Deep Venous Thrombosis (DVT)

Overview

Venous thrombosis is a condition in which a blood clot (thrombus) forms in a vein. Most commonly, venous thrombosis occurs in the "deep veins" in the legs, thighs, or pelvis and is known as a deep vein thrombosis, or DVT.

The most important consequence of a DVT is a pulmonary embolism (PE). The related subject matter of PE will be discussed below.

The term "venous thromboembolism" is sometimes used when discussing both DVT and PE.

Pathophysiology

Deep vein thrombosis of the lower extremity is subdivided into either distal (calf vein) or proximal (thigh) vein thrombosis. They may also be subdivided into either superficial or deep. The most important consequence of DVT’s is a pulmonary embolism. Deep vein thromboses, that are anatomically proximal in nature, are considered to be of more importance clinically, than superficial and/or distal thrombi of the lower extremity. Deep, proximal thromboses are more commonly associated with the serious and possibly fatal outcomes involving pulmonary embolism.

Risk Factors for DVT and PE

There are a number of factors that increase a person's risk of developing a DVT (and possible, a subsequent PE):

• Inherited thrombophilia (genetic predisposition to clot)
• Elevated clotting factors (e.g., increased Factor VIII, an element of clotting)
• Pregnancy
• Obesity
• Surgery (especially those involving hip, pelvis, or knee)
• Prolonged sitting, especially sitting for six or more hours on a plane, or bed rest
• Trauma (especially if blood vessels are injured)
• Smoking
• Heart failure
• Previous DVT or PE
• Increased age
• Cancer — Some cancers increase substances in the blood that cause blood to clot
• Kidney problems, such as nephrotic syndrome
• Certain medications (eg, birth control pills, hormone replacement therapy, erythropoietin, tamoxifen, thalidomide). The risk of a blood clot is further increased in people who use one of these medications and smokes or is overweight.

Clinical Presentation

Classic symptoms suggesting deep venous thrombosis are described as unilateral leg swelling, pain, warmth, and erythema (redness) of the iliac, femoral, or popliteal veins.

Tenderness may be present along the course of the involved veins, and a cord may be palpable.

Diagnosis

The diagnosis of the DVT of the calf is often difficult to make at the bedside, clinically. Increased resistance or pain during dorsiflexion of the foot (Homan’s sign) is an unreliable diagnostic sign. Therefore, a high index of clinical suspicion is required if these signs are not present.

Duplex Venous Ultrasonography is the noninvasive test used most often to diagnosis DVT (i.e., Doppler imaging). By imaging the deep veins, thrombus can be detected either by (1) direct visualization or (2) by inference when the vein does not collapse on compressive maneuvers. The Doppler ultrasound measures the velocity of blood flow in veins.

Other imaging studies that may be utilized to diagnose a DVT include:

• Computed tomography (CT Scan)
• Magnetic resonance imaging (MRI)
• Contrast venography

A blood test called D-dimer, which may be used to diagnose DVT or pulmonary embolus, will be discussed below, under pulmonary embolus, just below.. If a person with a DVT also has signs or symptoms of a pulmonary embolus, additional testing will be required. This will be discussed below.