Atherosclerotic renal artery stenosis: from diagnosis to treatment

Renovascular Disease and Mesenteric Vascular Disease

Renal artery stenosis is caused by atherosclerosis and fibromuscular dysplasia and is associated with ischemic nephropathy, renovascular hypertension, and accelerated cardiovascular disease. Routine screening for renal artery stenosis is not recommended but is reasonable in patients who have rapid onset of hypertension, resistant hypertension, progressive renal insufficiency, recurrent pulmonary edema, or repeat admissions for heart failure. Acute mesenteric ischemia is caused by arterial embolism or thrombosis, mesenteric venous thrombosis, or nonocclusive mesenteric ischemia, whereas chronic mesenteric ischemia is most often caused by arterial obstruction. This article reviews the epidemiology, pathophysiology, diagnosis, and management of these two conditions.

HEMODYNAMIC EFFECT OF OBSTRUCTION TO RENAL ARTERIES CAUSED BY STENT GRAFTS IN PATIENTS WITH ABDOMINAL AORTIC ANEURYSMS

To investigate the hemodynamic effects of partial obstruction to the renal orifice caused by inappropriate stent-graft location. Pre-operative and deployment models of a stent graft with various degrees of obstruction to the renal orifice are constructed based on medical images of abdominal aortic aneurysm. Hemodynamics, including flow pattern, time-averaged wall shear stress (TAWSS), oscillatory shear index (OSI), as well as relative residence time (RRT) are analyzed using numerical simulations. Flow rate distributions are assessed and verified by in vitro experiments. Results show that partial blockage to the renal branch orifice leads to flow recirculation and vortices with low wall shear stress around the renal ostia, whereas OSI and RRT on the renal arteries increase with the degree of obstruction. While the in vitro experiment indicates a decreasing flow rate to the bilateral renal arteries as renal artery ostia are obstructed. In conclusion, obstruction to the renal arteries induced by an inappropriate stent graft location causes stenosis in the renal artery in the long term. This study reveals a possible pathological mechanism of renal complications due to the implantation of a stent graft.

Clinical Use of Laboratory Tests for the Identification of Secondary Forms of Arterial Hypertension

The prevalence of secondary hypertension can be underestimated if appropriate tests are not performed. The importance of selecting patients with a high pre-test probability of secondary forms of hypertension is first discussed. The laboratory tests currently used for seeking a cause of hypertension are critically reviewed, with emphasis on their operative features and limitations. Strategies to identify primary aldosteronism, the most frequent form of secondary hypertension, and to determine its unilateral or bilateral causes are described. Treatment entails adrenalectomy in unilateral forms, and mineralocorticoid receptor blockade in bilateral forms. Renovascular hypertension is also a common, curable form of hypertension, that should be identified as early as possible to avoid the onset of cardiovascular target organ damage. The tests for its confirmation or exclusion are discussed. The various tests available for the diagnosis of pheochromocytoma, which is much rarer than the above but extremely important to identify, are also described, with emphasis on recent developments in genetic testing. Finally, the tests for diagnosing some rarer monogenic forms and other renal and endocrine causes of arterial hypertension are explored.

Long-Term Follow-up of Renal Artery Stenting in an Australian Population

BACKGROUND

Renal artery stenosis comprises both atherosclerotic renovascular disease and fibromuscular dysplasia, and may be associated with refractory hypertension, acute 'flash' pulmonary oedema and renal failure. The long-term clinical effects of renal artery stenting remain unclear.

AIM

To assess the procedural and long-term safety and efficacy of renal artery stenting and its effect on blood pressure, antihypertensive medication usage and serum creatinine.

METHODS

All patients referred for renal artery stenting at our institution between September 1997 and December 2003 were entered into a prospectively collected database. Systolic and diastolic blood pressure, number of antihypertensive medications, serum creatinine and estimated glomerular filtration rate (eGFR) were recorded. Patients were followed-up at least six months post-procedure.

RESULTS

Eighty-nine patients underwent renal arteriography, with 110 stents deployed in 102 lesions. The procedural success rate was 99% with no procedural mortality. There were two cases of peri-procedural haemorrhage and one of sepsis. One patient developed renal and peripheral atheroemboli.

FOLLOW-UP

Mean follow-up was 28 months (range 6 months-7 years). Eight patients were lost to follow-up. There were nine deaths with a mean time to death of 20.7 months (range 12 months-3 years). There was a highly statistically significant fall in systolic blood pressure (BP) from 161.7+/-29.5 mmHg pre-procedure to 138.7+/-17.9 mmHg at long-term follow-up post-procedure (p<0.0001). The clinical restenosis rate was 6.2%. Renal function and eGFR remained stable and there was a borderline significant decrease in the number of antihypertensive medications used (p=0.05).

CONCLUSION

Renal artery stenting is safe and appears effective for the treatment of clinically significant renal artery stenosis.

Outcome of blood pressure and renal function in patients with renal artery stenosis after stenting

OBJECTIVE

To study the response of systolic and diastolic blood pressure (BP) and renal function after renal artery stenting at three months, six months, one year and last follow-up.

METHODS

Patients with significant renal artery stenosis who underwent angioplasty with stenting from January 1999 to September 2006 were analyzed. The BP and serum creatinine levels were recorded at baseline, three months, six months, one year and at last follow-up. Generalized estimating equations were applied to analyze the changes in blood pressure and serum creatinine over time.

RESULTS

There were 32 patients - 21 Chinese, six Malay and five Indian. The male to female ratio was 1.3:1. The mean age (± SD) was 69.4±8.8 years. The mean follow-up time was 1.8±1.6 years (range 0.5 to six years). When compared with the baseline BP, there was significant improvement at three months, six months, one year and at last follow-up. In the diabetes mellitus (DM) group, there was deterioration in serum creatinine. In the non-DM group, there was stabilization of serum creatinine with improvement at one year.

CONCLUSION

Significant improvement in BP occurs in renal artery stenosis patients after stenting. In patients without DM, renal function remains stable or improves. However, in DM patients, especially those with proteinuria, there is deterioration in renal function.

Prévalence des sténoses des artères rénales dépistées au cours de coronarographies diagnostiques : dans quels cas doit-on réaliser une aortographie abdominale ?

PURPOSE

To define a subgroup of patients at increased risk of renal artery stenosis (RAS) in a population of patients undergoing cardiac catheterization.

MATERIALS AND METHODS

A total of 467 patients (mean age of 64 Years +/-11) underwent cardiac catheterization and aortography Results were evaluated to detect correlations between the presence or absence of RAS and clinical and biological parameters.

RESULTS

A total of 42 (9%) patients had a renal artery stenosis. Univariate analysis defined parameters correlated with the presence of RAS: systolic blood pressure (p=0.03), pulse pressure (p=0.005), age (p<0.0001), creatinine clearance (p<0.0001), 2-vessel (p=0.028) and 3-vessel (p=0.037) coronary artery diseases. Multivariate analysis showed that the presence of RAS correlated to creatinine clearance (p=0.02) and 2-vessel coronary artery disease. A creatinine clearance between 30 and 60 ml/min and multi-vessel coronary artery disease defined a subgroup at increased risk of RAS with sensitivity, specificity, positive and negative predictive values of: 47.6, 90.1, 32.3 and 94.6%. The prevalence of renal artery stenosis was 5.2% when both parameters were absent.

CONCLUSION

Patients with mild renal insufficiency and multi-vessel coronary artery disease defined a subgroup of patients at increased risk of RAS (32.5%) that may benefit from abdominal aortography performed at the time of cardiac catheterization.

Acute renal failure in the surgical setting

Acute renal failure (ARF) is an unwelcome complication of major surgical procedures that contributes to surgical morbidity and mortality. Acute renal failure associated with surgery may account for 18-47% of all cases of hospital-acquired ARF. The overall incidence of ARF in surgical patients has been estimated at 1.2%, although is higher in at-risk groups. Mortality of patients with ARF remains disturbingly high, ranging from 25% to 90%, despite advances in dialysis and intensive care support. Appreciation of at-risk surgical populations coupled with intensive perioperative care has the capacity to reduce the incidence of ARF and by implication mortality. Developments in understanding the pathophysiology of ARF may eventually result in newer therapeutic strategies to either prevent or accelerate recovery from ARF. At present the best form of treatment is prevention. In this review the epidemiology, pathophysiology, diagnosis, treatment and possible prevention of ARF will be discussed.

[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.

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.

Renal vein renin measurements accurately identify renovascular hypertension caused by total occlusion of the renal artery

OBJECTIVE

To assess the usefulness of indexes derived from renal vein renin measurements.

DESIGN

A 12-year prospective study.

SETTING

A tertiary institutional referral centre.

PATIENTS AND METHODS

Between 1988 and 2000, we studied 152 consecutive hypertensive patients with a high pre-test probability of renovascular hypertension (RVH). RVH was diagnosed retrospectively on the basis of reduction in blood pressure after correction of ischaemia at follow-up. Renal vein renin measurements were used to calculate the ratios: Visch/Vctl (renal vein renin ratio; RVRR); Vctl/Viivc; (Visch - Viivc)/Viivc; (Vctl - Viivc)/Viivc, where Visch and Vctl indicate plasma renin activity (PRA) in the ischaemic and contralateral renal veins, respectively, and Viivc denotes PRA in the infrarenal inferior vena cava. A receiver operator characteristics (ROC) curve analysis was used to determine the cut-off value of renal vein renin measurement indexes that provided the best discrimination between patients with and without RVH and to identify patients with RVH caused by total occlusion of the renal artery.

RESULTS

Sixty-seven patients were diagnosed as having RVH: 51 had significant renal artery stenoses (RVH non-occluded) and 16 had total renal artery occlusion (RVH occluded). Of the remaining 85 patients in whom RVH was excluded (non-RVH group), 27 had reno-parenchymal hypertension and 58 had essential hypertension. Of the renal vein renin measurement indexes, only RVRR and (Visch - Viivc)/Viivc in RVH-occluded patients differed significantly (P < 0.005) from those in the non-RVH group and showed the best performance by ROC curve analysis. This analysis also showed that, at any cut-off value, RVRR was far more accurate for identification of RVH-occluded patients than for identification of RVH non-occluded patients, both in the subgroup with unilateral and, even more so, in those with bilateral renal artery lesions. The best trade-off between sensitivity and false-positive rate was provided by cut-off values of 1.55 and 1.70 of the RVRR for identification of non-occluded and occluded RVH, respectively.

CONCLUSIONS

RVRR is more useful for establishing an indication for nephrectomy in patients with renal artery occlusion than for identifying those patients with renal artery stenosis who will benefit from revascularization. In patients with RVH with bilateral renal artery lesions, lateralization of renin secretion occurs only in the presence of total renal artery occlusion. Different cut-off values are necessary for identification of non-occluded and occluded RVH.

Renal artery stenosis: a disease worth pursuing

Consider renovascular hypertension (HT) when: Newly diagnosed hypertension presents with features that are atypical of essential hypertension; Resistant hypertension is associated with risk factors for atheroma; or Angiotensin-converting enzyme (ACE) inhibitor or angiotensin-II-receptor antagonist therapy is associated with increasing plasma creatinine levels. Atheromatous renovascular HT can often be managed medically, which includes intensive correction of cardiovascular risk factors. ACE inhibitors are probably second-line antihypertensives for patients with unilateral renal artery stenosis and two kidneys. First-line antihypertensives are diuretics, beta-blockers and calcium-channel blockers. Bilateral renal artery stenosis, or a unilateral stenosis in a patient with only one kidney, is an absolute contraindication to ACE inhibition.