The Cardiovascular Outcomes with Renal Atherosclerotic Lesions (CORAL) study: rationale and methods

Anemia and Hypoxia Impact on Chronic Kidney Disease Onset and Progression: Review and Updates

Chronic kidney disease (CKD) is caused by hypoxia in the renal tissue, leading to inflammation and increased migration of pathogenic cells. Studies showed that leukocytes directly sense hypoxia and respond by initiating gene transcription, encoding the 2-integrin adhesion molecules. Moreover, other mechanisms participate in hypoxia, including anemia. CKD-associated anemia is common, which induces and worsens hypoxia, contributing to CKD progression. Anemia correction can slow CKD progression, but it should be cautiously approached. In this comprehensive review, the underlying pathophysiology mechanisms and the impact of renal tissue hypoxia and anemia in CKD onset and progression will be reviewed and discussed in detail. Searching for the latest updates in PubMed Central, Medline, PubMed database, Google Scholar, and Google search engines were conducted for original studies, including cross-sectional studies, cohort studies, clinical trials, and review articles using different keywords, phrases, and texts such as "CKD progression, anemia in CKD, CKD, anemia effect on CKD progression, anemia effect on CKD progression, and hypoxia and CKD progression". Kidney tissue hypoxia and anemia have an impact on CKD onset and progression. Hypoxia causes nephron cell death, enhancing fibrosis by increasing interstitium protein deposition, inflammatory cell activation, and apoptosis. Severe anemia correction improves life quality and may delay CKD progression. Detection and avoidance of the risk factors of hypoxia prevent recurrent acute kidney injury (AKI) and reduce the CKD rate. A better understanding of kidney hypoxia would prevent AKI and CKD and lead to new therapeutic strategies.

Peristenotic Collateral Circulation in Atherosclerotic Renovascular Disease: Association With Kidney Function and Response to Treatment

The significance of peristenotic collateral circulation (PCC) development around a stenotic renal artery is unknown. We tested the hypothesis that PCC is linked to loss of kidney function and recovery potential in patients with atherosclerotic renovascular disease (ARVD). Thirty-four patients with ARVD were assigned to medical-therapy with or without revascularization based on clinical indications. The PCC was visualized using multidetector computed tomography and defined relative to segmental arteries in patients with essential hypertension. PCC number before and 3 months after treatment was correlated with various renal parameters. Thirty-four stenotic kidneys from 30 patients were analyzed. PCC number correlated inversely with kidney volume. ARVD-stenotic kidneys with baseline PCC (collateral ARVD [C-ARVD], n=13) associated with elevated 24-hour urine protein and stenotic kidney vein level of tumor necrosis factor-α, lower single-kidney volume and blood flow, and greater hypoxia than in stenotic kidneys with no PCC (no collateral ARVD [NC-ARVD], n=17). Revascularization (but not medical-therapy alone) improved stenotic kidney function and reduced inflammation in both NC-ARVD and C-ARVD. In C-ARVD, revascularization also increased stenotic kidney volume, blood flow, and oxygenation to levels comparable to NC-ARVD, and induced PCC regression. However, revascularization improved systolic blood pressure, plasma renin activity, and filtration fraction only in NC-ARVD. Therefore, patients with C-ARVD have greater kidney dysfunction, atrophy, hypoxia, and inflammation compared with patients with NC-ARVD, suggesting that PCC does not effectively protect the stenotic kidney in ARVD. Renal artery revascularization improved in C-ARVD stenotic kidney function, but not hypertension or renin-angiotensin system activation. These observations may help direct management of patients with ARVD.

Cohort profile: The MULTI sTUdy Diabetes rEsearch (MULTITUDE) consortium

PURPOSE

Globally, the age-standardised prevalence of type 2 diabetes mellitus (T2DM) has nearly doubled from 1980 to 2014, rising from 4.7% to 8.5% with an estimated 422 million adults living with the chronic disease. The MULTI sTUdy Diabetes rEsearch (MULTITUDE) consortium was recently established to harmonise data from 17 independent cohort studies and clinical trials and to facilitate a better understanding of the determinants, risk factors and outcomes associated with T2DM.

PARTICIPANTS

Participants range in age from 3 to 88 years at baseline, including both individuals with and without T2DM. MULTITUDE is an individual-level pooled database of demographics, comorbidities, relevant medications, clinical laboratory values, cardiac health measures, and T2DM-associated events and outcomes across 45 US states and the District of Columbia.

FINDINGS TO DATE

Among the 135 156 ongoing participants included in the consortium, almost 25% (33 421) were diagnosed with T2DM at baseline. The average age of the participants was 54.3, while the average age of participants with diabetes was 64.2. Men (55.3%) and women (44.6%) were almost equally represented across the consortium. Non-whites accounted for 31.6% of the total participants and 40% of those diagnosed with T2DM. Fewer individuals with diabetes reported being regular smokers than their non-diabetic counterparts (40.3% vs 47.4%). Over 85% of those with diabetes were reported as either overweight or obese at baseline, compared with 60.7% of those without T2DM. We observed differences in all-cause mortality, overall and by T2DM status, between cohorts.

FUTURE PLANS

Given the wide variation in demographics and all-cause mortality in the cohorts, MULTITUDE consortium will be a unique resource for conducting research to determine: differences in the incidence and progression of T2DM; sequence of events or biomarkers prior to T2DM diagnosis; disease progression from T2DM to disease-related outcomes, complications and premature mortality; and to assess race/ethnicity differences in the above associations.

Atherosclerotic renal artery stenosis is associated with elevated cell cycle arrest markers related to reduced renal blood flow and postcontrast hypoxia

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) reduces renal blood flow (RBF), ultimately leading to kidney hypoxia and inflammation. Insulin-like growth factor binding protein-7 (IGFBP-7) and tissue inhibitor of metalloproteinases-2 (TIMP-2) are biomarkers of cell cycle arrest, often increased in ischemic conditions and predictive of acute kidney injury (AKI). This study sought to examine the relationships between renal vein levels of IGFBP-7, TIMP-2, reductions in RBF and postcontrast hypoxia as measured by blood oxygen level-dependent (BOLD) magnetic resonance imaging.

METHODS

Renal vein levels of IGFBP-7 and TIMP-2 were obtained in an ARAS cohort (n= 29) scheduled for renal artery stenting and essential hypertensive (EH) healthy controls (n = 32). Cortical and medullary RBFs were measured by multidetector computed tomography (CT) immediately before renal artery stenting and 3 months later. BOLD imaging was performed before and 3 months after stenting in all patients, and a subgroup (N = 12) underwent repeat BOLD imaging 24 h after CT/stenting to examine postcontrast/procedure levels of hypoxia.

RESULTS

Preintervention IGFBP-7 and TIMP-2 levels were elevated in ARAS compared with EH (18.5 ± 2.0 versus 15.7 ± 1.5 and 97.4 ± 23.1 versus 62.7 ± 9.2 ng/mL, respectively; P< 0.0001); baseline IGFBP-7 correlated inversely with hypoxia developing 24 h after contrast injection (r = -0.73, P< 0.0001) and with prestent cortical blood flow (r = -0.59, P= 0.004).

CONCLUSION

These data demonstrate elevated IGFBP-7 and TIMP-2 levels in ARAS as a function of the degree of reduced RBF. Elevated baseline IGFBP-7 levels were associated with protection against postimaging hypoxia, consistent with 'ischemic preconditioning'. Despite contrast injection and stenting, AKI in these high-risk ARAS subjects with elevated IGFBP-7/TIMP-2 was rare and did not affect long-term kidney function.

Urinary Mitochondrial DNA Copy Number Identifies Chronic Renal Injury in Hypertensive Patients

Mitochondrial injury contributes to renal dysfunction in several models of renal disease, but its involvement in human hypertension remains unknown. Fragments of the mitochondrial genome released from dying cells are considered surrogate markers of mitochondrial injury. We hypothesized that hypertension would be associated with increased urine mitochondrial DNA (mtDNA) copy numbers. We prospectively measured systemic and urinary copy number of the mtDNA genes cytochrome-c oxidase-3 and NADH dehydrogenase subunit-1 by quantitative polymerase chain reaction in essential (n=25) and renovascular (RVH, n=34) hypertensive patients and compared them with healthy volunteers (n=22). Urinary kidney injury molecule-1 and neutrophil gelatinase-associated lipocalin served as indices of renal injury. Renal blood flow and oxygenation were assessed by multidetector computed tomography and blood oxygen level-dependent magnetic resonance imaging. Blood pressure, urinary neutrophil gelatinase-associated lipocalin, and kidney injury molecule-1 were similarly elevated in essential hypertension and RVH, and estimated glomerular filtration rate was lower in RVH versus healthy volunteers and essential hypertension. Renal blood flow was lower in RVH compared with essential hypertension. Urinary mtDNA copy number was higher in hypertension compared with healthy volunteers, directly correlated with urinary neutrophil gelatinase-associated lipocalin and kidney injury molecule-1 and inversely with estimated glomerular filtration rate. In RVH, urinary mtDNA copy number correlated directly with intrarenal hypoxia. Furthermore, in an additional validation cohort, urinary mtDNA copy number was higher in RVH compared with healthy volunteers (n=10 each). The change in serum creatinine levels and estimated glomerular filtration rate 3 months after medical therapy without or with revascularization correlated with the change in urinary mtDNA. Therefore, elevated urinary mtDNA copy numbers in hypertensive patients correlated with markers of renal injury and dysfunction, implicating mitochondrial injury in kidney damage in human hypertension.

Hypoxia: The Force that Drives Chronic Kidney Disease

In the United States the prevalence of end-stage renal disease (ESRD) reached epidemic proportions in 2012 with over 600,000 patients being treated. The rates of ESRD among the elderly are disproportionally high. Consequently, as life expectancy increases and the baby-boom generation reaches retirement age, the already heavy burden imposed by ESRD on the US health care system is set to increase dramatically. ESRD represents the terminal stage of chronic kidney disease (CKD). A large body of evidence indicating that CKD is driven by renal tissue hypoxia has led to the development of therapeutic strategies that increase kidney oxygenation and the contention that chronic hypoxia is the final common pathway to end-stage renal failure. Numerous studies have demonstrated that one of the most potent means by which hypoxic conditions within the kidney produce CKD is by inducing a sustained inflammatory attack by infiltrating leukocytes. Indispensable to this attack is the acquisition by leukocytes of an adhesive phenotype. It was thought that this process resulted exclusively from leukocytes responding to cytokines released from ischemic renal endothelium. However, recently it has been demonstrated that leukocytes also become activated independent of the hypoxic response of endothelial cells. It was found that this endothelium-independent mechanism involves leukocytes directly sensing hypoxia and responding by transcriptional induction of the genes that encode the β2-integrin family of adhesion molecules. This induction likely maintains the long-term inflammation by which hypoxia drives the pathogenesis of CKD. Consequently, targeting these transcriptional mechanisms would appear to represent a promising new therapeutic strategy.

Changes in inflammatory biomarkers after renal revascularization in atherosclerotic renal artery stenosis

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) activates oxidative stress and chronic inflammatory injury. Contrast imaging and endovascular stenting pose potential hazards for acute kidney injury, particularly when superimposed upon reduced kidney perfusion.

METHODS

We measured sequential early and long-term changes in circulating inflammatory and injury biomarkers in 12 ARAS subjects subjected to computed tomography imaging and stent revascularization compared with essential hypertensive (EH) subjects of similar age under fixed sodium intake and medication regimens in a clinical research unit.

RESULTS

NGAL, TIMP-2, IGFBP7, MCP-1 and TNF-α all were elevated before intervention. Post-stenotic kidney volume, perfusion, blood flow and glomerular filtration rate (GFR) were lower in ARAS than in EH subjects. TIMP-2 and IGFBP7 fell briefly, then rose over 18 h after contrast imaging and stent deployment. Circulating NGAL decreased and remained lower for 27 h. These biomarkers in ARAS returned to baseline after 3 months, while kidney volume, perfusion, blood flow and GFR increased, but remained lower than EH.

CONCLUSIONS

These divergent patterns of inflammatory signals are consistent with cell cycle arrest (TIMP-2, IGFBP7) and relative protection from acute kidney injury after imaging and stenting. Sustained basal elevation of circulating and renal venous inflammatory biomarkers support ongoing, possibly episodic, renal stress in ARAS that limits toxicity from stent revascularization.

Differences in GFR and Tissue Oxygenation, and Interactions between Stenotic and Contralateral Kidneys in Unilateral Atherosclerotic Renovascular Disease

BACKGROUND AND OBJECTIVES

Atherosclerotic renal artery stenosis (ARAS) can reduce renal blood flow, tissue oxygenation, and GFR. In this study, we sought to examine associations between renal hemodynamics and tissue oxygenation with single-kidney function, pressor hormones, and inflammatory biomarkers in patients with unilateral ARAS undergoing medical therapy alone or stent revascularization.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Nonrandomized inpatient studies were performed in patients with unilateral ARAS (>60% occlusion) before and 3 months after revascularization (n=10) or medical therapy (n=20) or patients with essential hypertension (n=32) under identical conditions. The primary study outcome was change in single-kidney GFR. Individual kidney hemodynamics and volume were measured using multidetector computed tomography. Tissue oxygenation (using R(2)* as a measure of deoxyhemoglobin) was determined by blood oxygen level-dependent magnetic resonance imaging at 3 T. Renal vein neutrophil gelatinase-associated lipocalin (NGAL), monocyte chemoattractant protein-1 (MCP-1), and plasma renin activity were measured.

RESULTS

Total GFR did not change over 3 months in either group, but the stenotic kidney (STK) GFR rose over time in the stent compared with the medical group (+2.2[-1.8 to 10.5] versus -5.3[-7.3 to -0.3] ml/min; P=0.03). Contralateral kidney (CLK) GFR declined in the stent group (43.6±19.7 to 36.6±19.5 ml/min; P=0.03). Fractional tissue hypoxia fell in the STK (fraction R(2)* >30/s: 22.1%±20% versus 14.9%±18.3%; P<0.01) after stenting. Renal vein biomarkers correlated with the degree of hypoxia in the STK: NGAL(r=0.3; P=0.01) and MCP-1(r=0.3; P=0.02; more so after stenting). Renal vein NGAL was inversely related to renal blood flow in the STK (r=-0.65; P<0.001). Biomarkers were highly correlated between STK and CLK, NGAL (r=0.94; P<0.001), and MCP-1 (r=0.96; P<0.001).

CONCLUSIONS

These results showed changes over time in single-kidney GFR that were not evident in parameters of total GFR. Furthermore, they delineate the relationship of measurable tissue hypoxia within the STK and markers of inflammation in human ARAS. Renal vein NGAL and MCP-1 indicated persistent interactions between the ischemic kidney and both CLK and systemic levels of inflammatory cytokines.

Extrarenal atherosclerotic disease blunts renal recovery in patients with renovascular hypertension

BACKGROUND

Atherosclerotic renovascular disease (ARVD) is associated with high rates of coronary events and predicts mortality among patients with coronary artery disease (CAD). However, the impact of coronary atherosclerosis on renal outcomes after revascularization of ARVD is unclear. We hypothesized that CAD negatively impacts renal functional outcomes among patients with ARVD undergoing renal artery revascularization.

METHODS

Patients with ARVD who underwent echocardiography at Mayo Clinic, Rochester, Minnesota, USA between 2004 and 2012 were identified retrospectively and included if they had ejection fraction more than 50%. Renal and overall outcomes were compared among atherosclerotic renovascular disease patients with coronary artery disease (ARVD-C, n = 75) and without coronary artery disease (ARVD, n = 56), within 1 year from initial revascularization and included blood pressure control, renal function, and incident cardiovascular/cerebrovascular events.

RESULTS

Degree of renal artery stenosis was similar in both groups. ARVD-C had higher prevalence of diabetes, peripheral artery disease (PAD), and cerebrovascular disease, and lower baseline renal function. Risk of developing end-stage renal disease was higher in ARVD-C (11 vs. 2%, P = 0.05). Despite better control of blood pressure and cholesterol levels, renal function postrevascularization worsened in 15% of ARVD-C compared with 2% of ARVD (P = 0.01). Differences in clinical outcomes remained statistically significant after adjustment for covariables, including sex, baseline blood pressure, renal function, underlying diabetes, cholesterol levels, and medications. Similar differences in clinical outcomes were also associated with PAD and cerebrovascular disease.

CONCLUSION

CAD in patients with ARVD is a predictor of worse outcomes after renal revascularization, likely reflecting diffuse atherosclerotic disease. Further studies are needed to develop strategies to manage patients with vascular comorbidities and improve their outcomes.

Balloon angioplasty, with and without stenting, versus medical therapy for hypertensive patients with renal artery stenosis

BACKGROUND

Atherosclerotic renal artery stenosis is the most common cause of secondary hypertension. Balloon angioplasty with stenting is widely used for the treatment of hypertensive patients with renal artery stenosis but the effectiveness of this procedure in treating hypertension, improving renal function and preventing adverse cardiovascular and renal events remains uncertain. This is an update, to include the results of recent, important large trials, of a review first published in 2003.

OBJECTIVES

To compare the effectiveness of balloon angioplasty (with and without stenting) with medical therapy for the treatment of atherosclerotic renal artery stenosis in patients with hypertension. The following outcomes were compared: blood pressure control, renal function, frequency of cardiovascular and renal adverse events, presence or absence of restenosis of the renal artery, side effects of medical therapy, numbers and defined daily doses of antihypertensive drugs.

SEARCH METHODS

For this update the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched May 2014) and CENTRAL (2014, Issue 4). Bibliographies were also reviewed and trial authors were contacted for more information.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing balloon angioplasty with medical therapy in hypertensive patients with haemodynamically significant renal artery stenosis (greater than 50% reduction in luminal diameter) and with a minimum follow-up of six months.

DATA COLLECTION AND ANALYSIS

Data were extracted independently on trial design, participants, interventions and outcome measures. A formal meta-analysis was completed to assess the effect on blood pressure, renal function and cardiovascular and renal adverse events. Peto's odds ratios (ORs) and corresponding 95% confidence intervals (CI) for dichotomous outcomes and mean differences (MD) and corresponding 95% CIs for continuous variables were calculated.

MAIN RESULTS

Eight RCTs involving 2222 participants with renal artery stenosis were included in the review. The overall quality of evidence included in this review was moderate. Limited pooling of results was possible due to the variable presentation of some of the trial outcomes. Meta-analysis of the four studies reporting change in diastolic blood pressure (BP) found a small improvement in diastolic BP in the angioplasty group (MD -2.00 mmHg; 95% CI -3.72 to -0.27) whilst the meta-analysis of the five studies reporting change in systolic BP did not find any evidence of significant improvement (MD -1.07 mmHg; 95% CI -3.45 to 1.30). There was no significant effect on renal function as measured by serum creatinine (MD -7.99 µmol/L; 95% CI -22.6 to 6.62). Meta-analysis of the three studies that reported the mean number of antihypertensive drugs found a small decrease in antihypertensive drug requirements for the angioplasty group (MD -0.18; 95% CI -0.34 to -0.03). Repeat angiography was only performed on a small number of participants in a single trial and it was therefore not possible to comment on restenosis of the renal artery following balloon angioplasty. Based on the results of the seven studies that reported cardiovascular and renal clinical outcomes there were no differences in cardiovascular (OR 0.91; 95% CI 0.75 to 1.11) or renal adverse events (OR 1.02; 95% CI 0.75 to 1.38) between the angioplasty and medical treatment groups. A small number of procedural complications of balloon angioplasty were reported (haematoma at the site of catheter insertion (6.5%), femoral artery pseudoaneurysm (0.7%), renal artery or kidney perforation or dissection (2.5%) as well as peri-procedural deaths (0.4%)). No side effects of medical therapy were reported.

AUTHORS' CONCLUSIONS

The available data are insufficient to conclude that revascularisation in the form of balloon angioplasty, with or without stenting, is superior to medical therapy for the treatment of atherosclerotic renal artery stenosis in patients with hypertension. However, balloon angioplasty results in a small improvement in diastolic blood pressure and a small reduction in antihypertensive drug requirements. Balloon angioplasty appears safe and results in similar numbers of cardiovascular and renal adverse events to medical therapy.

Circulating and renal vein levels of microRNAs in patients with renal artery stenosis

BACKGROUND

MicroRNAs (miRs) are small non-coding RNAs that are important regulators of gene expression and have been implicated in atherosclerosis. Kidney injury distal to atherosclerotic renal artery stenosis (ARAS) is aggravated by atherosclerosis. Therefore, this study tested the hypothesis that renal miR expression would be altered in patients with ARAS.

METHODS

Patients with essential hypertension (EH; n = 13) or ARAS (n = 13) underwent a 3-day protocol study under controlled conditions. For miR levels, blood samples were collected from EH and ARAS renal vein (RV) and inferior vena cava or peripheral vein of matched normotensive healthy volunteers (HV; n = 13) and patients with coronary atherosclerosis (CA; n = 11). Single-renal blood flow was measured in EH and ARAS using computer tomography to calculate renal gradients and release of miRs.

RESULTS

Glomerular filtration rate (GFR) was lower in ARAS compared with the other groups. Systemic levels of most miRs were elevated in CA. RV miR levels were lower than systemic levels in both ARAS and EH. GFR-adjusted RV levels of miR-21, 155 and 210 were reduced only in ARAS patients compared with systemic levels in HV, although cross-kidney gradients were not different from EH. RV levels of miR-21, 126, 155 and 210 correlated with GFR.

CONCLUSIONS

Levels of atherosclerosis-related miR-21, 126, 155 and 210 are decreased in the stenotic-kidney vein of ARAS compared with EH patients, likely due to decreased GFR. Yet, these miRs might be implicated in modulating renal injury in ARAS, and their RV level may be a marker reflecting their renal expression.

New magnetic resonance imaging methods in nephrology

Established as a method to study anatomic changes, such as renal tumors or atherosclerotic vascular disease, magnetic resonance imaging (MRI) to interrogate renal function has only recently begun to come of age. In this review, we briefly introduce some of the most important MRI techniques for renal functional imaging, and then review current findings on their use for diagnosis and monitoring of major kidney diseases. Specific applications include renovascular disease, diabetic nephropathy, renal transplants, renal masses, acute kidney injury, and pediatric anomalies. With this review, we hope to encourage more collaboration between nephrologists and radiologists to accelerate the development and application of modern MRI tools in nephrology clinics.

Diagnosis and treatment of glomerular diseases in elderly patients

Glomerular diseases are common in elderly patients and are a major cause of kidney failure. Most glomerular diseases in the elderly are caused by chronic systemic diseases, including arterial hypertension, diabetes, and atherosclerotic vascular diseases, although acute systemic vasculitis, especially anti-neutrophil-cytoplamic-antibody-mediated vasculitis, and membranous nephropathy related to malignancy, drug toxicity, and idiopathic form also occur often. Complex age-related changes and sensitivity to drug toxicity can render diagnosis and treatment for elderly patients challenging. As the general population is aging and the rate of CKD rising, updating knowledge on managing these patients is critical for care providers. We provide a comprehensive review and update of the diagnosis and treatment of glomerular diseases in the elderly.

Cardiac function in renovascular hypertensive patients with and without renal dysfunction

BACKGROUND

Hypertension impairs left ventricular (LV) diastolic and systolic function, which might be aggravated by inflammation or neurohumoral activation. We hypothesized that LV diastolic dysfunction is more common in patients with renovascular hypertension (RVHT) compared with essential hypertension (EHT).

METHODS

Hypertensive patients who underwent both renal imaging to exclude RVHT and cardiac echocardiography within a 3-year period were identified retrospectively. Patients with significant renovascular disease were included in the RVHT group (n = 75); those without significant renovascular disease were included in the EHT group (n = 69). Cardiac function and structure were compared.

RESULTS

Baseline renal function was preserved (serum creatinine ≤ 2mg/dl) in EHT patients and impaired (serum creatinine > 2mg/dl) in only 9 RVHT patients. RVHT patients had higher systolic blood pressure, E/e' ratio, and greater prevalence of concentric hypertrophy but lower estimated glomerular-filtration-rate (eGFR) compared with EHT patients. Increased prevalence of LV diastolic dysfunction remained statistically significant in patients with RVHT after multivariable adjustment for age, sex, blood pressure, eGFR, diabetes, smoking, and statin use, with a relative risk (95% CI) for abnormal E/e' of 1.70 (95% confidence interval = 1.05-2.90; P = 0.03) compared with EHT. RVHT patients with severe renal dysfunction showed greater impairments in cardiac systolic and diastolic function compared with those in EHT patients or preserved renal function RVHT patients.

CONCLUSIONS

Among hypertensive patients undergoing echocardiography, cardiac structure and diastolic function are impaired in RVHT patients compared with EHT patients and remain different after adjustment for multiple significant covariables. When associated with significant renal dysfunction, RVHT aggravates LV hypertrophy and both systolic and diastolic dysfunction. Hence, identification of RVHT and renal dysfunction warrants development of targeted management strategies.

Darkness at the end of the tunnel: poststenotic kidney injury

Renal artery stenosis remains an important contributor to renal failure in the elderly population, but uncertainty continues to surround the mechanisms underlying progressive renal dysfunction. Here, we present the current understanding of the pathogenic mechanisms responsible for renal injury in these patients, with emphasis on those involved in disease progression.

Management of patients with resistant hypertension: current treatment options

Resistant hypertension (RHTN) is an increasingly common clinical problem that is often heterogeneous in etiology, risk factors, and comorbidities. It is defined as uncontrolled blood pressure on optimal doses of three antihypertensive agents, ideally one being a diuretic. The definition also includes controlled hypertension with use of four or more antihypertensive agents. Recent observational studies have advanced the characterization of patients with RHTN. Patients with RHTN have higher rates of cardiovascular events and mortality compared with patients with more easily controlled hypertension. Secondary causes of hypertension, including obstructive sleep apnea, primary aldosteronism, renovascular disease, are common in patients with RHTN and often coexist in the same patient. In addition, RHTN is often complicated by metabolic abnormalities. Patients with RHTN require a thorough evaluation to confirm the diagnosis and optimize treatment, which typically includes a combination of lifestyle adjustments, and pharmacologic and interventional treatment. Combination therapy including a diuretic, a long-acting calcium channel blocker, an angiotensin-converting enzyme inhibitor, a beta blocker, and a mineralocorticoid receptor antagonist where warranted is the classic regimen for patients with treatment-resistant hypertension. Mineralocorticoid receptor antagonists like spironolactone or eplerenone have been shown to be efficacious in patients with RHTN, heart failure, chronic kidney disease, and primary aldosteronism. Novel interventional therapies, including baroreflex activation and renal denervation, have shown that both of these methods may be used to lower blood pressure safely, thereby providing exciting and promising new options to treat RHTN.

The current status of angioplasty of atherosclerotic renal artery stenosis for the treatment of hypertension

Atherosclerotic renal artery stenosis, a fairly common disease of older persons, is a manifestation of generalized atherosclerosis, and is often associated with coronary artery disease. It is frequently associated with hypertension and impaired renal function, and is perceived by many physicians to be the cause of hypertension and renal failure. For this reason, they believe that hypertension can be cured by performing percutaneous renal artery angioplasty (PTRA) with stent placement. This practice has led to an increase in angioplasties, especially by interventional cardiologists, although the results from several randomized studies comparing interventional therapy with medical therapy have shown no significant difference between the two treatment modalities in blood pressure reduction or change in renal function. Similar results have been found by nonrandomized trials with selective PTRA. For this review, a Medline search of the English literature was conducted from 2006 to 2012, and 13 pertinent studies were selected. These studies with collateral literature will be discussed in this concise review.

Stent revascularization restores cortical blood flow and reverses tissue hypoxia in atherosclerotic renal artery stenosis but fails to reverse inflammatory pathways or glomerular filtration rate

BACKGROUND

Atherosclerotic renal artery stenosis (ARAS) is known to reduce renal blood flow, glomerular filtration rate (GFR) and amplify kidney hypoxia, but the relationships between these factors and tubulointerstitial injury in the poststenotic kidney are poorly understood. The purpose of this study was to examine the effect of renal revascularization in ARAS on renal tissue hypoxia and renal injury.

METHODS AND RESULTS

Inpatient studies were performed in patients with ARAS (n=17; >60% occlusion) before and 3 months after stent revascularization, or in patients with essential hypertension (n=32), during fixed Na(+) intake and angiotensin converting enzyme/angiotensin receptors blockers Rx. Single kidney cortical, medullary perfusion, and renal blood flow were measured using multidetector computed tomography, and GFR by iothalamate clearance. Tissue deoxyhemoglobin levels (R(2)*) were measured by blood oxygen level-dependent MRI at 3T, as was fractional kidney hypoxia (percentage of axial area with R(2)*>30/s). In addition, we measured renal vein levels of neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α. Pre-stent single kidney renal blood flow, perfusion, and GFR were reduced in the poststenotic kidney. Renal vein neutrophil gelatinase-associated lipocalin, tumor necrosis factor-α, monocyte chemoattractant protein-1, and fractional hypoxia were higher in untreated ARAS than in essential hypertension. After stent revascularization, fractional hypoxia fell (P<0.002) with increased cortical perfusion and blood flow, whereas GFR and neutrophil gelatinase-associated lipocalin, monocyte chemoattractant protein-1, and tumor necrosis factor-α remained unchanged.

CONCLUSIONS

These data demonstrate that despite reversal of renal hypoxia and partial restoration of renal blood flow after revascularization, inflammatory cytokines and injury biomarkers remained elevated and GFR failed to recover in ARAS. Restoration of vessel patency alone failed to reverse tubulointerstitial damage and partly explains the limited clinical benefit of renal stenting. These results identify potential therapeutic targets for recovery of kidney function in renovascular disease.

Human renovascular disease: estimating fractional tissue hypoxia to analyze blood oxygen level-dependent MR

PURPOSE

To test the hypothesis that fractional kidney hypoxia, measured by using blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging, correlates with renal blood flow (RBF), tissue perfusion, and glomerular filtration rate (GFR) in patients with atherosclerotic renal artery stenosis (RAS) better than regionally selected region of interest-based methods.

MATERIALS AND METHODS

The study was approved by the institutional review board according to a HIPAA-compliant protocol, with written informed consent. BOLD MR imaging was performed in 40 patients with atherosclerotic RAS (age range, 51-83 years; 22 men, 18 women) and 32 patients with essential hypertension (EH) (age range, 26-85 years; 19 men, 13 women) during sodium intake and renin-angiotensin blockade. Fractional kidney hypoxia (percentage of entire axial image section with R2* above 30 sec(-1)) and conventional regional estimates of cortical and medullary R2* levels were measured. Stenotic and nonstenotic contralateral kidneys were compared for volume, tissue perfusion, and blood flow measured with multidetector computed tomography. Statistical analysis was performed (paired and nonpaired t tests, linear regression analysis).

RESULTS

Stenotic RBF was reduced compared with RBF of contralateral kidneys (225.2 mL/min vs 348 mL/min, P = .0003). Medullary perfusion in atherosclerotic RAS patients was lower than in EH patients (1.07 mL/min per milliliter of tissue vs 1.3 mL/min per milliliter of tissue, P = .009). While observer-selected cortical R2* (18.9 sec(-1) [stenosis] vs 18.5 sec(-1) [EH], P = .07) did not differ, fractional kidney hypoxia was higher in stenotic kidneys compared with kidneys with EH (17.4% vs 9.6%, P < .0001) and contralateral kidneys (7.2%, P < .0001). Fractional hypoxia correlated inversely with blood flow (r = -0.34), perfusion (r = -0.3), and GFR (r = -0.32).

CONCLUSION

Fractional tissue hypoxia rather than cortical or medullary R2* values used to assess renal BOLD MR imaging demonstrated a direct relationship to chronically reduced blood flow and GFR.

Percutaneous renal artery angioplasty and stenting: indications, technique and results

BACKGROUND

Percutaneous interventions for renal arterial disease can be used to treat a variety of conditions including both atherosclerotic and non-atherosclerotic renal artery stenosis (RAS) as well as endovascular management of renal artery aneurysms (RAA).

AIM

We sought to examine the indications, techniques and results of percutaneous renal angioplasty and stenting in our institution over a 6-year period and review the current evidence for practice.

METHODS

Patient demographics, procedure indications, technical procedural details, complications, baseline and follow-up renal profile indices were analysed.

RESULTS

The most common indication for intervention was atherosclerotic RAS (69.2%) followed by RAS secondary to fibromuscular dysplasia (15.3%) and RAA (15.3%). There was a 100% technical success in our cohort of patients. The majority of patients (84.6%) had cross-sectional imaging in the form of computed tomography or magnetic resonance angiography prior to intervention.

CONCLUSION

When performed in appropriate settings following close liaison with referring physicians, percutaneous renal angioplasty and stenting remains an important treatment modality for renovascular disease.

Chronic renovascular hypertension is associated with elevated levels of neutrophil gelatinase-associated lipocalin

BACKGROUND

Renovascular hypertension (RVH) is characterized by chronic inflammation of the stenotic kidney and progressive renal dysfunction. Neutrophil gelatinase-associated lipocalin (NGAL), an acute phase protein induced in inflammatory conditions and ischemia, is a novel biomarker for acute kidney injury. We hypothesized that chronic RVH would be associated with increased renal and circulating NGAL levels.

METHODS

We prospectively measured renal vein and inferior vena cava (IVC) levels of NGAL and inflammatory cytokines in essential hypertensive (EH) and RVH patients, during constant sodium intake and anti-hypertensive regimens, and compared them with systemic levels in age-matched normotensive subjects (n = 22 each). In addition, we measured urinary NGAL and kidney injury molecule (KIM)-1 in all patients.

RESULTS

Blood pressure, serum creatinine, estimated glomerular filtration rate (eGFR), lipid panels and medications were similar in RVH and EH. Systemic, stenotic and contralateral renal vein levels of NGAL were all similarly elevated in RVH versus normal hypertension and EH (P < 0.05), as were renal vein levels of inflammatory markers like tumor necrosis factor-α. Furthermore, renal vein NGAL levels inversely correlated with eGFR, and directly with renal vein (but not systemic) levels of inflammatory markers. Urinary levels of NGAL and KIM-1 were elevated in both EH and RVH, as were systemic levels of C-reactive protein.

CONCLUSIONS

Chronic RVH is associated with elevated NGAL levels, likely due to ongoing kidney and systemic inflammation and ischemia. These findings may also imply the occurrence of the inflammation process in chronic RVH, which might contribute to the poorer outcomes of RVH compared with EH patients.

Inflammatory and injury signals released from the post-stenotic human kidney

AIMS

The mechanisms mediating kidney injury and repair in humans with atherosclerotic renal artery stenosis (ARAS) remain poorly understood. We hypothesized that the stenotic kidney releases inflammatory mediators and recruits progenitor cells to promote regeneration.

METHODS AND RESULTS

Essential hypertensive (EH) and ARAS patients (n=24 each) were studied during controlled sodium intake and antihypertensive treatment. Inferior vena cava (IVC) and renal vein (RV) levels of CD34+/KDR+ progenitor cells, cell adhesion molecules, inflammatory biomarkers, progenitor cell homing signals, and pro-angiogenic factors were measured in EH and ARAS, and their gradient and net release compared with systemic levels in matched normotensive controls (n= 24). Blood pressure in ARAS was similar to EH, but the glomerular filtration rate was lower. Renal vein levels of soluble E-Selectin, vascular cell adhesion molecule-1, and several inflammatory markers were higher in the stenotic kidney RV vs. normal and EH RV (P < 0.05), and their net release increased. Similarly, stem-cell homing factor levels increased in the stenotic kidney RV. Systemic CD34+/KDR+ progenitor cell levels were lower in both EH and ARAS and correlated with cytokine levels. Moreover, CD34+/KDR+ progenitor cells developed a negative gradient across the ARAS kidney, suggesting progenitor cell retention. The non-stenotic kidney also showed signs of inflammatory processes, which were more subtle than in the stenotic kidney.

CONCLUSION

Renal vein blood from post-stenotic human kidneys has multiple markers reflecting active inflammation that portends kidney injury and reduced function. CD34+/KDR+ progenitor cells sequestered within these kidneys may participate in reparative processes. These inflammation-related pathways and limited circulating progenitor cells may serve as novel therapeutic targets to repair the stenotic kidney.

Blood oxygen level-dependent magnetic resonance imaging identifies cortical hypoxia in severe renovascular disease

Atherosclerotic renal artery stenosis has a range of manifestations depending on the severity of vascular occlusion. The aim of this study was to examine whether exceeding the limits of adaptation to reduced blood flow ultimately leads to tissue hypoxia, as determined by blood oxygen level dependent MRI. We compared 3 groups of hypertensive patients, 24 with essential hypertension, 13 with "moderate" (Doppler velocities 200-384 cm/s), and 17 with "severe" atherosclerotic renal artery stenosis (ARAS; velocities >384 cm/s and loss of functional renal tissue). Cortical and medullary blood flows and volumes were determined by multidetector computed tomography. Poststenotic kidney size and blood flow were reduced with ARAS, and tissue perfusion fell in the most severe lesions. Tissue medullary deoxyhemoglobin, as reflected by R2* values, was higher as compared with the cortex for all of the groups and did not differ between subjects with renal artery lesions and essential hypertension. By contrast, cortical R2* levels were elevated for severe ARAS (21.6±9.4 per second) as compared with either essential hypertension (17.8±2.3 per second; P<0.01) or moderate ARAS (15.7±2.1 per second; P<0.01). Changes in medullary R2* after furosemide administration tended to be blunted in severe ARAS as compared with unaffected (contralateral) kidneys. These results demonstrate that severe vascular occlusion overwhelms the capacity of the kidney to adapt to reduced blood flow, manifest as overt cortical hypoxia as measured by blood oxygen level-dependent MRI. The level of cortical hypoxia is out of proportion to the medulla and may provide a marker to identify irreversible parenchymal injury.

Current opinions in renovascular hypertension

Renal artery stenosis and renovascular hypertension are important considerations in patients with hypertension that is difficult to control. The diagnosis may also have prognostic significance for progressive renal disease. The most common causes of renal artery stenosis are atherosclerotic disease and fibromuscular dysplasia. The pathophysiology of renal artery stenosis is reviewed, and the pros and cons of various imaging studies in the appropriate clinical setting are discussed. Treatment includes aggressive control of hypertension, dealing with associated cardiac risk factors, and angioplasty or surgery in specific circumstances.

Role of the kidneys in resistant hypertension

Resistant hypertension is a failure to achieve goal BP (<140/90 mm Hg for the overall population and <130/80 mm Hg for those with diabetes mellitus or chronic kidney disease) in a patient who adheres to maximum tolerated doses of 3 antihypertensive drugs including a diuretic. The kidneys play a critical role in long-term regulation of blood pressure. Blunted pressure natriuresis, with resultant increase in extracellular fluid volume, is an important cause of resistant hypertension. Activation of the renin-angiotensin-aldosterone system, increased renal sympathetic nervous system activity and increased sodium reabsorption are important renal mechanisms. Successful treatment requires identification and reversal of lifestyle factors or drugs contributing to treatment resistance, diagnosis and appropriate treatment of secondary causes of hypertension, use of effective multidrug regimens and optimization of diuretic therapy. Since inappropriate renal salt retention underlies most cases of drug-resistant hypertension, the therapeutic focus should be on improving salt depleting therapy by assessing and, if necessary, reducing dietary salt intake, optimizing diuretic therapy, and adding a mineralocorticoid antagonist if there are no contraindications.

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.

Management of high blood pressure in Blacks: an update of the International Society on Hypertension in Blacks consensus statement

Since the first International Society on Hypertension in Blacks consensus statement on the "Management of High Blood Pressure in African American" in 2003, data from additional clinical trials have become available. We reviewed hypertension and cardiovascular disease prevention and treatment guidelines, pharmacological hypertension clinical end point trials, and blood pressure-lowering trials in blacks. Selected trials without significant black representation were considered. In this update, blacks with hypertension are divided into 2 risk strata, primary prevention, where elevated blood pressure without target organ damage, preclinical cardiovascular disease, or overt cardiovascular disease for whom blood pressure consistently <135/85 mm Hg is recommended, and secondary prevention, where elevated blood pressure with target organ damage, preclinical cardiovascular disease, and/or a history of cardiovascular disease, for whom blood pressure consistently <130/80 mm Hg is recommended. If blood pressure is ≤10 mm Hg above target levels, monotherapy with a diuretic or calcium channel blocker is preferred. When blood pressure is >15/10 mm Hg above target, 2-drug therapy is recommended, with either a calcium channel blocker plus a renin-angiotensin system blocker or, alternatively, in edematous and/or volume-overload states, with a thiazide diuretic plus a renin-angiotensin system blocker. Effective multidrug therapeutic combinations through 4 drugs are described. Comprehensive lifestyle modifications should be initiated in blacks when blood pressure is ≥115/75 mm Hg. The updated International Society on Hypertension in Blacks consensus statement on hypertension management in blacks lowers the minimum target blood pressure level for the lowest-risk blacks, emphasizes effective multidrug regimens, and de-emphasizes monotherapy.

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.

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

Improved technology for detection of and endovascular procedures for renal artery stenosis due to atherosclerosis has been associated with increases in renal artery intervention. Hypertension with accelerated target organ injury, reduced kidney function, and episodic circulatory congestion in patients with renovascular disease predict reduced patient survival. Recent studies indicate that activation of pressor mechanisms depends upon hemodynamic gradients that are often overrated by visual estimates. Although activation of the renin-angiotensin system initiates renovascular hypertension, additional mechanisms perpetuate vascular remodeling and kidney injury that may not depend upon large vessel occlusion. Major advances in medical therapy have led to initiation of at least 4 major prospective trials comparing optimal medical therapy with or without stenting. Up to now, outcome data fail to support broad application of renal revascularization, including results from a recent large, prospective trial from the United Kingdom, despite small groups of patients that experience major clinical benefit. The ambiguity of these results partly reflect poor characterization of the severity of vascular lesions and competing risks within the population related to aging and pre-existing disease. Many patients currently undergoing renal artery interventions derive little net benefit and some are exposed to significant complications, including atheroembolic disease. Determining the appropriate role for renal artery interventions will depend on developing better methods for judging the role of large vessel occlusive disease regarding tissue oxygenation, activation of profibrotic pathways, and irreversible injury in the post-stenotic kidney.

Revascularization versus medical therapy for renal-artery stenosis. The ASTRAL Investigators. The New England Journal of Medicine 2009; 361: 1953—1962

Study objective: The objective of ASTRAL was to determine whether percutaneous revascularization combined with medical therapy compared to medical therapy alone improves renal function and other outcomes, such as blood pressure, time to first renal event, time to first major cardiovascular event, and mortality.

Study population: ASTRAL enrolled 806 patients with atherosclerotic renovascular disease from 57 centers. Patients were screened if treating clinicians felt they had clinical features suggestive of underlying atherosclerotic renovascular disease (i.e. hypertension refractory to medical therapy, or renal impairment as suggested by laboratory measurements). All patients had to have an imaging modality (i.e. computed tomographic angiography (CTA), magnetic resonance angiography (MRA) or renal artery ultrasound). This imaging had to convey that the patient had ‘substantial’ anatomical atherosclerotic stenosis in at least one renal artery that was suitable for endovascular therapy. Also, the treating clinician had to be ‘uncertain’ that the patient would benefit from revascularization. Fifty-nine percent of patients were reported to have renal artery stenosis of > 70%, and 60% had a serum creatinine of ≥ 150 mmol per liter.

Design and methods: ASTRAL was a randomized, unblinded study of patients with atherosclerotic renal artery disease who were assigned to percutaneous revascularization plus best medical therapy or best medical therapy alone. The primary outcome of the ASTRAL trial was the change of renal function over time, as determined by the mean slope of the reciprocal of serum creatinine. Secondary outcomes included blood pressure, time to first renal event (defined as: new onset of kidney injury, dialysis, renal transplantation, nephrectomy, or death from renal failure), time to first major cardiovascular event (defined as: myocardial infarction, stroke, death from cardiovascular cause, hospitalization for angina, fluid overload or congestive heart failure, coronary artery revascularization, or another peripheral arterial procedure), and all-cause mortality. Randomization was 1:1 via computer algorithm and was stratified by serum creatinine, glomerular filtration rate (GFR), severity of renal artery stenosis, kidney length on ultrasound, and rate of progression of renal impairment. Patients who were assigned to the revascularization plus medical therapy arm underwent percutaneous revascularization within 4 weeks. The procedure type (angioplasty alone or with stenting), was left to the discretion of the local operator. Distal protection devices were not used. Medical therapy in both arms consisted of antihypertensive drugs, statins, and antiplatelet agents. The trial was powered to detect a 20% reduction in the mean slope of the reciprocal of serum creatinine. Based on low crossover rates, it was determined that at least 750 patients would have to be enrolled. Analysis was by intention to treat. Continuous variables were subject to repeated measures analysis. Time-to-event data were expressed via Kaplan Meier curves and compared via log-rank testing. Prespecified subgroup analyses included baseline serum creatinine, GFR, severity of renal artery stenosis, kidney length, and progression of renal disease.

Results: Of the 806 patients included, 403 were randomized to the revascularization arm and 403 to medical therapy only. The median follow-up was 34 months. Only 337 (83%) patients randomized to revascularization underwent the procedure, whereas 24 patients (6%) randomized to the medical therapy arm underwent revascularization. The number of antihypertensive medications used was greater in the medical therapy group than in the revascularization group at the 12-month follow-up: 2.97 versus 2.77 ( p = 0.03). The mean slope of the reciprocal of the serum creatinine concentration was —0.07 × 10— 3 liters per micromole per year in the revascularization group versus —0.13 × 10—3 liters per micromole per year in the medical-therapy group (difference of 0.06 × 10 —3 liters per micromole per year) (95% confidence interval [CI], —0.002 to 0.13, p = 0.06) with a trend favoring revascularization. After 5 years of follow-up, there was a trend toward lower mean systolic blood pressure (1.6 mmHg lower, p = 0.06) in the revascularization group. However, the mean diastolic blood pressure was significantly lower in the medical therapy group at long-term follow-up (divergence of slope of mean diastolic blood pressure: 0.61 mmHg per year, p = 0.03). There was no significant difference between renal events, time to first renal event, acute kidney injury, or development of end-stage renal disease in either group. Further, there was no difference in major cardiovascular events or overall survival in either group. The periprocedural complication rate within the revascularization group was 9% (31/359 patients). Fifty-five out of 280 patients (20%) had an adverse event by 1 month post procedure. Overall, there were 31 serious complications of revascularization in 23 patients. Per protocol analysis of patients suggested that there was no significant difference in outcomes between patients who received revascularization versus medical therapy. No differences between treatment groups were identified in any of the pre-specified subgroup analyses.

Conclusions: Renal artery stenting combined with medical therapy did not improve renal function compared to medical therapy alone in patients with atherosclerotic renal artery disease.

Preserved oxygenation despite reduced blood flow in poststenotic kidneys in human atherosclerotic renal artery stenosis

Atherosclerotic renal artery stenosis reduces blood flow and perfusion pressures to the poststenotic kidney producing renovascular hypertension and threatening glomerular filtration rate. Little is known regarding regional tissue oxygenation in human renovascular disease that develops slowly. We compared stenotic and contralateral kidneys regarding volume, tissue perfusion, blood flow measured by multidetector computed tomography, and blood oxygen level-dependent magnetic resonance values in the cortex and medulla in 14 patients with unilateral stenosis (mean: 71% by quantitative computed tomography) and in 14 essential hypertensive patients during 150 mEq/d of sodium intake and renin-angiotensin blockade. Stenotic kidney volume was reduced compared with the contralateral kidney (118.6+/-9.9 versus 155.4+/-13.7 mL; P<0.01), as was total blood flow (269.7+/-42.2 versus 383.7+/-49; P=0.02), mainly because of reduced cortical volume. Tissue perfusion was similar but lower than essential hypertension (1.5 versus 1.2 mL/min per milliliter; P<0.05). Blood oxygen level-dependent MR at 3 T confirmed elevated R2* values (a measure of deoxyhemoglobin) in deep medullary regions in all 3 sets of kidneys (38.9+/-0.7 versus cortex 17.8+/-0.36 s(-1); P<0.0001). Despite reduced blood flow, R2* values did not differ between atherosclerotic and essential hypertensive kidneys, although furosemide-suppressible fall in medullary R2* was reduced in stenotic kidneys (5.7+/-1.8 versus 9.4+/-1.9 s(-1); P<0.05). Renal venous oxygen levels from the stenotic kidney were higher than those from essential hypertensives (65.1+/-2.2 versus 58.1+/-1.2; P=0.006). These data indicate that, although stenosis reduced blood flow and volume, cortical and medullary oxygenation was preserved under these conditions.

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.

Limitations of angiography for the assessment of renal artery stenosis and treatment implications

Renovascular hypertension due to atherosclerotic renal artery stenosis is the most common cause of secondary hypertension. Percutaneous catheter-based renal artery revascularization has been increasingly utilized for the treatment of renal artery stenosis. Renal artery stenting has a high technical success rate, but the rate of improvement in hypertension is somewhat less than expected with this technique. Misinterpretation of angiographic images may play a role in these unfavorable clinical results. We present a case in which the diagnosis of severe renal artery stenosis was not apparent by angiography. Intravascular ultrasound and translesional pressure gradient measurements during arteriography can help to determine the precise severity of stenosis and may augment the clinical results of percutaneous renal artery stent placement.

Advances in contrast-enhanced MR angiography of the renal arteries

Renal artery stenosis (RAS) is a potentially curable cause of renovascular hypertension (RVH) and is caused by either atherosclerosis or fibromuscular dysplasia in the vast majority of patients. Although intra-arterial digital subtraction angiography is still considered the standard of reference test for the anatomic diagnosis of RAS, MR angiography and functional renal MR imaging are promising alternatives that also allow for functional characterization of RAS. This article provides an overview of these techniques and discusses their relative merits and shortcomings. Because missing RVH may have serious consequences the most important requirement for an alternative test is that it has high sensitivity. An unresolved issue is the prediction of functional recovery after therapy.