Treatment options for renovascular hypertension

Management of asymptomatic carotid stenosis

Patients with asymptomatic carotid stenosis (ACS) are at very high risk of coronary events, so they should all receive intensive medical therapy. What is often accepted as “best medical therapy” is usually suboptimal. Truly intensive medical therapy includes lifestyle modification, particularly smoking cessation and a Mediterranean diet. All patients with ACS should receive intensive lipid-lowering therapy, should have their blood pressure well controlled, and should receive B vitamins for lowering of plasma total homocysteine (tHcy) if levels are high; a commonly missed cause of elevated tHcy is metabolic B12 deficiency, which should be diagnosed and treated. Most patients with ACS would be better treated with intensive medical therapy than with either carotid endarterectomy (CEA) or stenting (CAS). A process called “treating arteries instead of treating risk factors” markedly reduced the risk of ACS in an observational study; a randomized trial vs. usual care should be carried out. The few patients with ACS who could benefit (~15%, or perhaps more if recent evidence regarding the risk of intraplaque hemorrhage is borne out) can be identified by a number of features. These include microemboli on transcranial Doppler, intraplaque hemorrhage, reduced cerebrovascular reserve, and echolucency of plaques, particularly “juxtaluminal black plaque”. No patient should be subjected to CAS or CEA without evidence of high-risk features, because in most cases the 1-year risk of stroke or death with intervention is higher with either CEA (~2%) or CAS (~4%) than with intensive medical therapy (~0.5%). Most patients, particularly the elderly, would be better treated with CEA than CAS. Most strokes can be prevented in patients with ACS, but truly intensive medical therapy is required.

The need for clinical judgement in the application of evidence-based medicine

BACKGROUND

Evidence-based medicine (EBM) has no doubt resulted in great improvements in the practice of medicine. However, there are problems with overly zealous application of EBM, that for some amounts to religious practice. When good evidence exists, it should guide therapeutic and diagnostic choices. However, when evidence is lacking for a given patient, medicine is best practised by extrapolation from available evidence, interpreted in the light of the pathophysiology of the condition under consideration, and effects of various therapies in relation to that pathophysiology.

OBJECTIVE

To assess ways in which the unthinking application of EBM can go wrong; these include withholding therapy in patients whose subgroup was excluded from clinical trials, blind acceptance of the numbers, reliance on studies with crucial design flaws and reliance on intention-to-treat analysis when it is not appropriate.

STUDY SELECTION

Examples assessed included withholding cholesterol-lowering therapy in the elderly, not using B-vitamin therapy for stroke prevention, not using revascularisation for true renovascular hypertension and avoiding statin therapy for fear of intracerebral haemorrhage.

FINDINGS

Zealous application of EBM is often inappropriate.

CONCLUSIONS

In some instances, when there is a lack of evidence, or faulty interpretation of the evidence, clinical judgement should inform the application of EBM.

Treatment of severe hypertension in a 14-year-old child: Successful blood pressure control with additive administration of captopril, an angiotensin-converting enzyme inhibitor, in a patient with bilateral renovascular hypertension

We report a 14-year-old boy with recurrent episodes of headache caused by uncontrolled hypertension. The diagnosis of renovascular hypertension due to Takaysu arteritis (TA) was made based on an increase in erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) and computed tomography (CT) image of bilateral renal artery stenosis was taken. Renal scintigraphy revealed normal perfusion and function of the right kidney and severe reduction of the perfusion and function of the left kidney. Careful drug adjustments significantly improved but did not fully control the blood pressure (BP); further, angioplasty, which showed almost occlusion of the left renal artery opening and the minor narrowing of the right renal artery, failed to regain sufficient BP control. The addition of captopril, an angiotensin-converting enzyme (ACE) inhibitor, to conventional antihypertensive drugs successfully and safely lowered BP and preserved the renal function. This unique case suggested that ACE inhibitors achieved better control of BP in a patient with bilateral renal stenosis and that the patient may have hemodynamically significant stenosis caused by unilateral renal artery.

Losartan reduces oxidative stress within the rostral ventrolateral medulla of rats with renovascular hypertension

BACKGROUND

Previous studies showed that the microinjection of antioxidants or the overexpression of superoxide dismutase within the rostral ventrolateral medulla (RVLM) reduces hypertension and sympathoexcitation in the 2-kidney, 1-clip (2K-1C) model. In this study, we hypothesized that angiotensin II (ANG II) type 1 receptor (AT1R) is involved in the oxidative stress within the RVLM and contributes to cardiovascular dysfunction in renovascular hypertension.

METHODS

Losartan (30mg/kg/day, oral gavage) was administered for 7 consecutive days by week 5 after implantation of the clip (gap width = 0.2mm). Mean arterial pressure, baroreflex, and renal sympathetic nerve activity (rSNA) were evaluated. Superoxide production was evaluated by dihydroethidium (DHE) staining within the RVLM and within a control area. Systemic oxidative stress was characterized by measurement of thiobarbituric acid reactive substances (TBARS) and total glutathione (tGSH) in the blood.

RESULTS

AT1R blockade significantly (P < 0.05) reduced hypertension by approximately 20% (n = 11) and sympathoexcitation to the kidneys by approximately 41% (n = 6) in the 2K-1C rats. Losartan treatment increased the baroreflex sensitivity of rSNA to pressor (67%) and depressor (140%) stimuli in the 2K-1C rats. AT1R blockade caused a significant (66%) reduction in DHE staining within the RVLM but not within the control area, reduced plasma TBARS (from 1.6±0.1 to 1.0±0.1 nmol/ml), and increased tGSH (from 3.4±0.4 to 5.2±0.3 μmol/g Hb) in the 2K-1C group only.

CONCLUSIONS

Our findings suggest that the beneficial effects of ANG II blockade in renovascular hypertension are partly due to preferential reduction of oxidative stress in the RVLM.

Physiologic tailoring of treatment in resistant hypertension

Resistant hypertension is a major opportunity for prevention of cardiovascular disease. Despite widespread dissemination of consensus guidelines, most patients are uncontrolled with approaches that assume that all patients are the same.

Causes of resistant hypertension include 1) non-compliance 2) consumption of substances that aggravate hypertension (such as salt, alcohol, nonsteroidal anti-inflammatory drugs, licorice, decongestants) and 3) secondary hypertension.

Selecting the appropriate therapy for a patient depends on finding the cause of the hypertension. Once rare causes have been eliminated (such as pheochromocytoma, licorice, adult coarctation of the aorta), the cause will usually be found by intelligent interpretation (in the light of medications then being taken) of plasma renin and aldosterone.

If stimulated renin is low and the aldosterone is high, the problem is primary aldosteronism, and the best treatment is usually aldosterone antagonists (spironolactone or eplerenone; high-dose amiloride for men where eplerenone is not available). If the renin is high, with secondary hyperaldosteronism, the best treatment is angiotensin receptor blockers or aliskiren. If the renin and aldosterone are both low the problem is over-activity of renal sodium channels and the treatment is amiloride. This approach is particularly important in patients of African origin, who are more likely to have low-renin hypertension.

Etiopathology of chronic tubular, glomerular and renovascular nephropathies: clinical implications

Chronic kidney disease (CKD) comprises a group of pathologies in which the renal excretory function is chronically compromised. Most, but not all, forms of CKD are progressive and irreversible, pathological syndromes that start silently (i.e. no functional alterations are evident), continue through renal dysfunction and ends up in renal failure. At this point, kidney transplant or dialysis (renal replacement therapy, RRT) becomes necessary to prevent death derived from the inability of the kidneys to cleanse the blood and achieve hydroelectrolytic balance. Worldwide, nearly 1.5 million people need RRT, and the incidence of CKD has increased significantly over the last decades. Diabetes and hypertension are among the leading causes of end stage renal disease, although autoimmunity, renal atherosclerosis, certain infections, drugs and toxins, obstruction of the urinary tract, genetic alterations, and other insults may initiate the disease by damaging the glomerular, tubular, vascular or interstitial compartments of the kidneys. In all cases, CKD eventually compromises all these structures and gives rise to a similar phenotype regardless of etiology. This review describes with an integrative approach the pathophysiological process of tubulointerstitial, glomerular and renovascular diseases, and makes emphasis on the key cellular and molecular events involved. It further analyses the key mechanisms leading to a merging phenotype and pathophysiological scenario as etiologically distinct diseases progress. Finally clinical implications and future experimental and therapeutic perspectives are discussed.

Effects of chronic sympatho-inhibition on reflex control of renal blood flow and plasma renin activity in renovascular hypertension

BACKGROUND AND PURPOSE

We determined if chronic sympatho-inhibition with rilmenidine has functional significance for the kidney by altering responses of renal blood flow (RBF) and plasma renin activity (PRA) to stress and acute hypotension in rabbits with renovascular hypertension.

EXPERIMENTAL APPROACH

RBF to each kidney and renal sympathetic nerve activity (RSNA) to the left kidney were measured in rabbits in which a renal artery clip induced hypertension (2K1C) and in sham-operated rabbits. After 2 weeks, a subcutaneous minipump was implanted to deliver rilmenidine (2.5 mg.kg(-1).day(-1)) to 2K1C rabbits for 3 weeks.

KEY RESULTS

After 5 weeks of renal artery stenosis, mean arterial pressure (MAP) was 23% higher and PRA 3-fold greater than in sham-operated rabbits. Blood flow and renal vascular conductance in the stenosed kidney were lower (-75% and -80%) compared with sham, and higher in the non-clipped kidney (68% and 39%). Responses of RBF and PRA to hypotension were similar in 2K1C and sham rabbits. Airjet stress evoked a greater increase in MAP in 2K1C rabbits than sham controls. Chronic rilmenidine normalized MAP, reduced RSNA and PRA, and did not reduce RBF in the stenosed kidney. Responses of RBF (clipped and non-clipped kidney), RSNA and PRA to hypotension and airjet were little affected by rilmenidine.

CONCLUSIONS AND IMPLICATIONS

Our observations suggest that chronic sympatho-inhibition is an effective antihypertensive therapy in renovascular hypertension. It normalizes MAP and reduces basal PRA without compromising blood flow in the stenosed kidney or altering responses of MAP, haemodynamics and PRA to acute hypotension and stress.

Angiotensin inhibition in renovascular disease: a population-based cohort study

BACKGROUND

Angiotensin-converting enzyme inhibitors and angiotensin receptor blockers effectively reduce blood pressure in patients with renovascular disease (RVD); yet, randomized cardiovascular prevention trials of these drugs typically exclude individuals with this condition.

PATIENTS AND METHODS

We studied the association of renin-angiotensin system inhibition with prognosis in a population-based cohort comprising 3,570 patients with RVD in Ontario, Canada; slightly more than half (n = 1,857, 53%) were prescribed angiotensin inhibitors. The primary outcome was the composite of death, myocardial infarction, or stroke. Secondary outcomes included individual cardiovascular and renal events.

RESULTS

Patients receiving angiotensin inhibitors had a significantly lower risk for the primary outcome during follow-up (10.0 vs 13.0 events per 100 patient-years at risk, multivariable adjusted hazard ratio [HR] 0.70, 95% CI 0.59-0.82). In addition, hospitalization for congestive heart failure (HR 0.69, 95% CI 0.53-0.90), chronic dialysis initiation (HR 0.62, 95% CI 0.42-0.92), and mortality (HR 0.56, 95% CI 0.47-0.68) was lower in treated patients. Conversely, patients receiving angiotensin inhibitors were significantly more likely to be hospitalized for acute renal failure during follow-up (HR 1.87, 95% CI 1.05-3.33; 1.2 vs 0.6 events per 100 patient-years at risk).

CONCLUSIONS

These data emphasize the high vascular risk of RVD and suggest that angiotensin inhibitors may improve prognosis in this setting at the expense of acute renal toxicity. If the latter are selected in the management of RVD, renal function parameters should be assiduously followed.

Stroke prevention in the high-risk patient

Strokes are increasing in number due to an ageing population and are largely preventable. In the highest risk patients, a 90% relative risk reduction for stroke is attainable by appropriately using all the measures proven to reduce stroke: smoking cessation, a Mediterranean diet, control of hypertension, anticoagulants or antiplatelet agents, lipid lowering drugs and appropriate carotid endarterectomy. Vitamin therapy to lower homocysteine and carotid stenting are additional measures that may yet prove beneficial. Diet, smoking cessation and appropriate carotid endarterectomy reduce stroke by more than do pharmacotherapies. Blood pressure control depends more on selecting appropriate therapy individualised for the patient, than on using any particular drug class. This review, therefore, places pharmacotherapy in perspective as part of, but not all of, stroke prevention.