Module 11.3 - Renal Artery Stenosis

Question 1

What is renal artery stenosis?

Answer 1

Renal artery stenosis (RAS) is a stenosis (or narrowing) in the lumen of the main renal artery or in its proximal branches. It can be the cause of primary, or secondary, hypertension.

Question 2

What are the 2 main causes of renal artery stenosis?

Answer 2

1. Atherosclerosis – (accounts for 90% of cases) affects patients > 45 years of age; usually involving the proximal main renal artery
2. Fibromuscular dysplasia (FMD) – (accounts for < 10% of cases) affects women under age of 50 years; due to an abnormality in the muscular lining of the renal artery; typically involves distal main renal artery or intrarenal branches; familial tendency

Question 3

Describe the pathophysiology associated with renal artery stenosis

Answer 3

A. Reduced blood flow to kidney due to atherosclerotic renal artery causes the kidney to release increased renin, which results in hypertension.

B. Renal vascular hypertension can be severe, or refractory, and difficult to control.

C. RAS causes the kidney to have decreased arterial blood flow, so it atrophies over time, termed ‘ischemic nephropathy’.

D. Hypertensive nephrosclerosis can develop.

E. Persistently elevated blood pressure in the non-stenotic kidney can cause progressive sclerosis (scarring) and decrease in renal function.

F. Unilateral RAS and bilateral RAS can lead to chronic kidney disease

Question 4

What are the signs and symptoms associated with renal artery stenosis?

Answer 4

Usually asymptomatic until stenosis is severe and hypertension is severe to refractory.

RAS should be considered in the following cases:

• Onset of HTN at < 30 years of age or > 55 years of age
• HTN was well controlled and now difficult to treat (requiring 3 or more BP meds)
• Malignant, accelerated or resistant HTN
• No family history of HTN
• Unexplained heart failure or flash pulmonary edema
• Asymmetric kidneys on ultrasound
• Epigastric or renal artery bruits (on auscultation or ultrasound)
• Atherosclerotic disease of aorta or peripheral arteries (diffuse disease)
• A decline in estimated GFR > 30% from baseline renal function AFTER initiation of ACE-I or ARB
• Metabolic acidosis

Question 5

What lab/diagnostic tests are done to diagnose renal artery stenosis?

Answer 5

• Doppler Ultrasound – useful for diagnostic screening only
• CT angiography of renal arteries – requires IV contrast administration with increased risk of contrast induced nephropathy; only performed Magnetic Resonance Arteriography (MRA) is contraindicated.
• MRA – provides functional assessment of renal blood flow; no radiation required; uses gadolinium based contrast- must be avoided in patients with moderate to end stage renal failure
• Renal angiography – invasive; Gold standard of diagnosis; the most direct measure of hemodynamic and functional significance of stenosis; treatment can be performed at same time, such as percutaneous transluminal angioplasty (PTA) and/or stent placement; there is still a risk of contrast-induced nephropathy present.
• Renal vein renin sampling, peripheral renin levels and captopril renal scintigraphy is not recommended due to low specificity and sensitivity.

Question 6

How do you manage a patient with renal artery stenosis?

Answer 6

A. Lifestyle changes to control HTN: exercise, health weight, healthy diet, smoking cessation

B. Medical management:

• Optimize glycemic control, blood pressure and cholesterol management

Medications:

• 1st line: ACE – I and ARBs have been shown to slow the progression of kidney disease. Use with caution in RAS- can cause further decline in GFR due to angiotensin inhibition; check renal function within 2 weeks of initiation
• 2nd line - Thiazide diuretic
• 3rd line - Calcium channel blocker
• 4th line - Mineralocorticoid receptor antagonist
• Other - Beta-blocker

All patients with RAS should be screened for coronary artery disease, hyperlipidemia and peripheral vascular disease