Clinical Evaluation of Renovascular Hypertension and Therapeutic Decisions

Renin-Dependent Hypertension Caused by Nonfocal Stenotic Aberrant Renal Arteries

We have identified 2 relatively young patients with significant hypertension, an elongated single aberrant renal artery supplying blood to a renal segment, and evidence for localization of the elevated plasma renin activity to the side and vein draining the affected kidney. Furosemide-induced diuresis and acute oral captopril stimulated the renal vein/contralateral renin ratios to 4.3:1 and 6.5:1 in patients 1 and 2, respectively. These renal vein ratios are significantly higher than normal (>3:1 under similar conditions). Partial resection of the portion of the kidney affected by the aberrant tortuous artery led to a marked reduction in blood pressure in patient 1. Patient 2, not an operative candidate, responded satisfactorily to use of a converting enzyme inhibitor, which helped to confirm the dependency of the blood pressure on the abnormal flow relationship existing within that aberrant artery and the kidney. We believe these 2 patients are representative of a small but distinct subgroup within the larger number of patients with elongated single or multiple renal aberrant arteries. Each aberrant artery had no focal stenosis, although a decrease in flow relative to the tissue perfusion demands was apparent from the marked activation of the renin-angiotensin system in the venous system draining that artery. The increased length of such vessels may contribute to their decreased flow, although their average diameter may reside just above such a critical value for a normal length vessel. This new syndrome, involving more than one component of the flow/resistance relationship, has been overlooked when renin-dependent forms of hypertension are considered.

Urological manifestations of vascular disease

We have detailed several of the urological manifestations of vascular disease. With the aging of the North American population, urologists will encounter the urological complications of vascular disease with ever-increasing frequency.

A comparison of outcome criteria in the diagnosis of renovascular hypertension

The outcome criteria used for the diagnosis of renovascular hypertension (RVHT) following renal revascularization have not been validated. Differing criteria of indeterminate accuracy have yielded conflicting conclusions concerning the prevalence and efficacy of treatment of RVHT. We compared the accuracy of conventional outcome criteria used in the diagnosis of RVHT to that of novel, ordered outcome analysis to determine whether such an analysis might provide a more consistent means of diagnosing RVHT. Twenty-seven patients underwent intervention for treatment of presumed RVHT (group I), and 40 patients with presumed essential hypertension were treated with antihypertensive medication alone (group II). A standard dichotomized (improved or unimproved) outcome scheme and a five-level, ordered outcome scheme (ranging from definitely unimproved to definitely improved) were used to generate nominal outcomes of therapy for each patient. The resultant outcome groups were examined to determine the effect of such partitioning on blood pressure and medication requirements. To determine their diagnostic accuracy, the conventional and ordered outcome schemes were compared with a consensus outcome scheme derived from the use of numerous criteria. Significant correlations were observed between the ordered outcome score and posttreatment reductions in systolic blood pressure (r = 0.53, p = 0.007), diastolic blood pressure (r = 0.74, p = 0.0001), and medication score (r = 0.71, p = 0.0001). Overall diagnostic accuracy was estimated to be 91% for ordered criteria and 85% for dichotomized criteria. Correlation of the ordered and conventional schemes' assignments with the consensus scheme's assignments was 0.79 (p = 0.0001) and 0.63 (p = 0.0001), respectively. A simple, ordered outcome scheme compares favorably with the standard dichotomized scheme in assigning a diagnosis of RVHT to patients following renal revascularization or nephrectomy. The ordered scheme offers the advantages of simplicity and accuracy over current schemes.

Secondary hypertension: evaluation and treatment

Most patients with hypertension in the United States have essential (primary) hypertension (95%), the cause of which is unknown. The remaining 5% of adults with hypertension have the secondary form of hypertension, the cause and pathophysiologic process of which are known. Internists and other primary care physicians refer to this as treatable or curable hypertension, because the hypertension can be managed or even controlled with medications. Similarly, the condition is called surgical hypertension by surgeons in the belief that once the cause is determined and identified, surgical intervention will result in cure of hypertension. Secondary causes of hypertension include renal parenchymal disease, renovascular diseases, coarctation of the aorta, Cushing's syndrome, primary hyperaldosteronism, pheochromocytoma, hyperthyroidism, and hyperparathyroidism. Occasionally included in this category are alcohol- and oral contraceptive-induced hypertension and hypothyroidism, but these conditions are not discussed herein. The evaluation of secondary hypertension is of interest and can bring together different facets of anatomy, physiology, pharmacology, and radiology in the medical and surgical treatment of these disorders. Despite enthusiasm that can be generated in the evaluation of these conditions, evaluation can be expensive and should not be conducted for all patients with hypertension. Features that aid in the diagnosis of secondary hypertension include the following: 1. Onset of hypertension before the age of 20 or after the age of 50 years. The presence of hypertension at a young age may suggest coarctation of the aorta, fibromuscular dysplasia, or an endocrine disorder. Hypertension found for the first time after the age of 50 years may suggest the presence of renovascular hypertension caused by atherosclerosis. 2. Markedly elevated blood pressure or hypertension with severe end-organ damage, as in grade III or IV retinopathy. These findings suggest the presence of renovascular hypertension or pheochromocytoma. 3. Specific body habitus and ancillary physical findings. For example, truncal obesity and purple striae occur with hypercortisolism, and exophthalmos is associated with hyperthyroidism. 4. Resistant or refractory hypertension (poor response to medical therapy usually necessitating use of more than three antihypertensive medications from three different classes). 5. Specific biochemical test that suggest the existence of certain disorders, such as hypercalcemia in hyperparathyroidism, hyperglycemia in Cushing's syndrome and pheochromocytoma, and unprovoked hypokalemia with renin-producing tumors, primary hyperaldosteronism, or renin-mediated renovascular hypertension. 6. Other characteristics that may suggest secondary hypertension such as abdominal diastolic bruits (renovascular hypertension), decreased femoral pulses (coarctation of the aorta), or bitemporal hemianopias (Cushing's disease). A combination of a good history and physical examination, astute observation, and accurate interpretation of available data usually are helpful in the diagnosis of a specific causation.

Acute blockage of the renin system and differential renal vein renin determinations in the diagnosis of renovascular hypertension

For validation of differential renal vein renin determinations in the diagnosis of renovascular hypertension (RVH), we investigated 102 patients suspected of suffering from RVH before and 1 h after administration of 25 mg captopril. Sensitivity, specificity and posterior probability for renin ratio (RR) and renin secretion (RS) were calculated based on 44 patients with proven RVH and 58 patients with primary hypertension (PH) using discriminant analysis. There is good (> 95%) and identical specificity of both variables under all conditions, whereas sensitivity remains poor even after Captopril administration (RR 23% vs. 32%; RS 20% vs. 34%). The posterior probabilities obtained by discriminant analysis revealed a cut-off point of 2.5 for the renin ratio and of 1.9 for the renin secretion. No change is observed after ACE inhibition. We conclude that the acute blockade of the renin system by captopril in differential renin sampling yields no advantages in diagnosing RVH and that there is no difference between RR and RS in the diagnosis of RVH.

Noninvasive diagnosis of renovascular disease

OBJECTIVE

To present the epidemiologic and clinical features of renovascular disease and discuss various diagnostic approaches.

DESIGN

We describe the findings in patients with fibromuscular dysplasia or atherosclerotic disease of the renal arteries and review pertinent studies from the literature.

RESULTS

Renovascular disease is an important cause of resistant hypertension and progressive renal insufficiency, particularly in the elderly population. Improved blood pressure control and renal function after revascularization have generated intense interest in identifying those patients likely to benefit from this intervention. Fibromuscular dysplasia and atherosclerotic renal artery stenosis account for most cases of renovascular disease. Both entities produce resistant hypertension; the latter is the more common cause of progressive renal insufficiency--occasionally leading to end-stage renal disease. Angiotensin-converting enzyme inhibitor-related renal dysfunction, otherwise unexplained renal insufficiency, and recurrent pulmonary edema are increasingly recognized clinical manifestations of renovascular disease. Traditional screening tests such as intravenous pyelography, intravenous digital subtraction angiography, radionuclide scintirenography, and measurement of the peripheral venous plasma renin activity have limited accuracy for diagnosing renal artery stenosis and do not accurately predict the blood pressure response to revascularization. In comparison, recently developed noninvasive tests such as captopril renography, renal artery duplex sonography, and magnetic resonance angiography seem to be more accurate and, in the case of captopril renography, may be more predictive of the blood pressure response to revascularization.

CONCLUSION

Future directions in the area of renovascular disease should include a direct comparison among these new noninvasive diagnostic techniques, with a particular focus on the identification of those patients most likely to benefit from revascularization in terms of both blood pressure control and improved renal function.

Defining the role of renal angiography in the diagnosis of renal artery disease

The current goal of angiography in the diagnosis of renal artery disease is poorly defined, probably because of the diversity of patients presenting for management. The current application of angiography is better understood when put into perspective with the patient population that we are trying to screen. There are two distinct patient populations with renovascular disease: those with uncontrolled hypertension and those with azotemia or risk of progression to end-stage renal disease. The role of angiography in these two patient populations is quite different. In patients with hypertensive renovascular disease, angiography should be applied rather late and should be preceded by other noninvasive testing to screen patients from those with essential hypertension, since the prevalence of this disease is low and the cost implications of applying angiography primarily are immense. The two promising tests in this setting are captropril renography and duplex ultrasound scanning. In contradistinction, patients with azotemic renovascular disease, suffering from bilateral renal artery stenoses, or suffering from stenosis of the renal artery in a solitary kidney may be better studied by early application of renal angiography, especially those at risk of progression and for whom intervention is indicated.

Secondary hypertension: workup and correction

The three most common causes--renal artery stenosis, pheochromocytoma, and primary aldosteronism--are reviewed, including uncomplicated screening procedures to select candidates for a more intensive workup. The first two conditions are usually corrected by angioplasty or surgery, whereas aldosteronism may require both surgical and medical therapy or medication alone.

Simultaneous reconstruction of infrarenal abdominal aorta and renal arteries

From 1980 to 1990, 48 (4.7%) of 1,002 patients underwent elective aortic reconstruction and simultaneous renal artery reconstruction. Forty-five men and three women (mean age: 66.5 years) had 59 renal artery lesions (51 stenoses, six occlusions, one dysplasia, and one aneurysm) associated with 20 infrarenal aortic aneurysms and 28 aortoiliac occlusive lesions. One nephrectomy and 58 renal artery reconstructions were performed (35 prosthetic bypasses, 11 vein bypasses, six direct reimplantations, five transaortic endarterectomies, and one resection of an intrahilar aneurysm followed by autotransplantation). Operation was always indicated for the aortic lesions. Indication for renal artery repair was hypertension in 33 cases (17 associated with renal insufficiency) and one with isolated renal insufficiency. In the remaining 14 cases, surgery was deemed preventive. One patient died (2%). There were 12 nonfatal complications two of which were kidney failures requiring chronic extrarenal epuration. Routine follow-up arteriograms showed four postoperative renal artery occlusions. Mean follow-up was 35.8 months. Four patients were lost to follow-up; 10 died secondarily. Five year survival was 72.1 +/- 19.1%. Secondary patency of renal artery reconstruction was 89.5 +/- 9.4% at five years. Late results were favorable in 45% of patients with hypertension and in 39% of patients with renal insufficiency. Mortality in simultaneous aortic and renal artery reconstruction is not superior to that of isolated infrarenal aortic surgery.

Encephalopathy in renovascular hypertension associated with the use of oral contraceptives

Two female patients aged 19 years and 27 years presented with hypertensive encephalopathy and were subsequently found to have renal artery stenosis due to fibromuscular dysplasia. Both patients had had normal blood pressures recorded within the previous 6 months whilst taking the oral contraceptive pill. Their neurological state returned to normal with hypertensive control and in one case the hypertension was cured by dilatation of the renal artery stenosis by balloon angioplasty.

Detection and investigation of renal artery stenosis

A retrospective analysis was done on 235 hypertensive patients undergoing renal arteriography. Of the 85 patients with renal artery stenosis 50 underwent 56 operations or angioplasties and have been followed up for at least a year. 41 (73%) of these procedures were curative or led to improved blood-pressure control. These results make it worthwhile identifying hypertensive patients with renal artery stenosis who may benefit from surgery or angioplasty. Vascular disease, epigastric bruit, and impaired renal function were commoner in the renal artery stenosis patients than in the 81 with normal arteriograms, but there were no features pathognomonic of stenosis. Intravenous urography had a sensitivity of 83% and a specificity of 69.5% in identifying renal artery stenosis; those for isotope renography were 90.5% and 38.5%, respectively. Divided renal vein renins did not predict the outcome of intervention. Arteriography should, if there are no contraindications to intervention, be the first and definitive investigation when renal artery stenosis is suspected--for instance, in hypertensive patients with accelerated or malignant hypertension, those whose blood pressure is poorly controlled by multiple therapy, and those who have had recent deterioration in blood-pressure control or renal function.

Indication for intervention in patients with renovascular hypertension

It is now possible to accurately identify patients with renovascular hypertension who need renal angioplasty or revascularization. Evaluation does not require hospitalization and begins with the determination of an ambulatory plasma renin activity (PRA) indexed against sodium excretion and a captopril test. Subsequently differential renal vein renins with matching inferior vena caval (IVC) renins are measured often with converting enzyme inhibition. Identifying criteria are as follows: (1) high PRA indexed against sodium excretion, (2) hypersecretion of renin following captopril administration, (3) absence of renin secretion from the contralateral kidney, and (4) an ipsilateral renal vein renin increment at least 50% greater than the matching IVC renin. Patients who meet the criteria are admitted for percutaneous transluminal renal angioplasty.