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Much debate has surrounded the shape of the CFA waveform as an indicator of iliac artery or inflow disease. A study by Sensier et al (1998) demonstrated that qualitative assessment of the CFA Doppler waveform has a sensitivity of 95%, a speci- ficity of 80% and an accuracy of 87% for the predic- tion of significant aortoiliac artery disease. This study therefore suggests that observation of the CFA wave- form shape is a useful technique for the investigation of inflow disease. The presence of triphasic flow with a short systolic rise time is an indicator of normal inflow. However, care should be exercised when investigating younger patients, who may have a very short proximal iliac stenosis, as the arterial waveform shape may have recovered at the level of the CFA, appearing normal. Marked damping of the CFA waveform with an increase in systolic acceleration time is a good indicator of severe inflow disease. Perhaps the most confusing situation occurs where the inflow arteries are normal but the SFA is occluded and the profunda femoris artery is severely stenosed. This can give rise to a monophonic wave- form pattern in the CFA with a high end diastolic velocity, although the systolic acceleration time remains short. A great deal of care should be used in interpreting flow patterns in this situation.
Areas of aneurysmal dilation typically demonstrate a reduction in peak systolic velocity, frequently asso- ciated with disturbed flow patterns.
ASSESSMENT OF ARTERIAL STENTS
Arterial stents are used to prevent re-stenosis, although there is limited published evidence to demonstrate that they are any more effective than standard angioplasty at maintaining long-term vessel patency. Stents are mainly deployed in the aortoiliac arteries and proximal CFA, although they are also used in the SFA and popliteal artery. Stents are avail- able in different lengths and sizes, and multiple stents can be deployed if the disease is very extensive. They are usually visible on the B-mode image, producing a stronger reflection compared to the arterial wall. The cross-hatched, or lattice, metal structure can often be identified. It is sometimes possible to see nipping of the stent if the atheroma in the artery is very calcified or fibrous and has not been completely compressed to the vessel wall. Color flow imaging
stricture in a CFA stent caused by intimal hyperplasia. The stent walls are clearly visible (arrows).
DUPLEX ASSESSMENT OF LOWER LIMB ARTERIAL DISEASE
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Figure 9.21 Color flow imaging demonstrates a long
and spectral Doppler can be used to assess the flow across the stent (Fig. 9.21). It is not uncommon to find some localized flow disturbance in the region of the stent due to the step between the arterial wall and proximal and distal ends of the stent. Spectral Doppler should be used to grade the degree of any in-stent stenosis using the same criteria as used for grading lower limb disease. Stents placed in arteries close to joints, such as the CFA or popliteal artery, can be stressed by joint movement and may kink or bend. Localized aneurysms can be excluded by inserting a covered stent across the aneurysm; this is discussed in Chapter 11.
OTHER ABNORMALITIES AND SYNDROMES
Lower limb symptoms in younger patients are some- times due to inflammatory or small vessel disorders, such as Buerger’s disease. Flow recordings are nor- mal in the larger arteries proximally, but the distal vessels in the calf may demonstrate low-flow, high- resistance waveforms.
Popliteal entrapment syndrome
Popliteal entrapment syndrome is also a rare but potential cause of claudication and possible distal embolization due to arterial wall damage. In this situation, the popliteal artery follows an anomalous course below the knee and is trapped by the heads of the gastrocnemius muscle during plantar flexion. The popliteal artery can also be trapped by fibrous bands in this area. To test for popliteal entrapment