Revascularization of renal artery stenosis in patients with renal insufficiency

When and How Should We Revascularize Patients With Atherosclerotic Renal Artery Stenosis?

Atherosclerotic renal artery stenosis is the leading cause of secondary hypertension and may lead to resistant (refractory) hypertension, progressive decline in renal function, and cardiac destabilization syndromes (pulmonary edema, recurrent heart failure, or acute coronary syndromes) despite guideline-directed medical therapy. Although randomized controlled trials comparing medical therapy with medical therapy and renal artery stenting have failed to show a benefit for renal artery stenting, according to comparative effectiveness reviews by the Agency for Healthcare Research and Quality, the trials may not have enrolled patients with the most severe atherosclerotic renal artery stenosis, who would be more likely to benefit from renal stenting. Because of limitations of conventional angiography, it is critical that the hemodynamic severity of moderately severe (50% to 70%) atherosclerotic renal artery stenosis lesions be confirmed on hemodynamic measurement. The authors review techniques to optimize patient selection, to minimize procedural complications, and to facilitate durable patency of renal stenting. The authors also review the current American College of Cardiology and American Heart Association guidelines and the Society for Cardiovascular Angiography and Interventions appropriate use criteria as they relate to renal stenting.

Intravascular Delivery of Biologics to the Rat Kidney

The renal microvascular compartment plays an important role in the progression of kidney disease and hypertension, leading to the development of End Stage Renal Disease with high risk of death for cardiovascular events. Moreover, recent clinical studies have shown that renovascular structure and function may have a great impact on functional renal recovery after surgery. Here, we describe a protocol for the delivery of drugs into the renal artery of rats. This procedure offers significant advantages over the frequently used systemic administration as it may allow a more localized therapeutic effect. In addition, the use of rodents in pharmacodynamic analysis of preclinical studies may be cost effective, paving the way for the design of translational experiments in larger animal models. Using this technique, infusion of rat recombinant Vascular Endothelial Growth Factor (VEGF) protein in rats has induced activation of VEGF signaling as shown by increased expression of FLK1, pAKT/AKT, pERK/ERK. In summary, we established a protocol for the intrarenal delivery of drugs in rats, which is simple and highly reproducible.

Effects of Stenting for Atherosclerotic Renal Artery Stenosis on eGFR and Predictors of Clinical Events in the CORAL Trial

BACKGROUND AND OBJECTIVES

Atherosclerotic renal artery stenosis may cause kidney function loss, but effects of stenting on eGFR and clinical events associated with CKD are uncertain. Our study objectives were to determine effects of stenting on eGFR and predictors of clinical events.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Participants (n=931) in the Cardiovascular Outcomes in Renal Artery Stenosis Trial (from May of 2005 to September of 2012) had >60% atherosclerotic renal artery stenosis and systolic hypertension on two or more antihypertensive drugs and/or stage ≥3 CKD. The intervention was stenting versus no stenting on a background of risk factor management: renin-angiotensin system inhibition, statin, antiplatelet therapy, and smoking cessation education. The effect of stenting on eGFR by the serum creatinine-cystatin C Chronic Kidney Disease Epidemiology Collaboration equation was the prespecified analysis of kidney function. Predictors of eGFR and CKD outcomes (≥30% eGFR loss, ESRD, and death) and cardiovascular disease outcomes (stroke, myocardial infarction, heart failure, and death) controlling for eGFR and albuminuria were also determined.

RESULTS

eGFR was 59±24 ml/min per 1.73 m(2) (mean±SD) at baseline. Over 3 years, eGFR change, assessed by generalized estimating equations, was -1.5±7.0 ml/min per 1.73 m(2) per year in the stent group versus -2.3±6.3 ml/min per 1.73 m(2) per year in the medical therapy only group (P=0.18). eGFR predictors (multiple variable generalized estimating equations) were age, albuminuria, systolic BP, and diabetes (inverse associations) as well as men, total cholesterol, and HDL cholesterol (positive associations). CKD outcomes events occurred in 19% (175 of 931), and predictors (Cox proportional hazards models) included albuminuria (positive association), systolic BP (positive association), and HDL cholesterol (inverse association). Cardiovascular disease outcomes events occurred in 22% (207 of 931), and predictors included age, albuminuria, total cholesterol, prior cardiovascular disease, and bilateral atherosclerotic renal artery stenosis (positive associations).

CONCLUSIONS

Stenting did not influence eGFR in participants with atherosclerotic renal artery stenosis receiving renin-angiotensin system inhibition-based therapy. Predictors of clinical events were traditional risk factors for CKD and cardiovascular disease.

Early atherosclerosis aggravates renal microvascular loss and fibrosis in swine renal artery stenosis

Renal function in patients with atherosclerosis and renal artery stenosis (ARAS) deteriorates more frequently than in nonatherosclerotic RAS. We hypothesized that ARAS aggravates stenotic-kidney micro vascular loss compared to RAS. Domestic pigs were randomized to normal, RAS, and ARAS (RAS fed a high-cholesterol diet) groups (n = 7 each). Ten weeks later stenotic-kidney oxygenation, renal blood flow, and glomerular filtration rate (GFR) were evaluated in vivo, and micro vascular density by micro-computed tomography. Blood pressure in both RAS and ARAS was elevated; and stenotic-kidney renal blood flow and GFR similarly decreased. RAS decreased the density of small-size cortical microvessels (<200 μm), whereas ARAS extended the decrease to medium-sized microvessels (200-300 μm). Cortical hypoxia and interstitial fibrosis increased in both RAS and ARAS but correlated inversely with micro vascular density only in RAS. Atherosclerosis aggravates loss of stenotic-kidney microvessels, yet additional determinants likely contribute to cortical hypoxia and fibrosis in swine ARAS.

Revascularization as a treatment to improve renal function

An aging atherosclerosis-prone population has led to an increase in the prevalence of atherosclerotic renovascular disease (ARVD). Medical management of this disease, as with other atherosclerotic conditions, has improved over the past decade. Despite the widespread availability of endovascular revascularization procedures, there is inconsistent evidence of benefit in ARVD and no clear consensus of opinion as to the best way to select suitable patients for revascularization. Several published randomized controlled trials have attempted to provide clearer evidence for best practice in ARVD, but they have done so with varying clarity and success. In this review, we provide an overview of ARVD and its effect on renal function. We present the currently available evidence for best practice in the management of patients with ARVD with a particular focus on revascularization as a treatment to improve renal function. We provide a brief overview of the evidence for revascularization in other causes of renal artery stenosis.

The prevalence and meaning of eosinophilia in renal diseases on a nephrology consultation service

BACKGROUND

In recent years, we have come to understand that the eosinophil is more than the end point in clearance of parasitic infection or a maladaptive response to asthma and allergic reactions. Since eosinophilia has been reported to be common in renal diseases, we thought that an evaluation of the associations of eosinophilia on a renal consultation service would add some value to the understanding of their role in renal disease.

METHODS

This was a prospective cross-sectional study of 1339 consecutive patients referred to the nephrology service after hospitalization who were evaluated for the relationship of the amount of serum eosinophils to their diagnosis, gender, age and the presence of autoimmune disease, cancer, infection, liver disease, pleural effusions, allergies and use of prednisone, beta-blockers or beta agonists, in addition to the total white blood count, urine protein, serum concentration creatinine and phosphorus levels and estimated glomerular filtration rate.

RESULTS

The presence of vascular disease correlated the most strongly with increased eosinophil count (partial correlation coefficient, r = 0.18, P = 0.006), followed by pleural effusions (r = 0.17, P = 0.001), while total white cell count (r = -0.18, P = 0.008) and administration of beta-blockers (r = -0.13, P = 0.047) demonstrated significant inverse correlations and the presence of autoimmune disease, cancer, allergies, proteinuria and serum phosphorus concentration demonstrated no significant correlation.

CONCLUSION

There are multiple associations with increased eosinophil counts in patients seen on a nephrology consultant service; however, their presence appears less often in association with allergies or uremia and more often with vascular disease.

Mechanisms of tissue injury in renal artery stenosis: ischemia and beyond

Renal injury distal to an atherosclerotic renovascular obstruction reflects multiple intrinsic factors producing parenchymal tissue injury. Atherosclerotic disease pathways superimposed on renal arterial obstruction may aggravate damage to the kidney and other target organs, and some of the factors activated by renal artery stenosis may in turn accelerate the progression of atherosclerosis. This cross-talk is mediated through amplified activation of renin-angiotensin system, oxidative stress, inflammation, and fibrosis-pathways notoriously involved in renal disease progression. Oxidation of lipids also accelerates the development of fibrosis in the stenotic kidney by amplifying profibrotic mechanisms and disrupting tissue remodeling. The extent to which actual ischemia modulates injury in the stenotic kidney has been controversial, partly because the decrease in renal oxygen consumption usually parallels a decrease in renal blood flow, and because renal vein oxygen pressure in the affected kidney is not decreased. However, recent data using novel methodologies demonstrate that intra-renal oxygenation is heterogeneously affected in different regions of the kidney. Activation of such local injury within the kidney may lead to renal dysfunction and structural injury, and ultimately unfavorable and irreversible renal outcomes. Identification of specific pathways producing progressive renal injury may enable development of targeted interventions to block these pathways and preserve the stenotic kidney.

Positron-Emission Tomography Imaging of the Angiotensin II Subtype 1 Receptor in Swine Renal Artery Stenosis

The angiotensin II subtype 1 receptor (AT 1 R) has been linked to the development and progression of renovascular hypertension. In this study we applied a pig model of renovascular hypertension to investigate the AT 1 R in vivo with positron-emission tomography (PET) and in vitro with quantitative autoradiography. AT 1 R PET measurements were performed with the radioligand [ 11 C]KR31173 in 11 control pigs and in 13 pigs with hemodynamically significant renal artery stenosis; 4 were treated with lisinopril for 2 weeks before PET imaging. The radioligand impulse response function was calculated by deconvolution analysis of the renal time-activity curves. Radioligand binding was quantified by the 80-minute retention of the impulse response function. Median values and interquartile ranges were used to illustrate group statistics. Radioligand retention was significantly increased ( P =0.044) in hypoperfused kidneys of untreated (0.225; range: 0.150 to 0.373) and lisinopril-treated (0.237; range:0.224 to 0.272) animals compared with controls (0.142; range:0.096 to 0.156). Increased binding of [ 11 C]KR31173 documented by PET in vivo was confirmed by in vitro autoradiography. Both in vivo and in vitro binding measurements showed that the effect of renal artery stenosis on the AT 1 R was not abolished by lisinopril treatment. These studies provide insight into kidney biology as the first in vivo/in vitro experimental evidence about AT 1 R regulation in response to reduced perfusion of the kidney. The findings support the concept of introducing AT 1 R PET as a diagnostic biomarker of renovascular disease.

[Atherosclerosis and the kidney]

Diffuse atherosclerosis entails a 15-30% risk of plaques on renal arteries (ARAS), with a correlation with coronary atherosclerosis. Ischemia induces generation of angiotensin II (Ang II) that maintains sufficient hydrostatic pressure within the tuft to preserve the GFR. Ang II inhibition suppresses this protective mechanism. In fact, any antihypertensive drug may lead to reaching a "critical perfusion pressure". ARAS should be suspected in case of renal asymmetry. It should also be envisaged in case of "flash pulmonary edemas". Ultrasonography and renal tomography show aortic calcifications and often the outline of an abdominal aortic aneurysm. Tomodensitometry may detect large aorto-renal plaques. Spiral scanner tomography represents a progress, in terms of renal artery imaging and of renal cortical atrophy. Magnetic resonance imaging is less accurate but avoids iodine toxicity. The best noninvasive method is pulsed echo-doppler. It is particularly useful for evaluating stenoses progression. Some stenoses progress to renal atrophy and renal artery thrombosis, whereas others follow a stable course. Pulsed Doppler helps predict whether revascularization will improve renal function, according to the resistance index. Renal arteriography entails a high risk of cholesterol crystal embolism. However, it is the obligatory first step for angioplasty and stent positioning, indicated when the kidney is not atrophic. The indication for revascularization essentially depends on evaluation of the benefits vs risks of angioplasty or surgery. Some publications underscore the frequent stability of renal function and the fact that, revascularized or not, most patients will shortly die of myocardial infarction. Renal cholesterol crystal embolism (CCE) is a severe condition, which occurs when large arteries undergo surgery, aortography or interventional radiology. Anticoagulants are a frequent cause of CCE. CCE may also occur spontaneously, resulting in slowly progressive renal insufficiency. Migration of crystals in small caliber intrarenal arteries induces obstruction, followed by an inflammatory reaction. The clinical picture resembles angiitis, with laboratory evidence of inflammation along with high eosinophil counts and hypocomplementemia. Diagnosis rests on: 1) a iatrogenic event in a patient with an atherosclerotic background; 2) examination of the skin disclosing purple toes, small necrotic lesions and livedo of the lower limbs. Crystals may also be found by funduscopy. Skin or muscle biopsy are contributive in showing crystals and help avoid renal biopsy; 3) other localizations involve the mesenteric circulation and the central nervous system. Until recently, the prognosis was considered disastrous. However, a recently published treatment schedule proved efficient in reducing mortality. A last issue regarding the relationships between atherosclerosis and the kidney deserves mention. In an autopsy-based study it was shown that atherosclerosis per se is accompanied by an increase in the glomerular surface area along with a greater proportion of obsolescent glomeruli by comparison with matched controls. Finally, it should be recalled that atherogenic hyperlipidemia usually aggravates the course of any renal disease, including ARAS. Treatment with statins is indicated in all forms of atherosclerotic renal disease.

Atheroemboli during renal artery angioplasty: An ex vivo study

OBJECTIVE

We hypothesized that atheroemboli released during renal angioplasty could be responsible for the modest functional result of renal angioplasty even after anatomic reduction of renal artery stenosis. To test this hypothesis, we enumerated and sized fragments released during ex vivo angioplasty and stenting of human renal artery atherosclerotic specimens removed during aortorenal endarterectomy.

METHODS

Thirty-three intact aortorenal atheroma specimens (16 pairs with adjacent aortic atheroma and one specimen with a single renal artery orifice) were removed from 17 patients with renal artery occlusive disease who underwent renal artery endarterectomy. specimens. Endarterectomy specimens were removed with a ring of aortic plaque and "fitted" with a polytetrafluoroethylene "adventitia". Ex vivo angioplasty was technically successful in 31 of the 33 specimens and was performed by using a 0.018-inch guidewire and 3.0-mm and 5.0-mm angioplasty balloons inflated for 30 seconds at 15 atmospheres pressure. Stenting was performed with either a 5-mm or 6-mm self-expanding Wallstent. Each artery was flushed with 20 mL of saline after guidewire placement, each angioplasty, and stent placement. The effluent was collected for analysis for counting with either a microscope (size >100 microm) or a Coulter counter (size <100 microm). The number and size of embolic fragments in the effluent collected after each manipulation was recorded.

RESULTS

Each manipulation of the specimens, including simply advancing the guidewire through the atherosclerotic lesion, released thousands of fragments. The numbers of fragments in each size category increased with decreasing particle size. Positioning and deploying the Wallstent released an additional bolus of fragments similar to that released after balloon angioplasty.

CONCLUSIONS

Ex vivo renal angioplasty releases thousands of atherosclerotic fragments of sufficient size to create vascular occlusions and initiate significant renal parenchymal damage. The results of renal angioplasty procedures could be improved by placing distal protection devices to prevent atheroembolization.

CLINICAL RELEVANCE

Athero-emboli produce a local arteritis in the kidney and could cause substantial damage to the renal parenchyma. This report explores the quantity of athero-emboli released during ex vivo angioplasty and stenting of renal atheroma specimens. The number of emboli found in this ex vivo study suggest that the use of protection devices may be advisable to protect the end organ, as done with angioplasty of the carotid artery. Of necessity, this was an ex vivo study and direct application to the clinical setting will need further study. Fortunately, multi-center trials examining the value of protection devices are currently in progress.

[Effect of renal revascularization techniques on renal function and blood pressure control]

BACKGROUND AND OBJECTIVE

Our objective was to assess the effect of renal revascularization on renal function and blood pressure control.

PATIENTS AND METHOD

Retrospective analysis of primary renal revascularization procedures performed during a 6-year period. Parameters of renal function and blood pressure control were assessed before and after the procedure.

RESULTS

Forty consecutive renal artery revascularizations were performed in 36 patients (12 aorto-renal bypasses and 28 percutaneous transluminal angioplasties, 4 bilateral). At the first month, the renal function improved in 50% cases, but at the mean follow-up it improved only in 26%. At the first month, blood pressure control improved in 50% patients, but at the mean follow-up, it only improved in 28%.

CONCLUSIONS

Renal revascularization does not offer a medium-term benefit in most patients.

Distinct renal injury in early atherosclerosis and renovascular disease

BACKGROUND

Atherosclerotic renovascular disease may augment deterioration of renal function and ischemic nephropathy compared with other causes of renal artery stenosis (RAS), but the underlying mechanisms remain unclear. This study was designed to test the hypothesis that concurrent early atherosclerosis and hypoperfusion might have greater early deleterious effects on the function and structure of the stenotic kidney.

METHODS AND RESULTS

Regional renal hemodynamics and function at baseline and during vasoactive challenge (acetylcholine or sodium nitroprusside) were quantified in vivo in pigs by electron-beam computed tomography after a 12-week normal (n=7) or hypercholesterolemic (HC, n=7) diet, RAS (n=6), or concurrent HC and a similar degree of RAS (HC+RAS, n=7). Flash-frozen renal tissue was studied ex vivo. Basal cortical perfusion and single-kidney glomerular filtration rate (GFR) were decreased similarly in the stenotic RAS and HC+RAS kidneys, but tubular fluid reabsorption was markedly impaired only in HC+RAS. Perfusion responses to challenge were similarly blunted in the experimental groups. Stimulated GFR increased in normal, HC, and RAS (38.3+/-3.6%, 36.4+/-7.6%, and 60.4+/-9.3%, respectively, P<0.05), but not in HC+RAS (6.5+/-15.1%). These functional abnormalities in HC+RAS were accompanied by augmented perivascular, tubulointerstitial, and glomerular fibrosclerosis, inflammation, systemic and tissue oxidative stress, and tubular expression of nuclear factor-kappaB and inducible nitric oxide synthase.

CONCLUSIONS

Early chronic HC+RAS imposes distinct detrimental effects on renal function and structure in vivo and in vitro, evident primarily in the tubular and glomerular compartments. Increased oxidative stress may be involved in the proinflammatory and progrowth changes observed in the stenotic HC+RAS kidney, which might potentially facilitate the clinically observed progression to end-stage renal disease.

Techniques for predicting a favourable response to renal angioplasty in patients with renovascular disease

Renovascular disease is present in some 10-40% of patients with end-stage renal disease, and constitutes the fastest-growing group of end-stage renal disease patients. The unselective correction of renal artery stenosis has led to disappointing results. Most studies that compared conservative treatment with angioplasty found only modest or no beneficial effects of angioplasty on renal function and blood pressure. It is therefore mandatory to evaluate the functional significance of a stenosis before intervention. Patients with a high likelihood of a favourable response should be identified. Factors that affect outcome include the severity of renal artery stenosis, the procedure used to treat renal artery stenosis (antihypertensive drugs, angioplasty with or without stenting, or surgery), radiocontrast nephrotoxicity, atheroembolism and, most importantly, underlying renal disease, forestalling a favourable response of renal function or blood pressure even after the successful correction of renal artery stenosis. Evaluation of the renal resistance index using Doppler ultrasound or captopril scintigraphy are the best methods by which to classify patients as responders or non-responders to intervention. Each factor has to be considered before the correction of renal artery stenosis to achieve satisfactory results with regard to an improvement in renal function and blood pressure.

Ischemic nephropathy

Ischemic nephropathy is a major cause of chronic renal failure in people over 50 years of age. In addition, renal artery stenosis is associated with increased mortality, particularly if renal or cardiac function is compromised. The diagnosis is made both by clinical characteristics and imaging studies. At present, duplex Doppler ultrasound and magnetic resonance angiography appear to be the most promising non-invasive screening tests. Although data from controlled trials are lacking, revascularization is the mainstay of therapy for ischemic nephropathy. Advances in percutaneous interventions now allow revascularization to be offered to many patients, including those who are poor surgical candidates. The role of medical therapies (statins, angiotensin-converting enzyme inhibitors, intensive control of blood pressure) and how to best utilize revascularization (which patients and when) remain to be defined.