Ultrasound Assessment of Arterial Bypass Grafts Workbook and Outline

What is bypass?

A channel that diverts blood flow from one artery to another, usually done to shunt flow around an occluded portion of a vessel

What is a graft?

A conduit that can be prosthetic material or autogenous vein used to divert blood flow from one artery to another

What is an in situ bypass?

The great saphenous vein is left in place in its normal anatomical position and used to create a diversionary channel for blood flow around an occluded artery.

What is anastomosis?

A connection created surgically to connect two vessels that were formerly not connected

What is an arteriovenous fistula?

A connection between an artery and a vein that was created because of surgery or by other iatrogenic means

What is hyperemia?

An increase in blood flow. This can occur following exercise. It can also occur following restoration of blood flow following periods of ischemia.

Which of the following is NOT considered a method of assessment of a lower extremity infrainguinal bypass graft?

a. physical/clinical evaluation

b. ankle to brachial index

c. chemical blood chemistry panel

d. plethysmography

c. chemical blood chemistry panel

Which vein would typically be used for an in situ bypass in the lower extremity?

a. the cephalic vein

b. the basilic vein

c. the small saphenous vein

d. the great saphenous vein

d. the great saphenous vein

What is an advantage of synthetic grafts when compared to autogenous vein grafts?

a. high thrombogenic potential

b. low rate of early technical problems

c. high rate of progressive stenosis at the inflow artery

d. high long-term patency rate

b. low rate of early technical problems

Why are in situ infrainguinal bypass grafts using the great saphenous vein a common and preferred technique?

a. There is a better match of vessel size at the inflow and outflow.

b. There is no need to lyze the valves.

c. The branches of the great saphenous vein provide additional collateral.

d. This allows for reverse flow.

a. 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?

a. reverse

b. antegrade

c. orthograde

d. retrograde

c. orthograde

Independent of the type of bypass graft used, where is the distal anastomosis typically located?

a. distal to the disease

b. proximal to the disease

c. at the level of the popliteal artery

d. at the level of the dorsalis pedis

a. distal to the disease

Which of the following is NOT one of the main causes for early autogenous 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. myointimal hyperplasia

After 24 months, what is the likely cause of stenosis in the inflow or outflow vessels?

a. myointimal hyperplasia

b. retained or improperly placed suture

c. progression of atherosclerotic disease

d. graft entrapment

c. progression of atherosclerotic disease

At a minimum, which physiologic test should be included when assessing a lower extremity bypass graft?

a. full segmental pressure exam with CW Doppler waveforms

b. PVR waveforms only

c. PVR waveforms with high thigh and below-knee pressures

d. ankle-brachial index

d. ankle-brachial index

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. geniculate artery

Which transducer would allow optimal near-field imaging for the evaluation of a superficial, in situ vein graft?

a. 2 to 3 MHz sector

b. 3 to 5 MHz curvilinear

c. 5 to 7 MHz linear

d. 10 to 12 MHz linear

d. 10 to 12 MHz linear

What view 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?

a. sagittal

b. coronal

c. transverse

d. long-axis

c. transverse

Which of the following is NOT a potential incidental finding related to the perigraft space?

a. retained valve

b. seroma

c. hematoma

d. abscesses

a. retained valve

Where will myointimal hyperplasia typically occur in an autogenous vein graft?

a. at the proximal anastomosis

b. at the distal anastomosis

c. at a site of previous valve sinus

d. in the midgraft only

c. at a site of previous valve sinus

If an intimal flap or a dissection is present in a bypass graft, what is the typical cause?

a. valve retention

b. intraoperative technical problem

c. fibrosis in the inflow artery

d. aneurysms at the distal anastomosis

b. intraoperative technical problem

In synthetic aortofemoral or femoro-femoral grafts, where may pseudoaneurysms, although rare, occur?

a. the midgraft

b. anywhere along the length of the graft

c. the proximal anastomosis

d. the distal anastomosis

d. the distal anastomosis

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. a perforating vein

How is mean graft flow velocity calculated?

a. taking several measurements at the midgraft level

b. averaging the velocities at the proximal and distal anastomoses

c. averaging the velocities from the inflow and outflow arteries

d. averaging three or four velocities from nonstenotic segments

d. averaging three or four velocities from nonstenotic segments

What is the first modality that should be used to examine a bypass graft?

a. B-mode

b. spectral Doppler

c. color Doppler

d. power Doppler

a. B-mode

On follow-up of a bypass graft done 4 years ago, what may a Doppler spectrum displaying delay in systole indicate?

a. technical defect at the anastomosis

b. atherosclerotic stenosis at the inflow

c. arteriovenous fistula within the graft

d. imminent failure from distal occlusion

b. 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.

the 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 veins

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 _____________________.

anastomoses

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 _____________________.

postoperative 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.

progression of 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.

angle

When evaluating the distal anastomosis and outflow artery of a bypass graft, a(n) _____________________ in peak systolic velocity 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 _____________________.

distal stenosis or occlusion

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 tunneled PTFE femoral to popliteal graft will be _____________________ than an in situ graft.

deeper

To examine the distal anastomosis and outflow of a femoral to dorsalis pedis bypass graft, one may opt to select a transducer with _____________________ frequency.

higher

What type of waveforms are in a Bypass graft?

multiphasic high resistance

What may be absent in early post op in a bypass graft waveform?

the reversal component

What type of bypass grafts are there?

- prosthetic

- autogenous

What is a prosthetic graft?

- synthetic

- poor long term patency rates

What is an autogenous graft?

- natural

- preferred

- better long-term patency rates

- early failure monitoring

What does in situ placement mean?

vessel remains in orginal position

Where is the in situ placement normally?

GSV

What placement of a graft is the large end of the vein is anastomosed to large end artery or small end to small end?

in situ

What type of placements are there in bypass grafts?

- in situ

- orthograde and retrograde

- GSV removed from natural position

- various locations

When the GSV is removed from the natural position the vein is flipped and valves stay and then the large end vein is anastomosed to what?

the small end artery

How is location of the bypass graft determined?

by level of disease, proximal anastomosis above disease and distal anastomosis below disease

_____ is usually proximal anastomosis

CFA

_____ is usually distal anastomosis

Pop A, ATA, and PTA

What are the common causes of graft failure in the first 30 days?

- retained valve/ leaflet

- intimal flap

- anastomosis

- entrapment

- thrombosis

What are the common causes of graft failure in 1-24 months?

- myointimal hyperplasia (stenosis at anastomosis)

What are the common causes of graft failure in greater than 24 months?

- progression of atherosclerosis

- aneurysm

Most common locations for aneurysm in a bypass graft is?

- conduit

- anastomosis

What are the flow changes in a progression of atherosclerosis with graft failure?

- diastolic change

- increased AT

- decreased PSV

What is the surveillance protocol for bypass graft placements?

at 3 months, 6 months, 9 months and then annually after that

When are more exams require with bypass grafts?

- interoperative revision

- early postop revision/thrombectomy

- limited venous conduits

What are some indications for a bypass graft exam?

- acute onset pain

- dimished/ absent pedal pulses

- non-healing ulcers

- poor ABI

What classifies a poor ABI?

a decrease of over 0.15 between exams

What abnormalities can occur with bypass grafts?

- dissection

- intimal flap

- aneurysms

- pseudoaneurysms

- hematoma

- perigraft fluid collection

What are common incidental findings associated with bypass grafts?

- venous thrombosis

- lymph nodes

- hematoma

- seroma

- absess

What is the waveform distal to a stenosis?

- continous diastolic flow

- delayed systolic peak

- blunted, monophasic with no diastolic flow

What is the waveform proximal to a stenosis?

- abnormally high resistance

- staccato waveform (sharply detached and separated)

Normal graft velocity = ?

<150 cm/s

Abnormal graft velocity = ?

>180 cm/s

PSV of ____ equates to greater or equal to 50% stenosis

2.0

PSV of ____ equates to greater or equal to 75% stenosis

3.5

What is the mean graft velocity (GFV)?

average 3-4 PSV in nonstenotic areas at various levels

Normal GSV = ?

> 45 cm/s

What is the GSV rate for limited outflow?

< 40 cm/s

A decrease GFV rate over ____ indicates pending graft failure

30