How to evaluate lower extremity stents and bypass grafts on ultrasound
Oftentimes, patients will have stents or bypass grafts placed as part of a treatment, so it’s important to be able to recognize them on ultrasound. Let’s dive into how to find and evaluate stents and bypass grafts on duplex ultrasound.
Lower extremity stents on duplex ultrasound
On ultrasound, stents appear with bright and echogenic borders. Stents are most easily recognized at their proximal attachment.
Occasionally, it can be difficult to find and evaluate stents for patency due to the presence of calcific shadowing. The calcific shadowing is from atherosclerotic plaque that is pushed up against the walls of the artery.
Figure 1. Stents can be recognized on ultrasound by their bright and echogenic borders. Sometimes, calcific shadowing from atherosclerotic plaque can make stents difficult to identify, as demonstrated in this superficial femoral artery stent.
When off-axis, you can usually recognize a stent on ultrasound by its mesh pattern.
Figure 2. A stent can often be recognized on ultrasound by its characteristic mesh pattern.
Check out this short video snippet from our Ultrasound Masterclass: Arteries of the Legs Course to see how to identify a stent by its mesh pattern:
The evaluation of a stent follows a standard protocol where a series of velocities are measured in seven key locations:
- Just proximal to the proximal attachment (e.g., inflow).
- Within the proximal attachment.
- In the proximal portion of the stent.
- In the middle of the stent.
- In the distal portion of the stent.
- Within the distal attachment.
- Just distal to the distal attachment (e.g., outflow).
The inflow velocity taken just proximal to the proximal attachment serves as the reference velocity. The velocities are then used to assess the degree of obstruction within the stent.
Figure 3. When evaluating a stent on ultrasound, start by taking the velocity just proximal to the proximal attachment of the stent.
Lower extremity bypass grafts on duplex ultrasound
Finding synthetic bypass grafts
Synthetic bypass grafts (BPGs) are usually easy to recognize on ultrasound. A synthetic BPG looks like a vessel with the same color fill and waveforms as a normal, healthy artery. But, it has patterned edges. Bypass grafts in the superficial femoral artery (SFA) often have a more superficial path compared to the SFA.
Bypass grafts are examined the same way as stents. The only difference is that we use slightly different terminology. Instead of attachments, we use the terms proximal anastomosis and distal anastomosis for the ends of the graft.
Figure 4. A synthetic bypass graft looks like a healthy vessel on duplex ultrasound and has normal waveforms. But, it can be identified by its patterned edges.
Finding autologous bypass grafts
If the graft is autologous (e.g., taken from the patient’s body) from a reversed saphenous vein, there is nothing remarkable about the wall’s appearance. In this case, it is best identified by its pulsating color and location down the length of the medial thigh. In some rare cases, bypass grafts can run down the outer thigh to the anterior tibial artery.
Figure 5. An autologous bypass graft looks just like a normal, healthy vessel on two-dimensional and color flow ultrasound images. It can be identified by its pulsating color and location down the length of the medial thigh.
Some surgeons tend to place the graft in the native artery’s anatomical location—which can be confusing at first. Sometimes you can see the diseased vessel, but it might be difficult to see if the vessel is chronically occluded.
It’s easiest to locate the bypass graft at its proximal anastomosis, which is often in the groin. Once identified, follow the graft continuously like you would with a non-bypassed artery. If you get lost, go back in into a transverse orientation with color to relocate the vessel.
Evaluating bypass grafts
The evaluation of a bypass graft follows the same standard protocol that is used for stents. Measure a series of velocities in seven key locations:
- Just proximal to the proximal anastomosis.
- Within the proximal anastomosis.
- In the proximal portion of the graft.
- In the middle of the graft.
- In the distal portion of the graft.
- Within the distal anastomosis.
- Just distal to the distal anastomosis.
The inflow velocity taken just proximal to the proximal anastomosis is the reference velocity. The velocities are then used to assess the degree of obstruction within the bypass graft.
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