Ultrasound signs of peripheral arterial disease

Color duplex sonography in the diagnosis of peripheral arterial disease

Peripheral arterial occlusive disease (PAOD)

Peripheral arterial occlusive disease caused by atherosclerosis is the most common disease of the arteries of the extremities (95%). Color duplex sonography can be used for screening patients with clinical suspicion of peripheral arterial occlusive disease and for control after surgical treatment. About 10% of the population has peripheral circulation disorders, of which 10% have affected arteries of the upper limb, and 90% - of the lower limb (35% - pelvis, 55% leg). Multiple levels and bilateral disease are common. The earliest ultrasound sign of clinically hidden atherosclerosis is intimal and medial thickening. Occlusive disease also manifests itself as wall changes in B-mode (narrowing of the lumen, soft or hard plaques) and turbulence and blood flow changes in color mode. The primary tools for quantifying stenosis are spectral analysis and peak systolic velocity ratio determination.

Stages of chronic occlusive peripheral arterial disease

• Stage I: stenosis or occlusion with no clinical symptoms
• Stage IIa: intermittent claudication, pain-free distance over 200 m
• Stage II b: intermittent claudication, pain-free walking distance less than 200 m
• Stage III: pain at rest
• Stage IVa: ischemia with trophic disorders and necrosis
• Stage IV b: ischemia, gangrene

Leriche syndrome

A specific form of peripheral arterial occlusive disease is Leriche syndrome, which is a chronic thrombosisaortic bifurcation with bilateral absence of femoral pulsation. An extensive collateral network develops to compensate for the occlusion and is usually discovered incidentally in patients being evaluated for intermittent claudication or erectile dysfunction. Note that the decrease in peripheral resistance results in biphasic waves in the inferior epigastric artery, which serves as a collateral.

True aneurysms, pseudoaneurysms, dissecting aneurysms

Key aspects in establishing the diagnosis of aneurysm are determination of the extent of the lesion, assessment of the perfused lumen (thrombi are potential sources of emolitis) and identification of vascular wall dissection. A true aneurysm is a dilation of all layers of the vascular wall. It is most common in the popliteal artery and may be single or multiple.

A false aneurysm or pseudoaneurysm often occurs iatrogenically during arterial puncture, in this case, in the distal segment of the external iliac artery. It can also develop at the sites of sutures after vascular surgery. The main complications of pseudoaneurysms are ruptures and compression of adjacent nerves. The aneurysmal formation contains a perivascular hematoma communicating with the lumen of the vessel. Color duplex sonography usually reveals uniform bilateral blood flow in the neck of the aneurysm. As a form of treatment, a specialist can induce thrombosis of the perfused hematoma by compression under the control of color duplex sonography. Contraindications include the presence of aneurysms along the umbilical ligament, aneurysms greater than 7 cm in diameter, and limb ischemia. Similar results can be obtained with vascular compression using pneumatic equipment (FempStop). The incidence of spontaneous thrombosis of pseudoaneurysms is approximately 30-58%.

Arteriovenous malformations (AVM)

AVMs may be congenital or acquired, for example as a result of puncture (arteriovenous fistula) or vessel trauma (0.7% of cardiac catheterizations). An AVM is an abnormal connection between the high-pressure arterial system and the low-pressure venous system. This results in characteristic flow disturbances and spectral changes in the artery, both proximal and distal to the fistula, as well as on its venous side. With a decrease in peripheral resistance due to blood shunting, the spectrum becomes biphasic proximal to the fistula and triphasic further away. Arterial inflow into the venous part causes turbulence and arterial pulsation, which can be visualized. Significant shunting poses a potential risk of cardiac volume overload.

Arterial compression syndromes

Arterial compression syndromes result from persistent or transient (eg, with changes in body position) narrowing of neurovascular structures due to many causes, resulting in perfusion deficit of the distal vascular bed. Compression of a vascular segment results in intimal lesions predisposing to stenosis, thrombosis, and embolism. The main arterial compression syndromes of the upper limb are thoracic inlet and outlet syndromes. The main manifestation in the lower limb is popliteal snapping syndrome. Contraction of the calf muscles disrupts the connection between the popliteal artery and the middle head of the gastrocnemius muscle, causing compression of the artery. This is the cause of about 40 % of cases of intermittent claudication occurring before the age of 30. Color duplex sonography can determine changes in blood flow during physical activity and the anatomical relationships of vessels and muscles.

Control after bypass anastomosis

Color duplex sonography allows to evaluate the success of bypass anastomosis and to detect possible complications, such as restenosis and occlusion of the bypass vessel at an early stage. It is necessary to evaluate the proximal and distal anastomoses of the vessel to detect blood flow disturbances. Peak blood flow velocity should be measured at three points. Echogenic wallsvascular prosthesis or stent and acoustic shadowing caused by the stent material should not be mistaken for plaque or restenosis.

Vessel-stent junctions and anastomotic suture lines are areas prone to restenosis.

If the spectrum shows low amplitude, pronounced pulsation and a sharp component of reverse blood flow, it is very likely that there is an occlusion. Occlusion of the common femoral artery is manifested by a break in the color blood flow and the absence of spectral signals from it immediately before the bypass anastomosis.

Follow-up after percutaneous angioplasty

Follow-up examination after successful percutaneous transluminal angioplasty shows a significant increase in peak systolic velocity with normal late diastolic flow. The filling of the spectral window occurs because the examination was performed shortly after surgery and sufficient time had not yet passed for intimal effacement, resulting in persistent turbulent flow.

Criteria for bypass stenosis

• Peak systolic velocity < 45 cm/s
• Peak systolic velocity > 250 cm/s
• Changes in peak systolic velocity ratio greater than 2.5 (most reliable parameter for stenoses > 50%)

Causes of restenosis

• Acute thrombosis
• Vessel dissection after angioplasty due to intima-media ruptures
• Under-expanded stent
• Unevenness of the connection of the bypass vessel or stent with the main one
• Myointimal hyperplasia
• Progression of the underlying disease
• Infection

Evaluation of fistulas for hemodialysis

High-frequency linear transducers (7.5 MHz) are used to evaluate arteriovenous fistulas for hemodialysis access. Due to the difficulty of correlating color duplex sonography data with anatomical structures, the examination should be performed in collaboration with the dialysis physician or surgeon. The following protocol is not recommended:

1. When examining the afferent artery, always begin with the brachial artery, which is usually visualized in cross-section. The spectrum should show a flat, low-resistance pattern with clear diastolic flow. If this does not occur, it should be suspected that blood does not have free access to the fistula and blood flow is reduced due to stenosis.
2. Several duplex volumes (at least three, preferably six) should be obtained in the afferent artery. This is best done on the brachial artery a few centimeters above the elbow joint. These measurements are necessary both for monitoring and for general assessment. A blood flow volume of less than 300 ml/min with a Cimino fistula or less than 550 ml/min with a Gore-Tex catheter indicates insufficiency. Accordingly, the lower values for “normal” fistulas are 600 and 800 ml/min.
3. The afferent artery is examined along its course for signs of stenosis (increased blood flow and turbulence). There are no velocity limits that can confirm stenosis. Stenosis is defined by measuring the decrease in cross-sectional area of the vessel relative to the normal prestenotic and poststenotic segments in B-mode. This also applies to stenoses of the venous portion of the fistula. The vein should be examined with a "floating" transducer with very light pressure, since any compression causes significant artifacts. The access vein is examined, like the central veins, for stenosis, aneurysm, perivascular hematoma, or partial thrombosis. As with digital subtraction angiography, quantitative assessment of stenoses is difficult due to the lack of information on the normal state of the lumen width of the access vein. Stenosis is usually located in the following areas:
   • the area of anastomosis between an artery and a draining vein
   • the area from which access usually comes
   • central veins (eg, after placement of a central venous catheter in the subclavian or internal jugular vein)
   • in Gore-Tex fistula: distal anastomosis between the fistula and the draining vein.

Critical assessment

The clinical importance of noninvasive color duplex sonography and MRA has increased due to the absence of ionizing radiation, especially for frequent follow-up examinations, and due to their advantages in patients with contrast allergy, renal failure, or thyroid adenomas.

While digital subtraction angiography is an invasive technique used only for topographic mapping, color duplex sonography can provide additional diagnostic information about stenotic lesions, functional parameters, and the response of surrounding tissues. It can also identify thrombi in aneurysms. In the hands of an experienced specialist, color duplex sonography is a high-quality, noninvasive technique for examining peripheral vessels.

The disadvantages of color duplex sonography, such as limited visualization of vessels located at depth or hidden by calcifications, have been significantly reduced with the introduction of ultrasound contrast agents.

The panoramic imaging technique SieScape in combination with power Doppler significantly improves the documentation of pathological changes affecting a long segment of the vessel. The combination of these techniques can provide a topographic image of vascular changes up to 60 cm in length.

Color duplex sonography often plays a limited role in the study of lower extremity vessels, especially small caliber ones, with multiple plaques and slow blood flow due to multilevel lesions. Digital subtraction angiography in such cases remains the method of choice in the diagnosis of arterial diseases below the knee joint.

In addition to color duplex sonography, alternatives to digital subtraction angiography include gadolinium-enhanced MRI and phase-contrast MRA of peripheral vessels. CT angiography does not play a major role in the examination of peripheral vessels due to artifacts from calcified plaques, the need for high doses of intravenous contrast agents, and high radiation exposure during prolonged examination. It is better used to detect aneurysms in central vessels.

Evaluation of fistulas for hemodialysis

Color duplex sonography is superior to angiography in many ways. Because of its ability to measure blood flow, color duplex sonography can identify the etiologic cause, such as luminal narrowing due to compression by a hematoma. Color duplex sonography also allows for follow-up studies. When blood flow is known, the significance of stenosis can be assessed more easily than with angiography. Therefore, a watch-and-wait approach can be used for moderate to severe stenosis if the fistula blood flow is considered satisfactory.

Initial prospective and randomized studies have shown that regular CDS studies at 6-month intervals with prophylactic dilation of stenoses greater than 50% significantly prolong the usefulness of hemodialysis access and reduce the cost