performed a head-to-head comparison of these technologies.

METHODS

Patients with resistant hypertension were randomly assigned in a 1:1:1 manner to receive either treatment with (1) radiofrequency RDN of the main renal arteries; (2) radiofrequency RDN of the main renal arteries, side branches, and accessories; or (3) an endovascular ultrasound-based RDN of the main renal artery. The primary end point was change in systolic daytime ambulatory blood pressure at 3 months.

RESULTS

Between June 2015 and June 2018, 120 patients were enrolled (mean age, 64±9 years±SD; mean daytime blood pressure, 153/86±12/13 mm Hg). Of these, 39 were randomly assigned to radiofrequency main renal artery ablation, 39 to combined radiofrequency ablation of the main artery and branches, and 42 to ultrasound-based treatment. Baseline daytime blood pressure, clinical characteristics, and treatment were well balanced between the groups. At 3 months, systolic daytime ambulatory blood pressure decreased by 9.5±12.3 mm Hg ( P<0.001) in the whole cohort. Although blood pressure was significantly more reduced in the ultrasound ablation group than in the radiofrequency ablation group of the main renal artery (-13.2±13.7 versus -6.5±10.3 mm Hg; mean difference, -6.7 mm Hg; global P=0.038 by ANOVA, adjusted P=0.043), no significant difference was found between the radiofrequency ablation groups (-8.3±11.7 mm Hg for additional side branch ablation; mean difference, -1.8 mm Hg; adjusted P>0.99). Similarly, the blood pressure reduction was not found to be significantly different between the ultrasound and the side branch ablation groups. Frequencies of blood pressure response ≥5 mm Hg were not significantly different (global P=0.77).

CONCLUSIONS

In patients with resistant hypertension, endovascular ultrasound-based RDN was found to be superior to radiofrequency ablation of the main renal arteries only, whereas a combined approach of radiofrequency ablation of the main arteries, accessories, and side branches was not.

CLINICAL TRIAL REGISTRATION

URL: https://www.clinicaltrials.gov . Unique identifier: NCT02920034.

Renal artery anatomy assessed by quantitative analysis of selective renal angiography in 1,000 patients with hypertension

AIMS

With increasing attention to renovascular causes and targets for hypertension there arises a critical need for more detailed knowledge of renal arterial anatomy. However, a standardised nomenclature is lacking. The present study sought to develop a standardised nomenclature for renal anatomy considering the complexity and variation of the renal arterial tree and to assess the applicability of the nomenclature.

METHODS AND RESULTS

One thousand hypertensive patients underwent invasive selective renal artery angiography in nine centres. Further, renovasography was performed in 249 healthy swine as a surrogate for normotensive anatomy. Anatomical parameters were assessed by quantitative vascular analysis. Patients' mean blood pressure was 168/90±26/17 mmHg. The right main renal artery was longer than the left (41±15 mm vs. 35±13 mm, p<0.001), but the left had a greater diameter (5.4±1.2 vs. 5.2±1.2 mm, p<0.001). Accessory renal arteries and renal artery disease were documented in 22% and 9% of the patients, respectively. Other than exhibiting a longer left main renal artery in uncontrolled hypertensives (+2.7 mm, p=0.034) there was no anatomical difference between patients with controlled and uncontrolled hypertension. Main renal artery mean diameter was smaller in patients with impaired kidney function (GFR <90 ml/min, left -0.5 mm, right -0.4 mm, both p<0.001).

CONCLUSIONS

Renal arterial anatomy differs between sides but shows no difference between patients with and without blood pressure control. Impaired GFR was associated with small main renal artery diameter.

Procedural and Anatomical Determinants of Multielectrode Renal Denervation Efficacy

Radiofrequency renal denervation is under investigation for treatment of hypertension with variable success. We developed preclinical models to examine the dependence of ablation biomarkers on renal denervation treatment parameters and anatomic variables. One hundred twenty-nine porcine renal arteries were denervated with an irrigated radiofrequency catheter with multiple helically arrayed electrodes. Nerve effects and ablation geometries at 7 days were characterized histomorphometrically and correlated with associated renal norepinephrine levels. Norepinephrine exhibited a threshold dependence on the percentage of affected nerves across the range of treatment durations (30-60 s) and power set points (6-20 W). For 15 W/30 s treatments, norepinephrine reduction and percentage of affected nerves tracked with number of electrode treatments, confirming additive effects of helically staggered ablations. Threshold effects were only attained when ≥4 electrodes were powered. Histomorphometry and computational modeling both illustrated that radiofrequency treatments directed at large neighboring veins resulted in subaverage ablation areas and, therefore, contributed suboptimally to efficacy. Account for measured nerve distribution patterns and the annular geometry of the artery revealed that, regardless of treatment variables, total ablation area and circumferential coverage were the prime determinants of renal denervation efficacy, with increased efficacy at smaller diameters.

Anatomical and procedural determinants of ambulatory blood pressure lowering following catheter-based renal denervation using radiofrequency

BACKGROUND/PURPOSE

Catheter-based renal sympathetic denervation (RDN) has been introduced to lower blood pressure (BP) and sympathetic activity in patients with uncontrolled hypertension with at best equivocal results. It has been postulated that anatomic and procedural elements introduce unaccounted variability and yet little is known of the impact of renal anatomy and procedural parameters on BP response to RDN.

METHODS/MATERIALS

Anatomical parameters such as length and diameter were analyzed by quantitative vascular analysis and the prevalence of accessory renal arteries and renal artery disease were documented in 150 patients with resistant hypertension undergoing bilateral RDN using a mono-electrode radiofrequency catheter (Symplicity Flex, Medtronic).

RESULTS

Accessory renal arteries and renal artery disease were present in 56 (37%) and 14 patients (9%), respectively. At 6-months, 24 h-ambulatory BP was reduced by 11/6 mm Hg (p < 0.001 for both). Change of systolic blood pressure (SBP) was not related to the presence of accessory renal arteries (p = 0.543) or renal artery disease (p = 0.598). Patients with at least one main renal artery diameter ≤ 4 mm had a more pronounced reduction of 24 h-ambulatory SBP compared to patients where both arteries were >4 mm (-19 vs. -10 mmHg; p = 0.038). Neither the length of the renal artery nor the number of RF ablations influenced 24 h-ambulatory BP reduction at 6 months.

CONCLUSIONS

24 h-ambulatory BP lowering was most pronounced in patients with smaller renal artery diameter but not related to renal artery length, accessory arteries or renal artery disease. Further, there was no dose-response relationship observed with increasing number of ablations.

CONDENSED ABSTRACT

Because little is known of the impact of renal anatomy and procedural parameters on blood pressure (BP) response to renal denervation (RDN), anatomical and procedural data were analyzed in 150 patients undergoing bilateral RDN. BP lowering was most pronounced in patients with smaller renal artery diameter but not related to renal artery length, the presence of renal artery disease or accessory renal arteries. Further, there was no dose-response relationship observed with increasing number of ablations.

Quantitative angiographic anatomy of the renal arteries and adjacent aorta in the swine for preclinical studies of intravascular catheterization devices

Swine are the most common animal model in preclinical studies of cardiovascular devices. Because of the recent trend for development of new devices for percutaneous catheterization, especially for the renal arteries (RAs), we examined the quantitative anatomical dimensions of the RAs and adjacent aorta in swine. Angiographic images were analyzed in 66 female Yorkshire/Landrace crossbred swine. The diameter of both the right and left main RA was 5.4 ± 0.6 mm. The length of the right main RA was significantly longer than that of the left (29.8 ± 7.5 mm vs. 20.6 ± 5.4 mm, respectively; P<0.001). The diameter of both the right and left branch RA with diameters ≥3 mm (the target vessel diameter of recently developed devices) was 3.8 ± 0.5 mm. The right branch RA was significantly longer than that of the left (18.9 ± 7.8 mm vs. 16.4 ± 7.4 mm, respectively; P<0.05). The branching angle of the right RA from the aorta was significantly smaller than that of the left (91 ± 12° vs. 103 ± 15°, respectively; P<0.001). The diameters of the suprarenal and infrarenal aorta were 10.6 ± 1.1 mm and 9.7 ± 0.9 mm, respectively. In conclusion, because of their similar dimensions to human, swine are an appropriate animal model for assessing the safety of, and determining optimal design of, catheter devices for RAs in simulated clinical use. However, there were species differences in the branching angle and adjacent aorta diameter, suggesting that swine models alone are inadequate to assess the delivery performance of catheter devices for RAs.