Revascularization in atherosclerotic renal artery disease

Atherosclerotic-nephropathy: an updated narrative review

The increased prevalence of chronic kidney disease (CKD) in elderly patients recognizes, as main cause, the long-term exposure to atherosclerosis and hypertension. Chronic ischemic damage due to critical renal arterial stenosis induces oxidative stress and intra-renal inflammation, resulting in fibrosis and microvascular remodelling, that is the histological picture of atherosclerotic renal vascular disease (ARVD). The concomitant presence of a long history of hypertension may generate intimal thickening and luminal narrowing of renal arteries and arterioles, glomerulosclerosis, interstitial fibrosis and tubular atrophy, more typically expression of hypertensive nephropathy. These complex mechanisms contribute to the development of CKD and the progression to End Stage Kidney Disease. In elderly CKD patients, the distinction among these nephropathies may be problematic; therefore, ischemic and hypertensive nephropathies can be joined in a unique clinical syndrome defined as atherosclerotic nephropathy. The availability of novel diagnostic procedures, such as intra-vascular ultrasound and BOLD-MRI, in addition to traditional imaging, have opened new scenarios, because these tools allow to identify ischemic lesions responsive to renal revascularization. Indeed, although trials have deflated the role of renal revascularization on the renal outcomes, it should be still used to avoid dialysis initiation and/or to reduce blood pressure in selected elderly patients at high risk. Nonetheless, lifestyle modifications (smoking cessation, increased physical activity), statins and antiplatelet use, as well as cautious use of renin-angiotensin system inhibitors, remain the main therapeutic approach aimed at slowing the renal damage progression. Mesenchymal stem cells and Micro-RNA are promising target of anti-fibrotic therapy, which might provide potential benefit in ARVD patients, though safety and efficacy profile in humans is unknown too.

Kidney microcirculation response to adenosine stimulation in renal artery stenosis

The purpose of this study was to assess the vasoconstrictive effects of adenosine in the kidney microcirculation in hypertensive patients with renal artery stenosis (RAS). Twelve patients with resistant hypertension and moderate RAS were selected for the study. In all patients, systolic, diastolic and mean translesional pressure gradients, distal pressure (Pd), aortic pressure (Pa) and Pd/Pa ratio were measured using a pressure guidewire at baseline and after intrarenal bolus administration of 400 μg adenosine. We observed significant changes in mean translesional pressure gradient and systolic Pd after pharmacological stimulation. The results suggest that in hypertensive patients with RAS, vasomotor activity of the kidney microcirculation may be preserved.

Determinations of renal cortical and medullary oxygenation using blood oxygen level-dependent magnetic resonance imaging and selective diuretics

OBJECTIVE

This study was undertaken to test the hypothesis that blood O2 level-dependent magnetic resonance imaging (BOLD MRI) can detect changes in cortical proximal tubule (PT) and medullary thick ascending limb of Henle (TAL) oxygenation consequent to successive administration of furosemide and acetazolamide (Az). Assessment of PT and TAL function could be useful to monitor renal disease states in vivo. Therefore, the adjunct use of diuretics that inhibit Na reabsorption selectively in PT and TAL, Az and furosemide, respectively, may help discern tubular function by using BOLD MRI to detect changes in tissue oxygenation.

MATERIAL AND METHODS

BOLD MRI signal R2* (inversely related to oxygenation) and tissue oxygenation with intrarenal O2 probes were measured in pigs that received either furosemide (0.05 mg/kg) or Az (15 mg/kg) alone, Az sequentially after furosemide (n = 6 each, 15-minute intervals), or only saline vehicle (n = 3).

RESULTS

R2* decreased in the cortex of Az-treated and medulla of furosemide-treated kidneys, corresponding to an increase in their tissue O2 assessed with probes. However, BOLD MRI also showed decreased cortical R2* following furosemide that was additive to the Az-induced decrease. Az administration, both alone and after furosemide, also decreased renal blood flow (-26% ± 3.5% and -29.2% ± 3%, respectively, P < 0.01).

CONCLUSION

These results suggest that an increase in medullary and cortical tissue O2 elicited by selective diuretics is detectable by BOLD MRI, but may be complicated by hemodynamic effects of the drugs. Therefore, the BOLD MRI signal may reflect functional changes additional to oxygenation, and needs to be interpreted cautiously.

An isotopic diagnosis of seizure

A 22-year-old healthy woman visited our clinic for seizure and consciousness loss. A thorough history taking and physical examination was negative except for persistent high blood pressure. Serial workup for suspicious secondary hypertension revealed secondary hyperaldosteronism. Further image study showed diminished unilateral kidney size, but the computed tomographic angiogram was unremarkable. Radionuclide renography disclosed a specific pattern of compromised unilateral renal function after captopril challenge, suggesting a high probability of renal artery stenosis. Renal artery angiography finally confirmed the diagnosis, and angioplasty with stenting successfully reversed the refractory hypertension despite the shrinking kidney size. Although isotopic study is gradually fading away among our diagnostic tools, the value it demonstrates in this case warrants attention.

Atherosclerotic renovascular disease and the heart

The detrimental link between cardiac and renal pathophysiology in atherosclerotic renovascular disease (ARVD) is well described. Patients with ARVD usually have significant atherosclerotic disease in other vascular beds including the coronary circulation, and structural and functional cardiac changes are highly prevalent. This excess cardiovascular burden probably contributes to the increased cardiac morbidity and mortality seen in these patients. In this review we describe the associations of cardiovascular disease and ARVD and treatment thereof. The clinical debate of which patients are offered any additional advantage by revascularisation over medications alone remains to be answered. The close link between cardiac and renal pathophysiology in ARVD raises the possibility that renal revascularisation might confer a benefit to cardiac morphology and function. This is the subject of ongoing randomised controlled trials.

Transradial renal stenting: why and how

Transradial vascular access for invasive procedures is gaining increasingly acceptance due to reduced access-site complications and improved patient's comfort compared with transfemoral. However, the adoption of transradial access in peripheral vascular procedures is actually limited by anatomical and technical considerations. Yet, among all the peripheral vascular districts, the renal one seems to be particularly suitable for transradial approach. In this article, we discuss the rationale for preferring the radial approach instead of femoral and review the specific technical issues related to transradial renal artery stenting (RAS).

Revascularization versus medical therapy for renal-artery stenosis

BACKGROUND

Percutaneous revascularization of the renal arteries improves patency in atherosclerotic renovascular disease, yet evidence of a clinical benefit is limited.

METHODS

In a randomized, unblinded trial, we assigned 806 patients with atherosclerotic renovascular disease either to undergo revascularization in addition to receiving medical therapy or to receive medical therapy alone. The primary outcome was renal function, as measured by the reciprocal of the serum creatinine level (a measure that has a linear relationship with creatinine clearance). Secondary outcomes were blood pressure, the time to renal and major cardiovascular events, and mortality. The median follow-up was 34 months.

RESULTS

During a 5-year period, the rate of progression of renal impairment (as shown by the slope of the reciprocal of the serum creatinine level) was -0.07x10(-3) liters per micromole per year in the revascularization group, as compared with -0.13x10(-3) liters per micromole per year in the medical-therapy group, a difference favoring revascularization of 0.06x10(-3) liters per micromole per year (95% confidence interval [CI], -0.002 to 0.13; P=0.06). Over the same time, the mean serum creatinine level was 1.6 micromol per liter (95% CI, -8.4 to 5.2 [0.02 mg per deciliter; 95% CI, -0.10 to 0.06]) lower in the revascularization group than in the medical-therapy group. There was no significant between-group difference in systolic blood pressure; the decrease in diastolic blood pressure was smaller in the revascularization group than in the medical-therapy group. The two study groups had similar rates of renal events (hazard ratio in the revascularization group, 0.97; 95% CI, 0.67 to 1.40; P=0.88), major cardiovascular events (hazard ratio, 0.94; 95% CI, 0.75 to 1.19; P=0.61), and death (hazard ratio, 0.90; 95% CI, 0.69 to 1.18; P=0.46). Serious complications associated with revascularization occurred in 23 patients, including 2 deaths and 3 amputations of toes or limbs.

CONCLUSIONS

We found substantial risks but no evidence of a worthwhile clinical benefit from revascularization in patients with atherosclerotic renovascular disease. (Current Controlled Trials number, ISRCTN59586944.)

Proteinuria as a predictor of renal functional outcome after revascularization in atherosclerotic renovascular disease (ARVD)

BACKGROUND

Renal revascularization is performed in 16% of newly diagnosed patients with atherosclerotic renovascular disease (ARVD). Although there may be some improvement in hypertension control as a result of intervention, renal functional outcomes are known to vary. Pre-existing renal parenchymal injury, as manifested by proteinuria, is associated with poor functional outcome in conservatively managed ARVD patients, but this association has not been investigated in patients undergoing revascularization.

METHODS

Retrospective case note review of 83 ARVD patients who underwent renal revascularization in four centres within a renal network between 1998 and 2003 was undertaken. Amongst other parameters, baseline proteinuria was correlated with renal functional outcome post revascularization. Renal functional outcome was determined over a mean follow up of 22 months by rate of change of estimated glomerular filtration rate (eGFR) over time.

RESULTS

Univariate analysis showed that proteinuria >0.6 g/day was the only significant predictor of poor outcome after revascularization. The relationship persisted with multivariate analysis, and linear regression showed a correlation between baseline proteinuria and decline in eGFR with time (r(2) = 0.058, P = 0.039).

CONCLUSION

This study confirms that prior renal parenchymal injury, here reflected by proteinuria at baseline, is a major arbiter of renal functional outcome after renal revascularization in ARVD.

[Atherosclerotic renal artery disease management update]

In the case of atherosclerotic renal artery disease, the best conclusive results lie principally not in the degree of the stenosis but rather in the degree the renal parenchymal disease beyond the stenosis itself. These determining factors involve the controlling of the patients blood pressure, the improvement in the renal function and the beneficial results to the cardiovascular system. Besides the indispensable medical treatment, a revascularisation by angioplasty may be indicated. This procedure with or without vascular stent often allows satisfactory angiographic results. A treatment by surgical revascularisation is only recommended in the case of extensive atherosclerotic lesions of the aorta, complex lesions of the latter or an abdominal aortic aneurism. Although the frequency of restenosis of angioplasty with stent remains extremely low, the risk of cholesterol emboli due to the diffuse atherosclerotic lesions of the abdominal aorta, must be considered at the time of each aortic catheterization. The therapeutic approach of atherosclerotic renal artery disease must be dictated by the whole cardiovascular risk factors and by the threat of target organs. The control of the blood pressure and the maintenance of the renal function must be integrated in the decisional algorithm as well as the possible risks in carrying out an eventual revascularisation procedure. Finally, the renal angioplasty should in numerous situations be integrated in the overall assumption of responsibility of the atherosclerotic vascular diseases, and should be part of the medical treatment. Several questions still do exist; at what moment an atherosclerotic renal artery stenosis should and e considered critical, and which procedure should be considered for which patient? The purpose of this review is to propose a decisional tool for individualized treatments in the light of results from randomized and controlled studies.

Treatment of renovascular hypertension by transluminal angioplasty--13 years experience in a single centre

OBJECTIVE

The study is a follow-up on treatment of renovascular hypertension (RVH) with percutaneous transluminal renal angioplasty (PTRA).

METHODS

Patients were screened on the basis of clinical criteria of increased probability of RVH with renography and in selected cases with renal vein renin measurements. A positive work-up suggesting a functionally important renal artery stenosis led to renal angiography and PTRA if stenosis was confirmed; in 59%, an intravascular stent was inserted.

RESULTS

Outcome of treatment was classified as follows - group I: normotensive without medication; group II: with improved control of blood pressure; group III: unchanged blood pressure control. Grouping was performed immediately after treatment, at 1 month, 6 months and at the latest follow-up. One hundred-and-twenty-two patients (124 atherosclerotic and 12 fibromuscular lesions) were treated during 13 years. Immediately after PTRA the patients were grouped as follows - I: 31%, II: 59%, III: 10%. At 1 month, I: 13%, II: 72%, III: 15%; at 6 months, I: 11%, II: 74%, III: 15%, and at the latest follow-up, I: 11%, II: 78%, III: 11%. There were few significant complications, and renal function remained on average stable.

CONCLUSION

PTRA is an effective treatment of RVH in patients selected by signs of a flow-restricting stenosis. Twelve percent were normotensive after angioplasty and a further 77% had better controlled hypertension. Few complications were seen and renal function was on average unchanged as measured by serum creatinine.

Renal Artery Stenosis in Swine: Feasibility of MR Assessment of Renal Function during Percutaneous Transluminal Angioplasty

PURPOSE

To prospectively test--in a swine model of renal artery stenosis (RAS)--the hypothesis that magnetic resonance (MR) imaging can reveal changes in renal function at the time of percutaneous transluminal angioplasty (PTA).

MATERIALS AND METHODS

In this animal care and use committee-approved study, high-grade unilateral RAS was surgically induced in six pigs. MR imaging at 3.0 T was used for intraprocedural assessment of the anatomic and physiologic changes induced by x-ray-guided PTA. With use of MR imaging, changes in single-kidney glomerular filtration rate, extraction fraction, and renal blood flow were assessed during PTA. The arterial diameter of stenosis before and after PTA was assessed by using conventional digital subtraction angiography. Mean changes in functional and anatomic parameters were compared by using the Wilcoxon signed rank test (alpha = .05).

RESULTS

At digital subtraction angiography, the mean percentage of stenosis was 69% +/- 10 (standard deviation) before PTA and 26% +/- 10 after PTA (P<.03). Mean pre- and post-PTA extraction fraction values were 0.11 +/- 0.03 and 0.19 +/- 0.06, respectively (P<.03). The mean single-kidney glomerular filtration rate before PTA, 19 mL/min +/- 13, increased to 41 mL/min +/- 33 after PTA (P<.03). There was no significant change in mean renal blood flow after PTA (P=.44).

CONCLUSION

In swine, MR imaging can reveal changes in renal function after x-ray-guided PTA for unilateral RAS.

Controversies in renal artery stenosis: a review by the American Society of Nephrology Advisory Group on Hypertension

Renovascular hypertension is a recognized secondary potentially curable cause of hypertension since the work of Harry Goldblatt. Operative treatments for renal artery stenosis (RAS) have been offered for decades and percutaneous interventions have been widely available for 20 years. Stenting has largely obviated recurrence and modern techniques have contributed greatly to the safety of the procedure. Nevertheless, controversy abounds and prospective randomized trials have not successfully documented the value of intervention in patients with atherosclerotic RAS. The patient population has also changed remarkably. Whereas earlier patients with RAS were identified on clinical grounds, RAS is now commonly found serendipitously during angiography for other reasons. Whether or not these patients benefit from 'drive by' stenting is unknown. The practice may be hazardous and should be critically examined. A dialog and closer cooperation between cardiologists and nephrologists is warranted and organized programs should be formulated to address this problem.

Renal artery stenosis and accelerated atherosclerosis: which comes first?

Renal artery stenosis (RAS) is usually observed in hypertensive patients with extensive atherosclerosis. There is some evidence that in these patients the atherosclerotic process and the consequent target-organ damage is more severe than in hypertensive patients without RAS. In this review we will entertain the hypothesis that some of the humoral factors that are activated by RAS may contribute to accelerate the progression of atherosclerosis. Several studies identified RAS as a predictor of cardiovascular events in high-risk patients, although in most cases the contribution of blood pressure per se to the progression of vascular lesions could not be determined. As a result of experimental RAS, hypertension and increased oxidative stress are stimuli for atherosclerosis as well as cardiac and renal damage. In the presence of RAS, the renin-angiotensin system is stimulated, and it has been shown that angiotensin II exerts proinflammatory, pro-oxidant and procoagulant activities in experimental models and humans. The potential contribution of reactive oxygen species to the prohypertensive and proatherosclerotic effects of RAS is supported by evidence that nicotinamide adenine dinucleotide phosphate, reduced form oxidase is specifically stimulated by angiotensin II, an activity not shared by epinephrine. Moreover, angiotensin II triggers the release of aldosterone, endothelin 1, thromboxane A2 and other derivatives of the arachidonic acid metabolism, all of which can further and independently aggravate cardiovascular damage. Epidemiological and experimental evidence so far available suggests that accelerated atherosclerosis can be both the cause and the consequence of RAS.

The heart in renovascular disease—An association demanding further investigation

A close relationship exists between cardiovascular and renal disease; they often occur concomitantly, and abnormalities in either system are pathophysiologically important in both causing disease and determining clinical outcome in the other. Whilst the main focus of the article relates to the adverse association between atherosclerotic renovascular disease (ARVD) and the cardiovascular system, it is important to briefly review relevant epidemiology.

MR-derived renal morphology and renal function in patients with atherosclerotic renovascular disease

Appropriate selection of patients with atherosclerotic renovascular disease (ARVD) for revascularization might be improved if accurate non-invasive investigations were used to assess severity of pre-existing parenchymal damage. The purpose of this study was to evaluate the associations between magnetic resonance imaging (MRI)-measured renal morphological parameters and single-kidney glomerular filtration rate (GFR) in ARVD. Three-dimensional (3D)-MRI was performed on 35 ARVD patients. Renal bipolar length (BL), parenchymal volume, parenchymal (PT), and cortical thicknesses (CT) were measured in 65 kidneys. Thirteen kidneys were supplied by normal vessels, 13 had insignificant (<50%) renal artery stenosis (RAS), 33 significant (>or=50%) RAS, and six complete vessel occlusion. All patients underwent radioisotopic measurement of single-kidney GFR (isoSK-GFR). Overall, 3D parameters such as parenchymal volume were better correlates of isoSK-GFR (r=0.86, P<0.001) than BL (r=0.78, P<0.001), PT (r=0.63, P<0.001) or CT (r=0.60, P<0.001). Kidneys with >or=50% RAS did show significant reduction in mean CT compared to those supplied by normal vessel (5.67+/-1.63 vs 7.28+/-1.80 mm, P=0.002; 22.1% reduction) and an even greater loss of parenchymal volume (120.65+/-47.15 vs 179.24+/-86.90 ml, P<0.001; 32.7% reduction) with no significant reduction in BL. In a proportion of >or=50% RAS kidneys, a disproportionately high parenchymal volume to isoSK-GFR was observed supporting a concept of 'hibernating parenchyma'. 3D parameters of parenchymal volume are stronger correlates of isoSK-GFR than two-dimensional measures of BL, PT or CT. 3D morphological evaluation together with isoSK-GFR might be useful in aiding patient selection for renal revascularization. Kidneys with increased parenchymal volume to SK-GFR might represent a subgroup with the potential to respond beneficially to angioplasty.

A Study on the Outcome of Percutaneous Transluminal Renal Angioplasty in Patients with Renal Failure

BACKGROUND

The indications for percutaneous transluminal renal angioplasty (PTRA) in renovascular disease, as well as its benefits, remain a matter of debate. The aim of this study was to evaluate the outcome of angioplasty and to identify risk factors associated with less successful outcomes in patients with atheromatous renal artery stenosis and renal failure of varying degrees.

METHODS

The results of PTRA were analyzed retrospectively in 144 patients with serum creatinine levels of >130 micromol/l. Patients were divided into 5 groups according to their indication for angioplasty: (1) deteriorating renal function; (2) accelerating hypertension; (3) a combination of 1 and 2; (4) peripheral vascular disease, and (5) miscellaneous conditions.

RESULTS

The baseline mean (+/- SD) systolic and diastolic blood pressures of the entire group were lowered from 180 +/- 32 and 95 +/- 16 mm Hg to 162 +/- 23 and 86 +/- 12 mm Hg, respectively (p < 0.0005), 12 months after angioplasty. The blood pressure level was unaffected by angioplasty in patients with claudication. The mean number of antihypertensive drugs was reduced in the group with accelerating hypertension from 2.9 +/- 0.8 to 2.4 +/- 1.2 (p = 0.019), and in the group with unilateral renal artery stenosis and two kidneys from 2.4 +/- 1.0 to 1.8 +/- 1.1 (p = 0.002), 12 months after PTRA. Glomerular filtration rate at 3-month follow-up had increased from 23 +/- 11 to 27 +/- 14 ml/min/1.73 m(2) (p = 0.021) in group 1, from 25 +/- 11 to 28 +/- 14 ml/min/1.73 m(2) (p = 0.031) in the combined group of patients consisting of groups 1 and 3, and from 32 +/- 13 to 35 +/- 14 ml/min/1.73 m(2) (p = 0.019) in the group with unilateral renal artery stenosis. No statistically significant difference was found in any of these 3 groups 1 year after angioplasty. The first patient group had an increased prevalence of cardiovascular disease, aortic aneurysm, carotid occlusive disease, and peripheral vascular disease compared to the other patient groups (p < 0.05). Patients with baseline creatinine levels of >300 micromol/l had a lower survival rate at 12, 60, and 120 months after PTRA than patients with serum creatinine levels of <300 micromol/l (p < 0.005). Survival was also lower in patients with bilateral renal artery stenosis and those with a single kidney, compared to patients with a unilateral stenosis at both 5 and 10 years after PTRA (p < 0.05). Regression analysis of predictor variables of mortality rate showed that the relative risk (RR) associated with increased serum creatinine was 4.7 (CI 2.0-11.0; p < 0.0005). The RR for older patients was 1.1 (CI 1.0-1.2; p = 0.008), and the RR for former smokers was 6.0 (CI 1.6-24.0; p = 0.009).

CONCLUSION

The results of the present study indicate that glomerular filtration can be improved in patients who primarily undergo angioplasty to rescue renal function. Renal function with creatinine levels of >300 micromol/l was associated with a lower survival rate. It is, therefore, possible that patients selected after a thorough evaluation of their renal function and comorbid disease factors may benefit from PTRA, even when the indication for angioplasty is to salvage renal function.

Value of Doppler sonography for predicting clinical outcome after renal artery revascularization in atherosclerotic renal artery stenosis

OBJECTIVE

The purpose of this study was to prospectively evaluate the usefulness of Doppler sonography for predicting blood pressure and renal function improvement after percutaneous renal angioplasty in patients with unilateral atherosclerotic renal artery stenosis.

METHODS

Thirty-six patients with successfully revascularized unilateral atherosclerotic renal artery stenosis were included. Patients were evaluated by Doppler sonography before treatment, with the resistive index (RI) and acceleration being measured in both kidneys. Blood pressure, number of antihypertensive drugs, and serum creatinine concentration were assessed before treatment and thereafter during a 23 +/- 15-month (mean +/- SD) period.

RESULTS

In 20 of the 36 patients (55%), the RI was less than 0.80 before revascularization. After treatment, blood pressure improved in 17 (85%) of those 20 patients and improved in 8 (50%) of 16 patients with an RI of greater than 0.80 (P < .05). Twenty-five patients had renal insufficiency pretreatment, and 11 (44%) had a baseline RI of less than 0.80. Improvement in renal function after angioplasty was shown in 5 (45%) of these 11 patients and in 4 (28.5%) of 14 in the group with high RI (P > .05, not significant). On analysis of acceleration, blood pressure improved in 9 (69%) of 13 patients with acceleration of greater than 3 m/s(2) and in 16 (69.5%) of 23 with acceleration of less than 3 m/s(2) (P > .05). In patients with renal insufficiency, 5 (50%) of 10 cases with normal baseline acceleration and 4 (27%) of 15 with low acceleration showed improvement in renal function (P > .05).

CONCLUSIONS

An elevated RI should not exclude patients from a revascularization procedure because, although renal RI does correlate with blood pressure response to revascularization, it is not a useful parameter in predicting renal function outcome. Acceleration has no prognostic value.

[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.

Atherosclerotic renovascular disease in United States patients aged 67 years or older: Risk factors, revascularization, and prognosis

BACKGROUND

Although atherosclerotic renovascular disease is increasingly recognized in chronic kidney disease, few national level studies have examined its clinical epidemiology.

METHODS

Claims data from a 5% random sample of the United States Medicare population were used to select patients without atherosclerotic renovascular disease in the 2 years preceding December 31, 1999 (N= 1,085,250), followed until December 31, 2001.

RESULTS

The incidence of atherosclerotic renovascular disease was 3.7 per 1000 patient-years. Major antecedent associations [P < 0.05, with adjusted hazards ratios (HR) > 1.5] included chronic kidney disease (adjusted HR 2.54), hypertension (2.42), peripheral vascular disease (2.00), and atherosclerotic heart disease (1.70). Adverse event rates after incident atherosclerotic renovascular disease greatly exceeded those in the general population (P < 0.0001): atherosclerotic heart disease, 303.9 per 1000 patient-years (vs. 73.5 in the general population); peripheral vascular disease, 258.6 (vs. 52.2); congestive heart failure, 194.5 (vs. 56.3); cerebrovascular accident or transient ischemic attack, 175.5 (vs. 52.9); death, 166.3 (vs. 63.3); and renal replacement therapy, 28.8 (vs. 1.3). Among atherosclerotic renovascular disease patients, 16.2% underwent a renal revascularization procedure, percutaneously in 96%. Revascularization was not associated with renal replacement therapy, congestive heart failure, or death but was associated with atherosclerotic heart disease (adjusted HR 1.42) (P= 0.004) and peripheral vascular disease (adjusted HR 1.38) (P= 0.002).

CONCLUSION

Atherosclerotic renovascular disease is strongly associated with cardiovascular disease, both past and future. Absolute cardiovascular risk exceeds that of renal replacement therapy. Renal revascularization is used selectively and shows inconsistent associations with cardiovascular outcomes, renal replacement therapy, and death.

Renal artery stenosis of solitary kidney: the dilemma

BACKGROUND

Renal artery stenosis is an important cause of hypertension and renal failure. When present in a solitary kidney, it is associated with extremely high morbidity and mortality. Although guidelines suggest an aggressive approach by revascularization in these cases, available evidence is too weak and contradictory to provide definite recommendations for treatment.

OBJECTIVES

To discuss the various clinical factors predicting the benefit from revascularization.

METHODS AND RESULTS

Review of more recent clinical trials is presented.

DISCUSSION

The approach to the patient with single kidney and renal artery stenosis is discussed and, although there is insufficient evidence-based medicine for guidelines, some suggestions are made to predict revascularization results in these cases.

CONCLUSION

Continuous development of clinical prediction rules will help in the management of renal artery stenosis of solitary kidney.

Endovascular Therapy of Renal Artery Stenosis: Where Do We Stand Today?

Angioplasty and stent therapy for stenoses of the renal artery have long been part of the everyday life of interventional radiologists. Newer studies, however, challenge the clinical significance of the method. A decisive advantage of endovascular techniques for the treatment of arterial hypertension as opposed to therapy with modern antihypertensives could not be proven in individual randomized studies, even though blood pressure control was observed to be facilitated by PTA (percutaneous transluminal angioplasty). Renal function often did not show any sustainable improvement following elimination of the renal artery stenosis. However, progression of kidney insufficiency could be slowed down. There is still no general justification from the existing data for the treatment of incidental stenoses. Many questions remain open regarding the technique. Whereas fibromuscular dysplasia can be treated by balloon angioplasty as a general rule, a metallic endoprosthesis must often be used for atherosclerotic stenoses. The outstanding morphologic results of stent therapy in the short and medium term course are often simply used to justify primary stent implantation in ostial stenoses.

Dilemmas in the management of renal artery stenosis

Atherosclerotic renovascular disease (ARVD) accounts for >90% of renal artery stenosis (RAS) in Western populations; the remainder are due to fibromuscular disease (FMD). The epidemiology is quite different in the Indian subcontinent and the Far East where Takayasu's arteritis may be responsible for up to 60% of RAS cases. ARVD is very commonly associated with hypertension and renal dysfunction; it is a disease of ageing and is frequently observed in association with other vascular diseases. There is increasing evidence that in patients with ARVD and chronic renal dysfunction the aetiology of the latter is more often due to long-standing intra-renal vascular disease and parenchymal injury than to reversible ischaemia. This is reflected in the variability in renal functional outcome following revascularization, with an improvement in renal function being observed in only a minority of patients; the majority show no apparent change or even a decline in renal function. A major current challenge concerns the identification of patients who are likely to benefit from renal revascularization procedures, but technological advances in imaging offer potential in aiding this selection. Large-scale randomized controlled trials are required to determine the overall effects of renal artery intervention and, more specifically, to help identify which subgroups of patients will benefit from revascularization.

The contrast-enhanced Doppler ultrasound with perfluorocarbon exposed sonicated albumin does not improve the diagnosis of renal artery stenosis compared with angiography

There are no studies investigating the effect of the contrast infusion on the sensitivity and specificity of the main Doppler criteria of renal artery stenosis (RAS). Our aim was to evaluate the accuracy of these Doppler criteria prior to and following the intravenous administration of perfluorocarbon exposed sonicated albumin (PESDA) in patients suspected of having RAS. Thirty consecutive hypertensive patients (13 males, mean age of 57 +/- 10 years) suspected of having RAS by clinical clues, were submitted to ultrasonography (US) of renal arteries before and after enhancement using continuous infusion of PESDA. All patients underwent angiography, and haemodynamically significant RAS was considered when >or=50%. At angiography, it was detected RAS >or=50% in 18 patients, 5 with bilateral stenosis. After contrast, the examination time was slightly reduced by approximately 20%. In non-enhanced US the sensitivity was better when based on resistance index (82.9%) while the specificity was better when based on renal aortic ratio (89.2%). The predictive positive value was stable for all indexes (74.0%-88.0%) while negative predictive value was low (44%-51%). The specificity and positive predictive value based on renal aortic ratio increased after PESDA injection respectively, from 89 to 97.3% and from 88 to 95%. In hypertensives suspected to have RAS the sensitivity and specificity of Duplex US is dependent of the criterion evaluated. Enhancement with continuous infusion of PESDA improves only the specificity based on renal aortic ratio but do not modify the sensitivity of any index.

Seventh report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure

The National High Blood Pressure Education Program presents the complete Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure. Like its predecessors, the purpose is to provide an evidence-based approach to the prevention and management of hypertension. The key messages of this report are these: in those older than age 50, systolic blood pressure (BP) of greater than 140 mm Hg is a more important cardiovascular disease (CVD) risk factor than diastolic BP; beginning at 115/75 mm Hg, CVD risk doubles for each increment of 20/10 mm Hg; those who are normotensive at 55 years of age will have a 90% lifetime risk of developing hypertension; prehypertensive individuals (systolic BP 120-139 mm Hg or diastolic BP 80-89 mm Hg) require health-promoting lifestyle modifications to prevent the progressive rise in blood pressure and CVD; for uncomplicated hypertension, thiazide diuretic should be used in drug treatment for most, either alone or combined with drugs from other classes; this report delineates specific high-risk conditions that are compelling indications for the use of other antihypertensive drug classes (angiotensin-converting enzyme inhibitors, angiotensin-receptor blockers, beta-blockers, calcium channel blockers); two or more antihypertensive medications will be required to achieve goal BP (<140/90 mm Hg, or <130/80 mm Hg) for patients with diabetes and chronic kidney disease; for patients whose BP is more than 20 mm Hg above the systolic BP goal or more than 10 mm Hg above the diastolic BP goal, initiation of therapy using two agents, one of which usually will be a thiazide diuretic, should be considered; regardless of therapy or care, hypertension will be controlled only if patients are motivated to stay on their treatment plan. Positive experiences, trust in the clinician, and empathy improve patient motivation and satisfaction. This report serves as a guide, and the committee continues to recognize that the responsible physician's judgment remains paramount.

Evaluation of the patients with renovascular hypertension after percutaneous revascularization by Doppler ultrasonography

OBJECTIVE

Evaluation of the effectiveness of percutaneous revascularization is based primarily on clinical criteria, and laboratory findings rather than direct investigation of luminal width. The purpose of this study was to evaluate the success of endovascular revascularization with serial Doppler ultrasound (US) examinations.

METHODS AND MATERIAL

19 patients (14 were atherosclerotic, five were with fibromuscular dysplasia) with suspected renovascular hypertension treated by percutaneous revascularization were included in a prospective study. Patients had 23 renal artery stenoses reducing the diameter by more than 50%. Doppler US examinations were performed before intervention, and 1 day, 3 and 6 months after intervention.

RESULTS

Initial revascularization was technically successful in 21 of 23 stenoses (91.3%) (18 PTRA, three stent placement). Hypertension was cured in five atherosclerotic and in five fibromuscular dysplasia (FMD) patients, and improved in four atherosclerotic patients. Residual stenosis was determined in six patients and the others were evaluated as normal by initial postprocedure Doppler US. As based on Doppler US, restenosis (>60%-narrowing) was depicted in four of six (66.6%) renal arteries with residual stenosis, and one of 15 (6.6%) normal renal arteries at 1 year. This difference in restenosis rates (residual stenosis vs. normal) was significant (P<0.05).

CONCLUSION

Positive predictor for recurrence was a residual renal artery stenosis documented by Doppler US 1 day after percutaneous revascularization in atherosclerotic cases.

Renal function and outcome of PTRA and stenting for atherosclerotic renal artery stenosis

BACKGROUND

Prior studies of percutaneous transluminal renal artery angioplasty and stenting (PTRAS) for atherosclerotic renal artery stenosis (RAS) have shown that renal function is improved in about 25%, stabilizes in about 40%, but worsens in about 25% of patients. The factors predicting benefit remain controversial. We tested the hypothesis that the baseline glomerular filtration rate (GFR) predicts the changes in GFR and blood pressure (BP) after PTRAS.

METHODS

Treated hypertensive patients with positive renal color-coded duplex Doppler velocimetry and clinical criteria were screened by arteriography. Patients (N = 105) were included if they had an RAS >or=70%, a transluminal pressure gradient >or=30 mm Hg and, they had more than 100 days of follow-up. GFR was calculated from the serum creatinine concentration (SCr). Patients were divided by baseline GFR into subgroups with normal to mildly impaired (N = 52) or moderately to severely impaired (N = 53) initial GFR, according to a GFR >or=50 or <50 mL. min-1 respectively. All received PTRAS.

RESULTS

For the entire group, after a mean follow-up period of 371 days, there were significant reductions in systolic and diastolic BP (before, 160 +/- 26/91 +/- 12 vs. after, 145 +/- 20/83 +/- 10 mm Hg, respectively; mean +/- SD; P < 0.0001), and a modest increase in the calculated GFR (before, 54 +/- 26 vs. after, 62 +/- 28 mL. min-1; mean +/- SD; P < 0.007). However, in the subgroup of patients with an initially lower GFR there was a significant increase in the calculated GFR (from 33.3 +/- 10 to 54 +/- 24 mL. min-1; mean +/- SD; P < 0.0001) despite no significant change in BP (161 +/- 27/90 +/- 12 vs. 151 +/- 21/86 +/- 12; P = NS). In contrast, in the subgroup with an initially higher GFR, there were significant (P < 0.0001) reductions in systolic BP (from 159 +/- 25 to 138 +/- 16 mm Hg) and diastolic BP (from 91 +/- 11 to 81 +/- 9 mm Hg), but no significant change in the calculated GFR (from 75 +/- 21 to 70.2 +/- 30 mL. min-1; P = NS). The significance of GFR variation in subgroups remained after correction of baseline data to exclude the influence of the expected regression to the mean.

CONCLUSIONS

Patients with atherosclerotic RAS fulfilling strict criteria of severity may have significant improvements in BP one year after PTRAS but only modest in GFR. The initial GFR may anticipate whether the benefits in the outcome will be in renal function enhancement (those with an initially depressed GFR) or in hypertension control (those with an initially normal or mildly impaired GFR).

Treatment of acute renal failure caused by renal artery occlusion with renal artery angioplasty

BACKGROUND

Renovascular disease is a common cause of renal impairment and hypertension, particularly in the older population. Oligoanuric acute renal failure secondary to renal artery occlusion is not well recognized; however, it is potentially reversible if identified and treated.

METHODS

Five patients presented to our institution with oligoanuric acute renal failure. Each had evidence of vascular disease, and a prerenal insult was identified. They were investigated with renal artery Doppler ultrasound or nuclear imaging before proceeding to percutaneous angioplasty and stent placement.

RESULTS

The targeted kidney had relatively well-preserved renal size, and potential viability of the renal tissue was determined by nuclear scanning with parenchymal uptake of tracer. Percutaneous angioplasty and stent placement resulted in brisk reperfusion of the kidney and an immediate diuresis with improvement of renal function, avoiding supportive dialysis after the procedure. Contrast nephrotoxicity was identified in two of the five cases.

CONCLUSION

Renal artery occlusion should be considered as a cause of oliguric acute renal failure, particularly in patients at high risk who present with a sudden deterioration of renal function, with nuclear imaging showing potentially viable renal tissue with relatively well-preserved renal size. Percutaneous revascularization should be considered in this group.

Prevalence and outcome of renal artery stenosis in atherosclerotic patients with renal dysfunction

We investigated the prevalence of renal artery disease and outcome in a cohort of atherosclerotic patients with renal dysfunction. We studied 44 consecutive patients who were older than 50 years of age, who had renal dysfunction and in whom one or more of the following atherosclerotic diseases was confirmed: cerebral infarction, coronary artery disease or peripheral vascular disease. Renal artery stenosis was assessed by gadolinium-enhanced magnetic-resonance angiography. Patients who were treated medically were prospectively followed up in our outpatient clinic and the impact of renal artery stenosis on survival was evaluated. Renal artery stenosis was found in 22 (50%) of the 44 patients. Difference in kidney length and carotid artery stenosis were identified as independent predictors of renal artery stenosis. Among the patients who were treated medically (n=42), rates of mortality were 4.4, 12.7 and 18.1 per 100 patient-years in those without renal artery stenosis, those with unilateral renal artery stenosis and those with bilateral renal artery stenosis, respectively. The mortality and renal survival curves were significantly different among these three groups. These findings indicate that renal artery stenosis is common in patients with renal dysfunction and concomitant cardiovascular disease, especially in those with carotid artery stenosis, and that a substantial difference in the length of kidneys may be a predictor of renovascular disease. Patients with renal dysfunction resulting from renal artery stenosis are at risk of death from cardiovascular disease and end-stage renal failure.

Noninvasive measurement of extraction fraction and single-kidney glomerular filtration rate with MR imaging in swine with surgically created renal arterial stenoses

PURPOSE

To test whether magnetic resonance (MR) imaging enables accurate measurement of extraction fraction (EF) in swine with unilateral renal ischemia and to evaluate effects of renal arterial stenosis on EF and single-kidney glomerular filtration rate.

MATERIALS AND METHODS

High-grade unilateral renal arterial stenoses were surgically created in eight pigs. Direct measurements of renal venous and arterial inulin concentration provided reference standard estimates of single-kidney EF. Pigs were imaged with a 1.5-T imager to estimate EF, renal blood flow, and glomerular filtration rate. A breath-hold inversion-recovery spiral sequence was used to measure T1 of blood in the infrarenal inferior vena cava and renal veins after intravenous administration of gadopentetate dimeglumine, and these data were used to calculate EF. Cine-phase contrast material-enhanced imaging of the renal arteries provided quantitative renal blood flow measurements. Bilateral single-kidney glomerular filtration rate was then determined: glomerular filtration rate = renal blood flow x (1 - hematocrit level) x EF.

RESULTS

A statistically significant linear correlation was found between EF, as determined with MR imaging, and inulin (r = 0.77). As compared with kidneys without renal arterial stenosis, kidneys with renal arterial stenosis showed 50% (0.14/0.28) EF reduction (P <.01) and 59% glomerular filtration rate reduction (P <.01).

CONCLUSION

MR imaging shows promise for in vivo measurement of EF and glomerular filtration rate, which may be useful in assessing the clinical importance of renal arterial stenosis.

Incidental renal artery stenosis among a prospective cohort of hypertensive patients undergoing coronary angiography

OBJECTIVE

To determine the feasibility, safety, and clinical yield of angiographic screening among hypertensive patients undergoing coronary angiography.

PATIENTS AND METHODS

This study was a prospective cohort analysis of hypertensive patients who underwent cardiac catheterization at a tertiary care referral center from July 1998 to March 1999. Abdominal aortography was performed to screen for renal artery stenosis, the percentage of which was measured.

RESULTS

The mean +/- SD age of the 297 study patients was 64.9+/-10.2 years; 58.6% were male, and 98.0% were white. Mean +/- SD systolic/diastolic blood pressure was 142.8+/-22.5/79.6+/-11.4 mm Hg. Aortography required a mean incremental dose of 62+/-9 mL of nonionic contrast agent. No complications were attributable to aortography. Of 680 renal arteries, 611 (90%) were visualized adequately. Also, 53% of patients had normal renal arteries, 28% had stenoses less than 50%, and 19.2% had stenoses of 50% or more. Renal artery stenosis was bilateral in 3.7% of patients and high grade (>70% stenosis) in 7%. Patients with renal artery stenosis were more likely to have had a previous coronary intervention. In multivariate analysis, systolic blood pressure (odds ratio [OR], 1.2; 95% confidence interval [CI], 1.03-138; P=.02), history of stroke or transient ischemic attack (OR, 2.7; 95% CI, 1.27-5.78; P=.01), and cancer (OR, 2.0; 95% CI, 1.02-3.82; P=.04) independently correlated with renal artery stenosis of 50% or more.

CONCLUSION

The prevalence of incidental renal artery stenosis among hypertensive patients undergoing coronary catheterization is significant. Therefore, screening abdominal aortography should be considered in these patients to better define their risk of cardiovascular complications.

Cortical thickness: an early morphological marker of atherosclerotic renal disease

BACKGROUND

Although kidney size is still the most commonly used morphological parameter, it is not sensitive enough for early detection of atherosclerotic renal disease (ARD). The purpose of this work was to evaluate morphological abnormalities on both post-stenotic and contralateral kidneys, by using spiral computed tomography angiography (CTA).

METHODS

Spiral CTA was performed in 49 hypertensive patients. Renal diameters, renal length, and cortical thickness were measured in 26 post-stenotic kidneys, 26 contralateral kidneys and 46 control kidneys. Mean cortical thickness, cortical area, and medullary length were calculated.

RESULTS

The right and left control kidneys were of comparable morphology. The post-stenotic kidneys showed significant cortical atrophy. The contralateral kidneys also underwent cortical disease, as judged by comparison with control kidneys. A threshold of 800 mm2 was identified for the cortical area that allowed us to distinguish control kidneys from post-stenotic kidneys. Similarly, a threshold of 8 mm was identified for mean cortical thickness. Renal length was still within normal range in all kidney groups. The measurement of superior pole segments appeared to be more sensitive than measurement at other locations for identifying significant intrarenal lesions. There was no significant correlation between clinical and morphological parameters.

CONCLUSIONS

These results suggest that cortical parameters are more sensitive for early diagnosis of ARD than kidney size. Cortical atrophy should be a useful marker for guidance for revascularization.

Epidemiology of renal dysfunction and patient outcome in atherosclerotic renal artery occlusion

Patients with atherosclerotic renal artery occlusion (RAO) effectively have only a single functioning kidney, so they constitute an ideal group in whom to study the relationship of atherosclerotic renovascular disease (ARVD) severity to renal functional outcome. Of 299 patients with ARVD who had presented to a single center over a 12-yr period, 142 (47.5%) patients with RAO were identified. There was no relationship between baseline renal function and contralateral renovascular anatomy. Patients with contralateral normal, insignificant (<50%), or significant (>50%) renal artery stenoses had baseline creatinine of 243 +/- 235, 292 +/- 197, or 210 +/- 102 micromol/L, respectively, but patients with bilateral RAO (creatinine, 540 +/- 304 micromol/L; P < 0.0001) were significantly worse. There were significant correlations between baseline GFR and both proteinuria (r = -0.32; P < 0.01) and contralateral bipolar renal length (r = 0.44; P < 0.0001). Over a mean follow-up period of 31 +/- 21 (2 to 82) mo, the overall rate of progressive renal functional decline was -4.1 ml/min per yr. Nine patients required dialysis at presentation and a further 15 (10.5%) during the course of the study. There were 85 (59.9%) deaths; median survival of the whole group was 25 mo, and 5-yr survival was 31%. Multivariate analysis indicated that low baseline GFR was the chief variable independently associated with increased probability of death or need of dialysis but that renal vascular anatomy had no prognostic impact. This study reinforces the importance of intrarenal vascular and parenchymal disease in the etiology of renal dysfunction in ARVD.