Lower Extremity Venous Duplex Ultrasound

Background

Diagnostic ultrasonography is the use of ultrasound to image anatomical structures. Ultrasound is sound waves that have a frequency above what the human ear can hear, or higher than 20 × 10 ⁴ Hz. Diagnostic ultrasound is usually on the order of MHz, or 10 ⁶ Hz. These sound waves are generated from an ultrasound probe, which houses a piezoelectric element that vibrates in response to electric current. Ultrasound waves, if aimed at a structure, may be reflected back toward the probe. The received sound waves are transmitted to a computer, which processes them and generates an image. Clinical ultrasonography uses images that are generated by the computer in different modes, including 2-D, M-mode, spectral Doppler, and color Doppler imaging. 2-D imaging is the standard representation of a structure in a two-dimensional view. Spectral Doppler displays velocities of red blood cells in a specified area on a graph over time. Color Doppler imaging displays the direction and speed of blood flow across a displayed area using a color map. A lower extremity venous duplex ultrasound is the application of clinical ultrasonography to the veins of the lower extremity using a combination of 2-D, spectral Doppler, and color Doppler imaging, otherwise known as “duplex” imaging.

How to Use It

Ultrasonography of the lower extremities is imaging that can be used to evaluate venous diseases of the lower extremities. According to the 2019 ACR-AIUM-SPR-SRU Practice Parameter for the Performance of Peripheral Venous Ultrasound Examination, venous ultrasound exams can be used to evaluate for suspected deep venous thrombosis (DVT) or venous obstruction. For patients who are at high risk for DVT, venous ultrasound can be applied for serial DVT evaluation despite a negative initial exam. Venous ultrasound can also be used for the assessment of venous insufficiency, reflux, and varicosities as well as postprocedural assessment of venous ablation. Ultrasound can be used for patient follow-up in those with known venous thrombosis on therapy who undergo a clinical change where a change in thrombus burden will alter treatment. Visualization via ultrasound can also determine a potential source for known pulmonary embolism. In addition, lower extremity venous duplex ultrasound may be used to monitor patients with distal, or infrapopliteal, DVTs to help guide whether they should receive anticoagulation.

How It Is Done

The full lower extremity venous duplex ultrasound exam is done from the inguinal ligament to the ankle. It can be performed either in the inpatient or outpatient setting and requires no sedation or analgesia and no meal restrictions. The common femoral vein, deep femoral vein at the confluence of the femoral vein, great saphenous vein at the sapheno-femoral junction, femoral, popliteal, posterior tibial, and peroneal veins are imaged. When testing for DVT, the veins are tested every 2 cm for compressibility by pressing down on the skin with the ultrasound transducer. Spectral Doppler and color Doppler are used to assess blood flow.

When testing for venous insufficiency, the patient should be standing. If the patient cannot stand, he or she should be placed in >45 degree reverse Trendelenburg position. The leg that is being imaged should not be weight bearing. Reflux should be elicited by using several maneuvers including a calf squeeze then release, manual compression of the vein clusters, pneumatic calf cuff deflation, active foot dorsiflexion and relaxation, and the Valsalva maneuver. The vein should then be imaged in the longitudinal axis using 2-D and spectral Doppler to look for venous flow in the opposite physiologic direction lasting greater than 0.5 seconds. ^,

Medication Implications

While the lower extremity venous duplex ultrasound is noninvasive and requires no pre- or periprocedural medication to be administered, there are many medication implications to consider when a DVT is diagnosed. Anticoagulation for acute symptomatic proximal DVTs is generally indicated because it reduces the incidence of pulmonary emboli and mortality. There are many anticoagulants to choose from and many situations influencing the choice and duration of the anticoagulant.

Patients without cancer who have proximal DVTs should receive anticoagulation for 3 months, preferably using a direct oral anticoagulant (DOAC) such as dabigatran, rivaroxaban, apixaban, or edoxaban over warfarin. In patients with a proximal DVT and cancer, low-molecular-weight heparin (LMWH) is preferred. In patients with DVTs that are provoked, treatment should last for 3 months, assuming the provoking risk factor is no longer present. In patients with DVTs that are not provoked, treatment may need to be longer, to be determined clinically based on bleeding risk. In cancer patients who have a proximal DVT, treatment should be longer than 3 months.

While anticoagulation for acute symptomatic proximal DVTs is clearly indicated to reduce pulmonary emboli and mortality, treatment for distal DVTs is not as clear. Approximately 15% of isolated distal DVTs subsequently extend into the popliteal veins. Therefore, the benefit of anticoagulation must be weighed against the risk of bleeding. In patients with certain risk factors such as having a previous history of venous thromboembolism (VTE), cancer history, or having extensive thrombosis, anticoagulation is indicated. If anticoagulation is not chosen, surveillance with ultrasound should be performed after initial diagnosis of distal DVT. Choosing to neither initiate anticoagulation nor surveil a known distal DVT should not occur. Upon surveillance, if the distal DVT has not extended, the patient should not receive anticoagulation. If the distal DVT has extended, the patient should receive anticoagulation.