Renal Artery Stenosis

Renal artery stenosis (RAS) is a common cause of high blood pressure that is difficult to control, and it may also be a cause of progressive loss of kidney function. Stenosis means narrowing, or partial blockage, of the blood vessels that carries blood to the kidney. The cause of renovascular hypertension in older patients is usually atherosclerosis (hardening of the arteries). Atherosclerosis is the most common cause of RAS. RAS may also occur in younger (commonly female) patients, due to abnormal development of the artery wall known as fibromuscular dysplasia (see article beginning on page 1 for information about FMD).

RAS is often found in patients with vascular disease in other areas, such as in the coronary, carotid, abdominal aortic and peripheral arteries. In patients with atherosclerosis elsewhere, the likelihood of finding significant RAS is between 30-50%! In approximately 15% of the cases, patients with coronary artery disease will have atherosclerotic narrowing in the renal arteries. RAS may be asymptomatic, but it can be associated with several serious medical conditions, including increased high blood pressure (a predictor of heart attack, stroke, kidney failure, and premature death), kidney failure, and congestive heart failure.

Hypertension (high blood pressure) represents the most common reason for health-care office visits in the United States. It is estimated that over 50 million Americans and over one billion people worldwide have hypertension. Recently, the seventh report of the Joint National Committee on the Prevention, Detection, Evaluation, and Treatment of Hypertension changed the definition of hypertension to >120/80 mmHg. This will increase the number of Americans who are candidates for aggressive risk-factor intervention and drug treatment for newly diagnosed hypertension. RAS is the most common cause of "correctable" hypertension and may be present in up to one million Americans.

The vast majority of patients with hypertension have primary hypertension—there is no underlying medical reason for hypertension—they just have high blood pressure. Approximately 10% of patients have secondary hypertension; that is, there is an underlying reason which, if identified and treated, would cure or lower high blood pressure. The most common causes of secondary hypertension include chronic kidney disease; obesity; medications, for example: non-steroidal anti-inflammatory drugs (ibuprofen, etc); sympathomimetics (decongestants, anti-histamines); oral contraceptives; anabolic steroids; illicit substances (cocaine); and over-the-counter dietary supplements (ephedra).

RAS is due to progressive atherosclerosis and may result in narrowing of the kidney artery(ies). RAS is associated with certain clinical clues which, if recognized by physicians, may result in earlier diagnosis. Some of these clues include:

• Worsening blood pressure control in someone whose blood pressure had previously been well-controlled
• The need for more than three medications at maximal doses for blood pressure control
• Severe high blood pressure with a symptom (heart attack, stroke, aortic dissection or rupture) or sign (abnormal sound heard with a stethoscope over the abdomen, changes on eye exams, swelling in the ankles, or evidence of an enlarged heart)
• Development of renal failure when taking certain medications
• High blood pressure and artery disease in the coronary, carotid, or lower-extremity arteries, associated with an abdominal aortic aneurysm
• Major difference in kidney size from one side to the other
• Repeated episodes of sudden severe heart failure, especially if the heart-squeezing function is normal
• Kidney failure without an obvious cause

There are several excellent non-invasive tests which are commonly used for the diagnosis of RAS, including ultrasound, nuclear imaging tests, magnetic resonance arteriography, and "spiral" computed tomography (CT) scanning. All have their advantages and disadvantages, yet all have high degrees of accuracy.

Treatment of RAS generally falls into three categories:

1. Medical treatment

• Drug therapy of high blood pressure
• Antiplatelet therapy (for example: aspirin, clopidogrel)
• Cholesterol-lowering medications
• Stop smoking
• Managing your blood sugar if you have diabetes
• Follow-up of RAS to make sure that it is not getting worse

2. Open surgery

• Endarterectomy—the plaque that causes renal artery stenosis is removed from the artery (rarely performed any more)
• Renal bypass—the blocked artery is replaced by a new artery, using a vein from the leg or a synthetic artery

3. Endovascular therapy

• Balloon angioplasty or percutaneous transluminal renal angioplasty (PTRA)—a catheter is inserted through the artery at the groin and a balloon is inflated to open up the blocked kidney artery. This technique is most effective in patients with fibromuscular dysplasia
• Stent—a metal screen (scaffold) is placed in the artery to prevent it from collapsing after PTRA. This technique is usually used in patients with hardening of the arteries.

The federal government, after evaluating published scientific literature in the field of RAS and treatment, has recently concluded that the data supporting invasive therapy are not strong enough to recommend it over optimizing contemporary medical treatment. The Cardiovascular Outcomes in Renal Artery Lesions—(CORAL) trial is a federally-funded study which will, when completed, represent the largest trial ever performed to evaluate the benefits of renal artery stents in patients with RAS and high blood pressure.

The decision regarding the best treatment option is made by consulting with vascular experts, who take into consideration the level of high blood pressure; the degree of kidney-function problems; the overall health of the patient; the risk of the chosen procedure; and the likelihood of improvement. One thing is certain: Patients with RAS are at increased risk for atherosclerosis-related events, such as heart attack, stroke, aortic aneurysms, and even death, and they should be closely followed to assess their risk of such complications.

About the Author: Michael R. Jaff, DO, FACP, FACC, is the Medical Director of the Vascular Center and the vascular ultrasound core laboratory at Massachusetts General Hospital in Boston. He is a past-president of the Society for Vascular Medicine, and is a noted national and international lecturer and educator.