Renovascular Hypertension

Question 0

2 main causes of renal artery stenosis?

Answer 0

atherosclerosis (almost always caused by smoking)

fibromuscular dysplasia

Question 1

What is renovascular disease? Is it always symptomatic?

Answer 1

Any occlusion of renal arteries. No, it’s not always symptomatic, nor does it always cause HTN.
(lots of people only learn they have it when they’re being evaluated as potential kidney donors)

Question 2

How does location of occlusive lesion vary between atherosclerotic and fibromuscular dysplasia causes of renal artery stenosis?

Answer 2

Atherosclerotic: lesion usually proximal to aorta.
Fibromuscular: lesions distal to aorta.

Question 3

Is renovascular diasease a common cause of HTN?
How do you know if renal artery stenosis is causing secondary HTN?
(important!)

Answer 3

No - only 1-3% of HTN in the U.S. is caused by renovascular disease.
You don’t know that renal artery stenosis is causing secondary HTN until you fix the stenosis and the HTN goes away!

Question 4

Important: What is a huge risk factor for atherosclerotic type renovascular disease?

Answer 4

Smoking.

Question 5

Important: Why should you look for atherosclerotic disease in other organs before you do anything about somebody’s atherosclerotic renovascular disease?

Answer 5

It’s likely there. If you drop somebody’s BP by revascularizing the renal artery, you might cause ischemia of affected organs (eg. brain).

Question 6

Why does renal artery stenosis increase BP? (you know this)

Answer 6

Renin

Question 7

3 things that control renin release?

Answer 7

Baroreceptors.
Sympathetic nerves.
Macula densa.

Question 8

What adrenergic receptor governs sympathetic-driven renin release?

Answer 8

Beta-1

Can antagonize this with beta-blockers.

Question 9

If renal artery disease is unilateral, how does the unaffected kidney respond? How does this affect the affected kidney?

Answer 9

Normal kidney sees high BP -> pressure natriuresis.

Na+ / volume loss further decreases perfusion of the affected kidney -> more renin release.

Question 10

On what main factor is the HTN of unilateral renal artery disease dependent? (important!)

Answer 10

Angiotensin II.
If you give an ACE inhibitor or ARB, you’ll drop the BP significantly.
(diuretics won’t help much, as this is a slightly hypovolemic HTN)

Question 11

How does bilateral renal artery stenosis differ from unilateral in terms of mechanism of HTN?

Answer 11

There’s no normal kidney to cause a pressure diuresis, so renin just causes volume just accumulate.
Increased volume -> increased perfusion of kidneys -> new steady state.

Question 12

On what factor is bilateral renal artery disease most dependent?
(important!)

Answer 12

Hypervolemia.

Giving an ACE inhibitor / ARB won’t lower BP much until the volume is brought down. Renin is low to normal!

Question 13

Why is hypervolemia in bilateral renal artery disease bad?

Answer 13

Most worrisome would be pulmonary edema.

Question 14

Why is medical treatment of HTN secondary to bilateral renal artery disease tricky?

Answer 14

If you give diuretic + ARB, you’ll drop the BP. But the kidneys were dependent on that higher BP for perfusion, so you can see a rapid drop in GFR.
(drop in GFR with anti-hypertensive treatment can be an indication for renal artery revascularization)

Question 15

Example of an iatrogenic cause of renal artery occlusion?

Answer 15

Aortic stent (for AAA) can occlude one or both renal arteries.

Question 16

It’s difficult to know when you should revascularize someone with renal artery disease.

Answer 16

it’s true

Question 17

What’s one common difficulty with knowing if revascularization of a renal artery is indicated?

Answer 17

Degree of stenosis is often overestimated with imaging.

Question 19

What is potentially a better way to assess the significance of someone’s renal artery stenosis than percent occlusion?

Answer 19

Kidney oxygenation with fancy MR stuff.

Question 20

How does kidney oxygenation / hypoxia correlate to what you’d see on histology of a biopsy?

Answer 20

More hypoxia -> more scarring, inflammation, badness.

Question 21

When looking at doppler ultrasound of kidney, is pulsatility in the vessels good or bad? How is this quantified?

Answer 21

Pulsatility is bad.

Pulsatility can be expressed as resistance index… high resistance index = more pulsatility.

Question 22

What’s the potential utility of calculating the resistance index in a patient with renal artery disease?

Answer 22

Low resistance index may predict improved kidney function revascularization.
Patients with high resistance index don’t have improved kidney function after revascularization.

Question 23

Hypothesis for why high resistance index predicts poor response to revascularization?

Answer 23

In these kidneys, inflammatory and fibrotic changes may already have permanently impaired kidney function (and also caused increased pulsatility).