Renovascular Hypertension

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 1 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.

The vast majority of patients with hypertension have primary hypertension. That is, there is no underlying medical reason for hypertension—they just have high blood pressure. Approximately 10% of patients have secondary hypertension, with an underlying reason, which, if identified and treated, would cure or lower the high blood pressure. The most common causes of secondary hypertension include chronic kidney disease and 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)).

One important secondary cause of hypertension, which has good results from treatment, is renal artery stenosis (RAS). Stenosis means narrowing, or partial blockage of the blood vessel that carries blood to the kidney. RAS may occur in younger (commonly female) patients, due to abnormal development of the artery wall known as fibromuscular dysplasia. The cause of renovascular hypertension in older patients is usually hardening of the arteries or atherosclerosis. Atherosclerosis is the most common cause of RAS. RAS is often found in patients with vascular disease in other areas (for example: coronary, carotid, abdominal aorta, peripheral arteries). In patients with atherosclerosis elsewhere, the likelihood of finding significant RAS is anywhere between 30-50%! RAS is associated with several serious medical conditions, including increasing high blood pressure (a serious predictor of heart attack, stroke, kidney failure, and premature death), kidney failure, and recurrent heart failure.

Atherosclerosis is a progressive disorder. If unrecognized and/or untreated, RAS is also progressive, and gets worse. Over the course of two years after identification of RAS, 11% of the arteries in one medical study went on to complete blockage!

RAS is associated with certain clinical clues, which if appreciated 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 >3 medications at maximal doses for blood pressure control
• Severe high blood pressure with a symptom (heart attack, stroke, aortic dissection—or rupture)
• Development of renal failure when taking certain medications
• Angiotensin Converting Enzyme Inhibitors (captopril, enalapril, lisinopril, etc)
• Angiotensin II Receptor Antagonists (losartan, candesartan, irbesartan, etc)
• High blood pressure and artery disease in the coronary, carotid, lower extremity arteries, or 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

Treatment of RAS generally falls into three categories:

• Medical Treatment
• Drug therapy of high blood pressure
• Antiplatelet therapy (for example: aspirin, clopidogrel)
• Cholesterol-lowering medications
• Tobacco cessation
• Control of blood sugar
• Follow-up of RAS to make sure that it is not getting worse
• Open Surgery
• Endarterectomy—the plaque, that causes renal artery stenosis is removed from the artery
• Renal bypass—the blocked artery is replaced by a new artery using a vein from the leg or using a synthetic artery
• Endovascular Therapy
• Balloon Angioplasty (PTRA: percutaneous transluminal renal angioplasty)—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. This technique is usually used in patients with hardening of the arteries.

The decision regarding which option is best 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. Whether fixing RAS prevents progression to kidney failure is uncertain, and major clinical trials will begin shortly with the hope of answering this important question.

About the author: Michael R. Jaff, DO, FACP, FACC, is the Director of the vascular diagnostic laboratory and vascular ultrasound core laboratory at Massachusetts General Hospital in Boston. He is president of the Society for Vascular Medicine and Biology, and is a noted national speaker.