Visceral Artery Imaging/Hemodialysis Access Evaluation

Question 1

how to tell if mesenteric ischemia is acute or chronic

Answer 1

patients with acute mesenteric ischemia, often from an embolus, will present with severe abdominal pain - possible medical emergency due to. possibility of intestinal necrosis

Question 2

describe normal celiac artery velocity, >70% stenosis and occlusion

Answer 2

normal <200 cm/sec

> 70% = >200 cm/sec with post stenotic turbulence

occlusion = no detectable signal, retrograde common hepatic artery flow

Question 3

describe normal SMA velocity, >70% stenosis and occlusion

Answer 3

normal <275 cm/sec

> 70% = >275 cm/sec with post stenotic turbulence

occlusion = no detectable signal, often reconstitutes distally via collaterals

Question 4

describe normal IMA velocity, >70% stenosis and occlusion

Answer 4

normal/>70% stenosis = no established criteria

occlusion = no detectable signal

Question 5

if celiac and SMA are normal, isolated IMA stenosis is:

Answer 5

unlikely to be symptomatic

often small - if noted to be large, may suggest collateralization

Question 6

what are two possible connections between SMA and IMA

Answer 6

marginal artery of the colon (aka marginal artery of Drummond)

arc of riolan

Question 7

IMA may also serve as collateral to the iliac arteries via

Answer 7

branches of the internal iliac artery

Question 8

what changes after eating? Celiac artery or SMA

Answer 8

SMA

pre prandial - high resistance flow pattern, flow reversal often present
post prandial - converts to Low resistance

Question 9

median arcuate ligament syndrome (MALS)

(also known asa arcuate ligament compression syndrome or celiac axis compression syndrome)

Answer 9

compression of the celiac artery origin by the median acute ligament of the diaphragm

stenosis may occur during normal breathing or expiration as the arcuate ligament compresses the celiac artery

Question 10

what are the clinical signs of MALS

Answer 10

abdominal bruit which disappears with deep inspiration

on expiration - the median arcuate ligament compresses the ventral aspect of the celiac artery creating an “S” shaped vessel course and a stenosis

with deep inspiration - the ligament releases the artery, it straightens, and the stenosis resolves with PS <200 cm/s

Question 11

what is the difference between essential hypertension and secondary hypertension

Answer 11

essential hypertension - no direct identifable cause

secondary hypertension - hypertension that is the result of some other disease, commonly of the kidney

Question 12

renovascular hypertension

Answer 12

caused by renal artery stenosis. the release of renin, promoting conversion of angiotensinogen to angiotensin causing vasoconstriction and subsequent high blood pressure

this eventually results in renal failure

Question 13

what is the landmark for identifying the renal arteries

Answer 13

the left renal vein as it crosses over the aorta just below the origin of the SMA

Question 14

what is the normal PSV for kidneys

Answer 14

<180cm/sec

Question 15

what is considered 60% or greater stenosis for kidneys

Answer 15

> 180-200 cm/sec

Question 16

what is the renal aortic ratio formula and what is considered normal/abnormal

Answer 16

RAR = highest renal artery PSV / aorta PSV

normal <3.5
abnormal >3.5

** do not use if AAA is present or if aorta PSV is <40 or >90 cm/s

Question 17

what is the formula for resistivity index (RI), what is considered normal/abnormal

Answer 17

RI = PSV-EDV/PSV

normal <0.8
abnormal >0.8

Question 18

what is the formula for end diastolic ratio, what is considered normal/abnormal

Answer 18

EDR = EDV/PSV

normal >0.2
abnormal <0.2

Question 19

what is considered normal/abnormal for acceleration time

Answer 19

normal <100 milliseconds
abnormal >100 milliseconds

Question 20

how to tell the difference between atherosclerotic stenosis of the kidney vs fibromuscular dysplasia

Answer 20

stenosis at the original of the renal artery is atherosclerotic

lesion in the mid or distal artery segment is typical of fibromuscular dysplasia, FMD is more likely in young/middle aged females

Question 21

what is dialysis

Answer 21

treatment for renal failure

filtering blood externally

Question 22

types of dialysis access

Answer 22

synthetic grafts - typically PTFE (gortex) - synthetic material used to connect an artery to a vein, may be straight or looped

native autogenous fistula - a vein is connected directly to the artery. this fistula will “mature” and the vein dilates in response to the arterial pressure
breccia-cimino fistula - describes a radial artery to cephalic vein fistula

Question 23

T or F: a bruit or thrill is considered normal in dialysis access

Answer 23

true

Question 24

where is the most common sites of stenosis in dialysis patients

Answer 24

venous anastomosis and outflow vein

Question 25

what is considered a normal waveform for dialysis access

Answer 25

high velocity, low resistance waveform

abnormal: high resistance, abnormal outflow; decreased systolic upstroke, dampened waveform, low velocities, ? inflow disease

Question 26

what is the general velocity criteria for >50% stenosis in relation to dialysis access

Answer 26

at the anastomosis: PSV >400 cm/s, velocity ratio >3, intraluminal defect

along the venous outflow: PSV >300 cm/s, velocity ratio >2, velocities <50 cm/s

Question 27

steal syndrome

Answer 27

arterial blood flow distal to the fistula is reversed flowing into the venous circulation may result in hand ischemia (pain, pallor, even ulceration)

blood flow down the radial artery travels into the fistula. the blood flow through the ulnar artery travels through the palmar arch and up the radial artery in a retrograde fashion into the Low resistance fistula. the fistula “steals” blood from the hand which may results in poor perfusion or even ischemia of the fingers or hand

Question 28

what is the preferred method to assess steal syndrome

Answer 28

PPG tracing on multiple digits; manually compress the fistula and observe for changes

no changes - no steal
changes - steal