Chapter 14: Ultrasound Assessment of Arterial Bypass Grafts Flashcards
a surgically created joining of two vessels that were formerly not connected
anastamosis
a connection between an artery and a vein that was created as a result of surgery or by other iatrogenic means
arteriovenous fistula
A channel that diverts blood flow from one artery to another, usually done to shunt from one artery to another
graft
An increase in blood flow. This can occur following exercise. It can also occur following restoration of blood flow following periods of ischemia.
hyperemia
The great saphenous vein is left in place in its normal anatomic position and used to create a diversionary channel for blood flow around an occluded artery
in situ bypass
focal increase in diameter either along the bypass or at an anastamosis; thrombus may or may not be present
aneurysms and pseudoaneurysms
swirling of color flow into the dilated portion; “yin-yang” appears may be present with color changing from red to blue as flow fills the dilation
aneurysms and pseudoaneurysms
low-velocity, turbulent, disturbed flow will be present in the dilated segment; bi-directional flow in neck
aneurysms and pseudoaneurysms
A patent venous tributary will be present off the bypass graft; this tributary may be seen to communicate into the deep venous system
arteriovenous fistula
Color filling will be seen within the fistula, extending to the deep venous system; aliasing likely to be present
arteriovenous fistula
flow may be slightly pulsatile to continuous within the fistula; antegrade diastolic flow will be evident in the bypass proximal to the fistula
arteriovenous fistula
linear object seen extending for several centimeters, parallel to bypass walls
dissection
turbulent flow; red to blue flow may be seen in either lumen
dissection
disturbed flow with increased resistance; flow may be bidirectional
dissection
small projection into the vessel lumen usually less than 1 cm, not associated with a valve
intimal flap
disturbed flow or aliasing may be present
Intimal flap and myointimal hyperplase
occurs within the bypass or along anastamotic areas; focal increase in vessel wall thickness that protrudes into the lumen
Myointimal hyperplasia
increased velocities, turbulence, or aliasing may be present
myointimal hyperplasia
intraluminal echoes of varying echogenicity examinations
thrombus
no flow or reduced color filling of bypass lumen
thrombus
absent Doppler signal or, if present, increased resistance
Thrombus
Hyperechoic structures seen protruding into bypass lumen; may be partial or complete leaflet
valve remnants
may demonstrate disturbed color-flow patterns or aliasing in region of valves
valve remnants
may demonstrate elevated velocities in region of valve
valve remnants
made of various manufactured materials such as polytetraflurethylene (PTFE) or Dacron (woven composites)
prosthetic (synthetic) bypass grafts
preferred bypass graft material
autogeneous vein
Veins used for bypass grafts
great saphenous vein
small saphenous vein
cephalic veins
basilic veins
Better long-term patency
less thrombogenic
potential for early failure
autogenous vein bypass graft
low potential for early technical failure and ultrasound-detected abnormalities; worse long term success rate because of progressive stenoses
PTFE grafts
free vein graft where the vein is completely dissected free from natural position
orthograde bypass graft
Free vein graft that can be placed in a reversed position
retrograde bypass graft
proximal anastamosis of inflow arteries
common femoral
superficial femoral
popliteal
profunda femoral
distal anastamosis of outflow arteries
popliteal
tibioperoneal trunk
anterior tibial
posterior tibial
peroneal
Technical problems following a bypass graft procedure in the first 30 days.
retained valve or partial valve leaflet
intimal flap
problems at anastamotic sites
possible graft entrapment
bypass may thrombose
Bypass graft failure between months 1 and 24
Myointimal hyperplasia
after 24 months following a bypass graft procedure
progression of atherosclerotic disease
rare; can result in late bypass graft thrombosis
aneurysmal dilation
Indications for surveillance of bypass grafts
acute onset of pain
diminished or absent pedal pulses
persistent nonhealing ulcers
recent history of loss of limbing or swelling
ABI falls greater than 0.15
Early postoperative baseline ultrasound
Routine intervals for surveillance of bypass grafts
3, 6, 12 months and annually thereafter
minimal required documentation of grayscale, color flow, and spectral Doppler of graft examination
inflow artery
proximal anastamosis
mid-graft
distal anastamosis
outflow artery
Required documentation of stenotic areas
before stenotic region
area of greatest velocity shift
distal to stenotic region
Spectral analysis angle should be approximately ___ degrees.
60
What is “walking through” a stenosis?
spectral analysis with greatest Doppler shift as well as proximal and distal to area
End to end anastamosis allows for flow down bypass conduit as well as some flow to be maintained within native distal artery
inflow vessel
Typically a change in caliber as one moves from the inflow artery through the anastamosis and into proximal segment of bypass that results in a small disruption of laminar flow profile
proximal anastamosis
The _____ anastamosis may exhibit mild turbulence caused by geometry of anastamosis and slight disruption in laminar flow
distal
Primary goal bypass graft ultrasound
document anatomic and hemodynamic characteristics of the bypass graft and adjacent vessels
clearly visible if bypass graft is perpendicular to ultrasound beam
intimal-medial layer
Normal walls of vein graft
smooth and uniform
uniform echogenicity plaque
homogeneous plaque
mixed level echoes within plaque
heterogeneous plaque
bright white echoes that cause acoustic shadowing
calcifications
surface characteristics of plaque
smooth surfaced
irregularly surfaced
Two most common image abnormalities of graft ultrasounds
valves or valve remnants
myointimal hyperplasia
incomplete valve disruption during surgery
valve remnants
typically takes place in areas where vein has sustained injury at site of valve sinus
myointimal hyperplasia
rapid proliferation of cells into intimal layer of cellwall which can result in stenosis
myointimal hyperplasia
small, confined projections into vessel lumen made up of a segment of vessel wall that has separated from the rest of the wall
intimal flap
intimal flap that progresses over several centimeters
dissection
can occur adjacent to a suture line
aneurysmal dilatation
Aneurysmal dilatation requires the vessel to be ___ times greater than caliber of adjacent vessel
1.5
Pseudoaneurysms most often form at _______.
anastamotic sites
Common site of pseudoaneurysm
CFA in groin at outflow of a prosthetic aortofemoral or femofemoral crossover graft
Normal bypass grafts waveforms
multiphasic with a sharp upstroke and a narrow systolic peak; reversed flow during diastole
A normal bypass graft waveform is indicative of a normal ___ resistance peripheral arterial bed
high
complication unique to in situ bypass grafts
arteriovenous fistula
occurs when a tributary of great saphenous vein connects, directly or indirectly, via a perforator with deep venous system and is left unligated after creation of bypas
arteriovenous fistula
Doppler spectrum bypass graft proximal to level of fistula
constant antegrade flow
Doppler spectrum bypass graft distal to level of fistula
no or little diastolic flow
Energy losses across a stenosis will produce _____ velocities distal to a stenosis and result in a broadened peak.
lower
2 main criteria characterizing a stenosis
measurement of PSV
calculation of velocity ratio
Normally functioning bypass grafts PSVs
less than 150 cm/s
PSV cutoff for an abnormality
greater than 180 cm/s
measured by dividing maximum PSV at stenosis by PSV obtained just proximal stenosis
velocity ratio
doubling is PSV compared to adjacent more proximal segment
50% or greater stenosis
Stenosis range
180 cm/s - 300 cm/s
75% or greater velocity ratio
3.5
PSV greater than 300 cm/s
75% or greater stenosis
calculated by taking an average of 3-4 PSV values in nonstenotic segments
Mean graft flow velocity (GFV)
Normal GFV
greater than 40 cm/s
A decrease in GFV indicates:
bypass in jeopardy of failure
Which of the following is NOT considered a method of assessment of a lower extremity infraguinal bypass graft?
a. physical/clinical evaluation
b. ankle to brachial index
c. chemical blood chemistry panel
d. plethysmography
c
Which vein would typically be used for an in situ bypass in the lower extremeity?
the great saphenous vein
What is an advantage of synthetic grafts when compared to autogenous vein grafts?
low rate of early technical problems
Why are in situ infrainguinal bypass grafts using the great saphenous vein a common and preferred technique?
there is a better match of vessel size at the inflow and outflow
What is the term to describe an autogenous vein graft in which the vein retains its original anatomical direction?
orthograde
Independent of the type of bypass graft used, where is the distal anastamosis typically located?
distal to the disease
Which of the following is NOT one of the main causes for early autogeneous vein graft thrombosis (within the first 30 days)?
a. underlying hypercoagulable state
b. myointimal hyperplasia
c. inadequate vein conduit
d. inadequate run-off bed
b
After 24 months, what is the likely cause of stenosis in the inflow or outflow vessels?
progression of atherosclerotic disease
At a minimum, which physiologic test should be included when assessing a lower extremity bypass graft?
PVR waveformswith thigh high and below knee pressures
Which artery is NOT commonly used as inflow for a bypass graft in the lower extremities?
a. common femoral artery
b. profunda femoris
c. geniculate artery
d. popliteal artery
c
Which transducer would allow optimal near-field imaging for the evaluation of a superficial, in situ vein graft?
a. 2 to 3 MHz
b. 3 to 5 MHz
c. 5 to 7 MHz
d. 10 to 12 MHz
d
What views can be used for an initial rough scan of a bypass graft, including inflow and outflow, and may be helpful to identify tributaries of an in situ graft?
transverse
Which of the following is NOT a potential incidental finding related to the perigraft space?
a. retained valve
b. seroma
c. hematoma
d. abscessses
a
Where will myointimal hyperplasia typically occur in an autogenous vein graft>
at the distal anastamosis
If an intimal flap or a dissection is present in a bypass graft, what is the typical cause?
intraoperative technical problem
In synthetic aortofemoral or femoro-femoral grafts, where may pseudoaneurysms, although rare, occur?
the distal anastamosis
Arteriovenous fistulae, occasionally seen in in situ bypass grafts, result from failure to ligate which of the following?
a. the small saphenous vein
b. a perforating vein
c. a small arterial branch
d. a defect at valve lysis
b
How is mean graft flow velocity calculated?
averaging three or four velocities from nonstenotic segments
What is the first modality that hsould be used to examine a bypass graft?
B-mode
On a follow-up of a bypass graft done 4 years ago, what may a Doppler spectrum displaying delay in systole indicate?
atherosclerotic stenosis at the inflow
Duplex ultrasound has been shown to be reliable in the detection of significant pathology in infrainguinal bypass grafts in ______ patients, before measurable changes in physiologic testing.
asymptomatic
Combining physiologic study data with duplex ultrasound for the assessment of an infrainguinal bypass graft is important for the detection of significant pathology and the evaluation of _____.
global limb perfusion
Types of bypass grafts can be categorized based on the material used for the graft and ______ employed.
surgical technique
Vein grafts have a longer patency rate than synthetic grafts (independently of the location) because vein grafts are less _______.
thrombogenic
Types of materials used for infrainguinal bypass grafts include autogenous veins, synthetic materials, and _______.
cryopreserved
Within the first 30 days of the perioperative period following the implantation of a bypass graft, the most common problems are ______.
technical
In the 1 to 24 month postoperative period, 75% of graft revisions are done for stenoses at the proximal or distal ______.
anastamosis
To document a stenosis within a bypass graft most completely, the PSV and EDV proximal, within, and distal to the stenosis should be noted as well as poststenotic _____.
turbulence
To ensure accurate documentation during a follow up for a bypass graft, it is important for the sonographer to be familiar with the type and location of the bypass and, therefore, refer to _____.
surgical notes
Twenty four months after a bypass graft has been performed, the main cause of failure will be _______, primarily in the inflow and outflow arteries.
progressive atherosclerosis
During follow-up exams of bypass graft using comparison of flow velocities for diagnostic purposes, an effort should be made to obtain the velocities in the same location, as well as with the same _____ as previously employed.
angles
When evaluating the distal anastamosis and outflow artery of a bypass graft, a(n) ______ in peak systolic velocity (PSV) in the outflow artery can be encountered because the artery may have a smaller caliber.
increase
Within the vein conduit, the two most common image abnormalities that are observed are _____ and ____.
valves
myointimal hyperplasia
Color Doppler can be useful in the evaluation of a bypass for defects; however, care must be taken because color can also _____ small wall defects or other pathology.
mask
Although located in the lower extremities, Doppler spectra in a bypass graft can display ____ resistance characteristics, often owing to hyperemia or arteriovenous fistula.
low
A blunted, monophasic spectral Doppler pattern with zero diastolic flow typically indicates ______.
stenosis
A decrease of mean graft flow velocity of more than _____ from previous exam is indicative of potential failure of the graft.
30 cm/s
A velocity ratio of 3.5 and a PSV >300 cm/s is consistent with a ____ stenosis.
> 75%
A tunnel PTFE femoral to popliteal graft will be _____ than an in situ graft.
deeper
To examine the distal anastamosis and outflow of a femoral to dorsalis pedis bypass graft, one may opt to select a transducer with ____ frequency.
higher
An in situ graft vein refers to:
a vein left in its natural anatomic bed
The distal anastamosis of a bypass is generally constructed:
below the level of the most distal site of arterial disease
A patient presents with right foot pain following a right lower extremity in situ bypass 2 weeks ago. Which of the following is least likely to be observed during a duplex ultrasound scan?
a. anastomotic stricture due to suture placement
b. thrombosis
c. a partial valve remnant
d. progression of atherosclerotic plaque
d
All of the following statements concerning myointimal hyperplasia are true except:
a. will have a different ultrasound appearance than plaque
b. can become evident on ultrasound between 1 and 24 months
c. is not atherosclerotic plaque
d. only occurs at valve sites
d
Which of the following transducers should be selected to examine a tunneled synthetic graft?
a. 7-10 MHz linear array
b. 5-7 MHz linear array
c. 10-15 MHz hockey stick type transducer
d. 10-12 MHz linear array
b
You are asked to examine a patient who has a common femoral to below knee popliteal artery bypass graft. Which of the following lists some of the segments that must be included in the examination?
a. the common femoral, distal popliteal, and distal posterior tibial arteries
b. the common femoral, proximal superficial femoral, and proximal profunda femoral arteries
c. The common femoral, distal anastamosis, and mid to distal posterior tibial arteries
d. the common femoral, proximal anastamosis, distal popliteal arteries
d
Proximity to the bypass graft is particularly important to note for which of the following incidental pathology?
a. abscess
b. dilated lymph nodes
c. venous thrombosis
d. none
a
An intimal flap is a complication that can be seen with bypass grafts. It should appear as:
a small piece of the vessel wall which projects into the lumen of the
Which of the following anastamotic sites is the most common location for pseudoaneurysm formation?
a. a common femoral to saphenous vein in situ bypass graft
b. A saphenous vein in situ bypassgraft to mid posterior tibial artery
c. a common femoral artery to prosthetic graft
d. a vein-vein interposition graft
c
During a 6 month postoperative ultrasound examination of an in situ bypass, you observe the spectrumin the proximal bypass as having a sharp rise to peak systole and continuous antegrade flow throughout diastole. The most likely cause for this waveform includes:
a
A 50% stenosis within a bypass is most likely associated with which of the following?
a. a verlocity ratio of >2.0
b. an end diastolic velocity of > 20 cm/s
c. A peak systolic velocity os >125 cm/s
D. A velocity ratio of >1.5
a
Which of the following correclty desribes the calculation of mean graft flow velocity
a. average the volume flow meausmrents, taken at the prroximal and distal portions of the bypass graft
b. average 3 to 4 peak systolic velocity measurements in nonstenotic segments of a bypass graft
c. average 3 to 4 peak systolic velocity measurements taken within a stenotic segmentof the bypass graft \
d. average the volume flow measurements taken at 3 to 4 different segments of the bypass graft
b
As compared to a previous examination, which statement is correct concerning mean graft flow velocity?
a. a decrease greater than 30 cm/s indicates a bypass may by in jeopardy of failure
b. cannot be used to compare bypass status between visits
c. A decrease greater than 0.15 indicates a bypass may be in jeopardy of failur
d. An increase greater than 2.0 indicates a 50% stenosis is likely present
a
What finding is observed in all bypass stenoses?
poststenotic turbulence
You are examining a patient who is 3 years postop with a superficial femoral to peroneal artery in situ bypass. The patient is cocmplainging of calf pain when walking. Which of the following is most likely the cause of this patient’s symtptoms.
a. graft entrapment
b. poor graft flow due to an arteriovenous fistula
c. progression of atherosclerotic disease within the inflow or outflow arteries
d. A stenosist due to suture placement
c
made of various manufactured materials; associated with poor long-term patency rates
prosthetic (synthetic) bypass grafts
preferred graft material; better long-term patency rates
autogenous vein
Most common vein used for bypass grafts
great saphenous
During the first 30 days, _____ problems are more likely to occur
technical
Between 1 and 24 months, _____ can developing creating stenosis and usually occurs at ______.
myointimal hyperplasia
valve site
Most common cause of graft revision between 1 and 24 months
myointimal hyperplasia
Routine surveillance protocol bypass graft
early first postoperative ultrasound, first year 3, 6, 12 months and annually thereafter
Normal walls of vein graft should appea:
smooth and uniform
_____ grafts have a distinctive double line appearance of graft wall.
PTFE
valve or valve remnants that remain due to incomplete valve disruption during surgery; appear as bright echoes within graft lumen
retained valves
rapid proliferation of cells into intimal layer; can occur at any point along bypass conduit; typically occurs in areas where vein has sustained injury or valve sinus; can result in stenosis
myointimal hyperplasia
A normal bypass should demonstrate _____ waveforms with ____ upstroke and _____ systolic peak
multiphasic
sharp
narrow
abnormal connection between artery and vein
arteriovenous fistula
Energy losses across stenosis produce lower velocities ____ to stenosis.
distal
Normal velocities are typically below _____ cm/s
150
PSV >___ cm/s considered abnormal
180
calculated by taking average of three to four PSV values in nonstenotic grafts segments at various levels
mean graft flow velocity
Normal GFV is greater than ___ cm/s
45
