The uncertain value of renal artery interventions: where are we now?

Successful Treatment of Resistant Hypertension by Means of Chronic Renal Artery Occlusion Revascularization in a Fragile Patient

BACKGROUND

Renal artery stenosis is a common cause of secondary hypertension refractory to medical therapy. Percutaneous angioplasty along with metallic stent placement has been described as an effective treatment for revascularization of the renal artery.

CASE REPORT

A 54-year-old woman affected by paranoid schizophrenia with a history of hypertension and chronic renal failure due to renal artery occlusion was treated by endovascular recanalization and stent placement that resulted in improvement of renal function and control of hypertension. Laboratory studies 4 months after the revascularization revealed blood creatinine decrease gradually from 8.57 mg/dL to 3 mg/dL.

CONCLUSIONS

Revascularization with stenting has proven to be a safe and effective procedure in the treatment of total renal artery occlusion which also led to a significant relief at a psychological level.

Renal artery stenosis in patients with resistant hypertension

The aim of the study was to assess the significance of renal translesional pressure gradients in predicting improvement in resistant hypertension after stenting for moderate renal artery stenosis (RAS). In 37 patients with RAS and resistant hypertension subjected to renal stenting, translesional pressure gradients both at rest and hyperemic were measured using a pressure guidewire. Twenty-four-hour ambulatory blood pressure measurements were performed in all patients on admission and 3 months after the intervention. Angioplasty was successful in all patients, with reduction of artery diameter stenosis from 60 ± 12% to 10 ± 6% (p <0.0001). At 3 months, with maintained hypotensive agents (4.0 ± 1.4 vs 4.0 ± 1.6), significant reductions in systolic blood pressure (SBP) and diastolic blood pressure were noted (-5 and -2 mm Hg, respectively). In multivariate analysis, the mean baseline gradient (MBG) was the only independent predictor of improvement in SBP (regression coefficient 0.292; standard error 0.11; p value 0.014). In the receiver operating characteristic curve analysis, MBG had a larger area under the curve than other parameters, and the MBG >22 mm Hg had the highest sensitivity, specificity, and accuracy (50%, 95%, and 0.74%, respectively) in predicting hypertension improvement after stenting. In patients with MBG >22 mm Hg, SBP decreased by 12 versus 3 mm Hg (p <0.01) in patients with MBG ≤22 mm Hg, whereas diastolic blood pressure in both groups decreased by 3 versus 1 mm Hg, respectively (NS). In conclusion, MBG value of >22 mm Hg provides the highest accuracy in predicting hypertension improvement after stenting for moderate RAS in patients with resistant hypertension.

Prediction and assessment of responses to renal artery revascularization with dynamic contrast-enhanced magnetic resonance imaging: a pilot study

The aim of this study was to assess the potential of dynamic contrast-enhanced (DCE) MRI to predict and evaluate functional outcomes after renal artery revascularization for renal artery stenosis (RAS). The single-kidney glomerular filtration rate (SK-GFR) was measured in 15 patients with atherosclerotic RAS with DCE-MRI and radioisotopes at baseline and 4 mo after revascularization. DCE-MRI also produced measurements of blood flow, blood volume, extraction fraction, tubular transit time, and functional volume. Stented kidneys (n = 22) were divided into three response groups on the basis of the changes in radioisotope SK-GFR: improved (n = 5), stable (n = 13), and deteriorated (n = 4). A good agreement was found between SK-GFR values from DCE-MRI and radioisotopes (correlation coefficient: 0.91). Before intervention, kidneys that improved had lower extraction fraction, higher blood volume, longer tubular transit time, and lower SK-GFR. After intervention, improved kidneys had increased functional volume, and deteriorated kidneys had reduced functional volume and extraction fraction. Revascularization improved blood flow and blood volume in all groups. This pilot study led to the hypothesis that well-vascularized kidneys with reduced extraction fractions are most likely to benefit from revascularization. More generally, DCE-MRI has the potential to replace radioisotope measurement of SK-GFR and may improve patient management by providing additional information on tissue perfusion.

TGF expression and macrophage accumulation in atherosclerotic renal artery stenosis

BACKGROUND AND OBJECTIVES

Atherosclerotic renal artery stenosis (ARAS) reduces renal blood flow and is a potential cause of chronic kidney injury, yet little is known regarding inflammatory pathways in this disorder in human participants. This study aimed to examine the hypothesis that reduced renal blood flow (RBF) in ARAS would be associated with tissue TGF-β activation and inflammatory cell accumulation.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

This cross-sectional study of ARAS of varying severity compared transjugular biopsy specimens in patients with ARAS (n=12, recruited between 2008 and 2012) with tissue from healthy kidney donors (n=15) and nephrectomy specimens from individuals with total vascular occlusion (n=65). ARAS patients were studied under controlled conditions to measure RBF by multidetector computed tomography and tissue oxygenation by blood oxygen level-dependent magnetic resonance imaging.

RESULTS

Compared with the nonstenotic contralateral kidneys, RBF was reduced in poststenotic kidneys (242±149 versus 365+174 ml/min; P<0.01) as was single-kidney GFR (28±17 versus 41±19 ml/min; P<0.01), whereas cortical and medullary oxygenation were relatively preserved. Tissue TGF-β immunoreactivity was higher in ARAS patients compared with those with both normal kidneys and those with total occlusion (mean score 2.4±0.7 versus 1.5+1.1 in the nephrectomy group and versus 0±0 in donors; P<0.01). By contrast, the number of CD68+ macrophages was higher with greater disease severity (from 2.2±2.7 in normal to 22.4±18 cells/high-power field in nephrectomy samples; P<0.001).

CONCLUSIONS

The results of this study indicate robust stimulation of TGF-β associated with macrophage infiltration within the human kidney with vascular occlusive disease.

Percutaneous revascularization for ischemic nephropathy: the past, present, and future

Occlusion of the renal arteries can threaten the viability of the kidney when severe, in addition to accelerating hypertension and circulatory congestion. Renal artery stenting procedures have evolved from a treatment mainly for renovascular hypertension to a maneuver capable of recovering threatened renal function in patients with “ischemic nephropathy” and improving management of congestive heart failure. Improved catheter design and techniques have reduced, but not eliminated hazards associated with renovascular stenting. Expanded use of endovascular stent grafts to treat abdominal aortic aneurysms has introduced a new indication for renal artery stenting to protect the renal circulation when grafts cross the origins of the renal arteries. Although controversial, prospective randomized trials to evaluate the added benefit of revascularization to current medical therapy for atherosclerotic renal artery stenosis until now have failed to identify major benefits regarding either renal function or blood pressure control. These studies have been limited by selection bias and have been harshly criticized. While studies of tissue oxygenation using blood oxygen level dependent (BOLD) MR establish that kidneys can adapt to reduced blood flow to some degree, more severe occlusive disease leads to cortical hypoxia associated with microvascular rarefication, inflammatory injury and fibrosis. Current research is directed toward identifying pathways of irreversible kidney injury due to vascular occlusion and to increase the potential for renal repair after restoring renal artery patency. The role of nephrologists likely will focus upon recognizing the limits of renal adaptation to vascular disease and identifying kidneys truly at risk for ischemic injury at a time point when renal revascularization can still be of benefit to recovering kidney function.

Clinical effect of endovascular treatment on blood pressure and kidney function for hypertensive patients with renal artery stenosis

The objective of this study was to evaluate the clinical effect of endovascular treatment on postoperative blood pressure (BP) control and kidney function of hypertensive patients with renal artery stenosis (RAS). Between January 2004 and December 2011, RAS was diagnosed in 120 renal arteries from 115 hypertensive patients. Preoperative and postoperative BPs and glomerular filtration rate (GFR) were monitored. Postoperative oral antiplatelet and antihypertensive agents were administered. Clinical follow-up was available for all patients for at least 6 months. Balloon angioplasty was performed successfully in 110 patients, and stents were deployed in 94 renal arteries from 89 patients. Hypertension was cured and lessened in 19 and 61 patients, respectively. Blood pressure was stable and worsened in 26 and 9 patients, respectively. The renal function was improved and stable in 23 patients and 57 patients, respectively. Deterioration of renal function was observed in 11 patients. Doppler ultrasound after discharge revealed 87 patent renal arteries and fixed stents in 82 patients 6 months after procedure. Balloon angioplasty and stent deployment are effective and feasible procedures for patients with RAS that help in controlling BP and improving renal function moderately.

The effect of revascularization of renal artery stenosis on renal perfusion in patients with atherosclerotic renovascular disease

BACKGROUND

Only a small fraction of patients with atherosclerotic renovascular disease (ARVD) treated with revascularization have improved renal function after the procedure. It has been suggested that this may be due to effects of renal microvascular disease. Our aim was to measure the effect of renal artery stenosis (RAS) revascularization on renal perfusion in patients with renovascular disease.

METHODS

Seventeen renovascular disease patients were treated by dilatation of unilateral (N = 8) or bilateral (N = 9) RAS (N = 23 kidneys), mainly because of uncontrolled or refractory hypertension. The patients were studied before and after (103 ± 29 days) the procedure. Renal perfusion was measured using quantitative positron emission tomography (PET) perfusion imaging.

RESULTS

Although renal perfusion correlated inversely with the degree of RAS in patients with renovascular disease, it did not change after revascularization.

CONCLUSIONS

Our data support the notion of former clinical trials that angiographic severity of RAS does not determine the response to revascularization. Quantitative PET perfusion imaging is a promising tool to noninvasively measure renal perfusion for the assessment of physiological impact of RAS.

Addition of endothelial progenitor cells to renal revascularization restores medullary tubular oxygen consumption in swine renal artery stenosis

Renal artery stenosis (RAS) promotes microvascular rarefaction and fibrogenesis, which may eventuate in irreversible kidney injury. We have shown that percutaneous transluminal renal angioplasty (PTRA) or endothelial progenitor cells (EPC) improve renal cortical hemodynamics and function in the poststenotic kidney. The renal medulla is particularly sensitive to hypoxia, yet little is known about reversibility of medullary injury on restoration of renal blood flow. This study was designed to test the hypothesis that PTRA, with or without adjunct EPC delivery to the stenotic kidney, may improve medullary remodeling and tubular function. RAS was induced in 21 pigs using implantation of irritant coils, while another group served as normal controls (n = 7 each). Two RAS groups were then treated 6 wk later with PTRA or both PTRA and EPC. Four weeks later, medullary hemodynamics, microvascular architecture, and oxygen-dependent tubular function of the stenotic kidneys were examined using multidetector computed tomography, microcomputed tomography, and blood oxygenation level-dependent MRI, respectively. Medullary protein expression of vascular endothelial growth factor, endothelial nitric oxide synthase, hypoxia-inducible factor-1α, and NAD(P)H oxidase p47 were determined. All RAS groups showed decreased medullary vascular density and blood flow. However, in RAS+PTRA+EPC animals, EPC were engrafted in tubular structures, oxygen-dependent tubular function was normalized, and fibrosis attenuated, despite elevated expression of hypoxia-inducible factor-1α and sustained downregulation of vascular endothelial growth factor. In conclusion, EPC delivery, in addition to PTRA, restores medullary oxygen-dependent tubular function, despite impaired medullary blood and oxygen supply. These results support further development of cell-based therapy as an adjunct to revascularization of RAS.

Objective performance goals of safety and blood pressure efficacy for clinical trials of renal artery bare metal stents in hypertensive patients with atherosclerotic renal artery stenosis

OBJECTIVE

To provide safety and performance goals for prospective single-arm trials of bare metal renal artery stenting in patients with resistant hypertension associated with high grade atherosclerotic renal artery stenosis.

BACKGROUND

To date, there have been no US Pre-Market Approval (PMA) bare metal renal stent device trials which have focused on improvement of blood pressure control as a primary effectiveness endpoint.

METHODS

Analysis of subject-level data from three large industry sponsored pre-market approval (PMA) trials was performed. Hypertensive patients (≥ 155 mmHg) with a ≥ 50% atherosclerotic renal artery stenosis were included. Thirty day and 9-month systolic and diastolic blood pressure measurements, renal function and 9-month duplex ultrasound assessment of renal artery patency were analyzed.

RESULTS

Initial data analysis of 600 patients from the 3 PMA trials identified 286 patients who met inclusion criteria. The mean baseline systolic blood pressure was 177.8 ± 19.3 mmHg with a mean 68.1% diameter renal artery stenosis. Nine months after successful stenting, the mean SBP was 156.7 ± 24.1 mmHg; the 9 month restenosis rate was 14.4%.

CONCLUSION

Based on the statistical modeling of these data and a priori established performance criteria, the co-primary endpoints of 9 month reduction in blood pressure and in-stent restenosis are proposed. The reduction in blood pressure will be analyzed as a continuous variable and will be compared to this performance goal.

Clinical outcomes after percutaneous revascularization versus medical management in patients with significant renal artery stenosis: a meta-analysis of randomized controlled trials

BACKGROUND

We sought to systematically evaluate whether percutaneous revascularization is associated with additional clinical benefit in patients with renal artery stenosis (RAS) as compared with medical management alone.

METHODS

We included randomized controlled trials that compared percutaneous revascularization in addition to medical therapy versus medical management alone in patients with RAS. Six trials with 1,208 patients were included.

RESULTS

At a mean follow-up of 29 months, there was no change in systolic blood pressure (weighted mean difference [WMD] = 1.20 mm Hg, 95% CI -1.18 to 3.58 mm Hg) or diastolic blood pressure (WMD = -1.60 mm Hg, 95% CI -4.22 to 1.02 mm Hg) from baseline in the percutaneous revascularization arm compared with the medical management arm. There was a reduction in the mean number of antihypertensive medications (WMD = -0.26, 95% CI -0.39 to -0.13, P < .001), but not serum creatinine (WMD = -0.14 mg/dL, 95% CI -0.29 to 0.007 mg/dL), in the percutaneous revascularization arm at the end of follow-up. Percutaneous revascularization was not associated with a significant difference in all-cause mortality (relative risk [RR] = 0.96, 95% CI 0.74-1.25), congestive heart failure (RR = 0.79, 95% CI 0.56-1.13), stroke (RR = 0.86, 95% CI 0.50-1.47), or worsening renal function (RR = 0.91, 95% CI 0.67-1.23) as compared with medical management.

CONCLUSIONS

In patients with RAS, percutaneous renal revascularization in addition to medical therapy may result in a lower requirement for antihypertensive medications, but not with improvements in serum creatinine or clinical outcomes, as compared with medical management over an intermediate period of follow-up. Further studies are needed to identify the appropriate patient population most likely to benefit from its use.

Renovascular disease, microcirculation, and the progression of renal injury: role of angiogenesis

Emerging evidence supports the pivotal role of renal microvascular disease as a determinant of tubulo-interstitial and glomerular fibrosis in chronic kidney disease. An intact microcirculation is vital to restore blood flow to the injured tissues, which is a crucial step to achieve a successful repair response. The purpose of this review is to discuss the impact and mechanisms of the functional and structural changes of the renal microvascular network, as well as the role of these changes in the progression and irreversibility of renal injury. Damage of the renal microcirculation and deterioration of the angiogenic response may constitute early steps in the complex pathways involved in progressive renal injury. There is limited but provocative evidence that stimulation of vascular proliferation and repair may stabilize renal function and slow the progression of renal disease. The feasibility of novel potential therapeutic interventions for stabilizing the renal microvasculature is also discussed. Targeted interventions to enhance endogenous renoprotective mechanisms focused on the microcirculation, such as cell-based therapy or the use of angiogenic cytokines have shown promising results in some experimental and clinical settings.

Translesional Pressure Gradients to Predict Blood Pressure Response After Renal Artery Stenting in Patients With Renovascular Hypertension

Background—

In previous studies on the effect of renal stenting on arterial hypertension, patients were selected mainly on the basis of angiographic parameters of the renal artery stenosis. The aim of the present study was to evaluate whether translesional pressure gradients could identify the patients with renal artery stenosis who might benefit from stenting.

Methods and Results—

A total of 53 consecutive hypertensive patients with unilateral RAS scheduled for renal artery intervention were recruited. Transstenotic pressure gradients were measured at baseline and during maximal hyperemia, before renal artery stenting. Twenty-four-hour ambulatory blood pressure measurements were performed in all patients before and 3 months after the intervention. Average reductions in systolic blood pressure and diastolic blood pressure at follow-up were −20±30 mm Hg and −2±12 mm Hg, respectively. At multivariate analysis, dopamine-induced mean gradient was the only independent predictor of the variations of both systolic blood pressure (regression coefficient=−4.03, standard error=1.11; P <0.001) and diastolic blood pressure (regression coefficient=−3.11, standard error=1.20; P =0.009). Patients who showed a decline in systolic blood pressure from the baseline value >20 mm Hg were considered as “responders.” The optimal cutoff for identification of “responders” was a dopamine-induced mean gradient ≥20 mm Hg (area under the curve, 0.77; 95% confidence interval, 0.64 to 0.90; P =0.001).

Conclusions—

A dopamine-induced mean pressure gradient of ≥20 mm Hg is highly predictive of arterial hypertension improvement after renal stenting, and therefore this measurement is useful for appropriate selection of patients with arterial hypertension.

Renovascular hypertension and ischemic nephropathy

Renovascular disease remains among the most prevalent and important causes of secondary hypertension and renal dysfunction. Many lesions reduce perfusion pressure including fibromuscular diseases and renal infarction, but most are caused by atherosclerotic disease. Epidemiologic studies establish a strong association between atherosclerotic renal-artery stenosis (ARAS) and cardiovascular risk. Hypertension develops in patients with renovascular disease from a complex set of pressor signals, including activation of the renin-angiotensin system (RAS), recruitment of oxidative stress pathways, and sympathoadrenergic activation. Although the kidney maintains function over a broad range of autoregulation, sustained reduction in renal perfusion leads to disturbed microvascular function, vascular rarefaction, and ultimately development of interstitial fibrosis. Advances in antihypertensive drug therapy and intensive risk factor management including smoking cessation and statin therapy can provide excellent blood pressure control for many individuals. Despite extensive observational experience with renal revascularization in patients with renovascular hypertension, recent prospective randomized trials fail to establish compelling benefits either with endovascular stents or with surgery when added to effective medical therapy. These trials are limited and exclude many patients most likely to benefit from revascularization. Meaningful recovery of kidney function after revascularization is limited once fibrosis is established. Recent experimental studies indicate that mechanisms allowing repair and regeneration of parenchymal kidney tissue may lead to improved outcomes in the future. Until additional staging tools become available, clinicians will be forced to individualize therapy carefully to optimize the potential benefits regarding both blood pressure and renal function for such patients.

Renal microvascular disease determines the responses to revascularization in experimental renovascular disease

BACKGROUND

Percutaneous transluminal renal angioplasty (PTRA) is the most frequent therapeutic approach to resolving renal artery stenosis (RAS). However, renal function recovers in only 30% of the cases. The causes of these poor outcomes are still unknown. We hypothesized that preserving the renal microcirculation distal to RAS will improve the responses to PTRA.

METHODS AND RESULTS

RAS was induced in 28 pigs. In 14, vascular endothelial growth factor (VEGF)-165 0.05 microg/kg was infused intrarenally (RAS+VEGF). Single-kidney function was assessed in all pigs in vivo using ultrafast CT after 6 weeks. Observation of half of the RAS and RAS+VEGF pigs was completed. The other half underwent PTRA and repeated VEGF, and CT studies were repeated 4 weeks later. Pigs were then euthanized, the stenotic kidney removed, renal microvascular (MV) architecture reconstructed ex vivo using 3D micro-CT, and renal fibrosis quantified. The degree of RAS and hypertension were similar in RAS and RAS+VEGF. Renal function and MV density were decreased in RAS but improved in RAS+VEGF. PTRA largely resolved RAS, but the improvements of hypertension and renal function were greater in RAS+VEGF+PTRA than in RAS+PTRA, accompanied by a 34% increase in MV density and decreased fibrosis.

CONCLUSIONS

Preservation of the MV architecture and function in the stenotic kidney improved the responses to PTRA, indicating that renal MV integrity plays a role in determining the responses to PTRA. This study indicates that damage and early loss of renal MV is an important determinant of the progression of renal injury in RAS and instigates often irreversible damage.

Revascularization of swine renal artery stenosis improves renal function but not the changes in vascular structure

Renal revascularization by percutaneous transluminal angioplasty improves blood pressure and stenotic kidney function in selected groups of patients, but the reversibility of intrarenal and microvascular remodeling remains unknown. Here, we tested the hypothesis that renal angioplasty improves the function and structure of renal microcirculation in experimental chronic renal artery stenosis. Stenotic kidney function, hemodynamics, and endothelial function were assessed in vivo in pigs after 10 weeks of unilateral renal artery stenosis. Renal microvascular remodeling, angiogenic pathways, and fibrosis were measured ex vivo. Angioplasty and stenting carried out 4 weeks before measurement decreased blood pressure, improved glomerular filtration rate, and improved microvascular endothelial function. It also promoted the expression of angiogenic factors and decreased renal apoptosis due to stenosis, compared with a sham intervention. The spatial density of renal microvessels, however, was partially improved after angioplasty. Renal blood flow was incompletely restored compared with the kidneys of sham-treated animals, as was interstitial fibrosis. Renal microvascular media-to-lumen ratio remained unchanged by angioplasty. Thus, our study shows that revascularization of a stenotic renal artery restores the glomerular filtration rate and renal endothelial function 4 weeks later. Renal hemodynamics and structure, however, are incompletely resolved.

Impact of baseline renal function on outcomes of renal artery stenting in hypertensive patients

Renal artery stenting may improve blood pressure (BP) and renal function in resistant hypertension patients; however, benefit may differ depending on the degree of renal dysfunction. The authors analyzed 67 consecutive patients receiving stenting for obstructive renal artery disease between 2002 and 2005. Patients were categorized as normal or mildly impaired according to estimated glomerular filtration rate (eGFR) (> or =60 mL/min/1.73 m(2)), moderately impaired (eGFR 30 to 59 mL/min/1.73 m(2)), and severely impaired (eGFR <30 mL/min/1.73 m(2)). In patients with eGFR > or =60, systolic BP did not significantly improve from baseline. However, in patients with an eGFR between 30 and 59 mL/min/1.73 m(2), systolic BP decreased by 12 mm Hg at 6 months (P=.02) and 14 mm Hg at 12 months (P=.01). Greater benefit was observed in patients with eGFR <30 mL/min/1.73 m(2), with a 16 mm Hg (P=.10) and 21 mm Hg (P=.02) decrease at 6 and 12 months, respectively. Renal function was stable across all groups. Renal artery stenting reduced BP and produced greatest benefit in patients with baseline impaired renal function.

Timing and selection for renal revascularization in an era of negative trials: what to do?

Management of atherosclerotic renal artery stenosis has become more complex with advances in both medical therapy and endovascular procedures. Results from recent trials fail to demonstrate major benefits of endovascular stenting in addition to optimal medical therapy. The general applicability of these results to many patients is limited by short-term follow-up and selection biases in recruitment. Many patients at highest risk were excluded from these studies and some were included with trivial lesions. Identification of patients with hemodynamically significant lesions remains a challenge and has led to more stringent criteria for Doppler ultrasound, measurement of translesional gradients and quantitative angiography. Although many patients can now be managed with medical therapy, it should be recognized that long-term reduction in antihypertensive drug requirements and recovery of kidney function are limited to those undergoing renal revascularization. As with any major vascular lesion, follow-up for disease stability and/or progression is essential. The ambiguity of present trial data may lead some to overlook selected subgroups that would benefit from restoring renal blood supply through revascularization. Further studies to more precisely identify kidneys that can recover function and/or are beyond meaningful recovery are essential. Considering the comorbid risks for the atherosclerotic population, it will remain imperative for clinicians to consider the hazards, costs and benefits carefully for each patient to determine the role and timing for both medical therapy and revascularization.