Deep-Vein Thrombosis (DVT) and Pulmonary Embolism (PE)

Compiled by the American Public Health Association

Deep-vein thrombosis, or DVT, is a common but under-diagnosed medical condition. More people suffer from DVT annually than heart attack and stroke combined!  It occurs when a thrombus (blood clot) forms in one of the large veins, usually in the lower limbs, leading to either partially or completely blocked circulation.  The condition may result in health complications and death if not diagnosed and treated efficiently and effectively.  Although DVT itself may not be life threatening, it may lead to a potentially fatal pulmonary embolism.  It is estimated that venous thromboembolism may contribute to 60,000 - 200,000 deaths each year in the United States, which is more than the number of Americans who die each year from AIDS, breast cancer, or highway accidents.

Deep-vein thrombosis, or DVT, is a common but under-diagnosed medical condition. More people suffer from DVT annually than heart attack and stroke combined.  It occurs when a thrombus (blood clot) forms in one of the large veins, usually in the lower limbs, leading to either partially or completely blocked circulation.  The condition may result in health complications and death if not diagnosed and treated efficiently and effectively.

Venous thromboembolism, or VTE, refers to two serious conditions: deep-vein thrombosis (DVT) and pulmonary embolism (PE).   Although DVT itself may not be life threatening, it may lead to a potentially fatal pulmonary embolism.  Published studies estimate the incidence of venous thromboembolism to be between 200,000 to 600,000 cases annually, and may contribute to 60,000 - 200,000 deaths each year in the United States.

Venous thrombosis in the lower limb can involve the superficial leg veins; the deep veins of the calf (calf vein thrombosis); the more proximal veins, including popliteal veins; the superficial femoral, common femoral, and iliac veins.  Less commonly, thrombosis involves other veins in the body.  Unlike the superficial veins just below the skin surface, most of the deep veins are surrounded by powerful muscles that contract to force blood back to the heart.  One-way valves inside the veins prevent backflow of blood between muscle contractions.  When the rhythm of circulation slows down due to illness, injury, or inactivity, there may be a tendency for blood to accumulate or "pool." A static pool of blood provides an ideal environment for clot formation.

Certain individuals may be at increased risk for developing DVT, although DVT can occur in almost anyone. Some risk factors or triggering events include:

• Acute medical illness
• Surgery, including orthopedic surgeries such as joint replacements, who remain immobile in bed after an operation
• Cancer and chemotherapy treatment
• Chronic heart or respiratory failure
• Paralysis
• Obesity
• Smoking
• Pregnancy
• Use of birth control pills
• Postmenopausal hormone replacement therapy
• Advanced age
• Immobility caused by long-distance travel
• Thrombophilia, an inherited predisposition to clotting

Symptoms of DVT may include pain, swelling, tenderness, discoloration or redness of the affected area, and skin that is warm to the touch. However, up to half of all DVT episodes produce minimal symptoms or are completely "silent."

Because a number of other conditions, including muscle strains, skin infections, and phlebitis (inflammation of veins), display symptoms similar to those of DVT, the condition may be difficult to diagnose without specific tests.

How is Deep-Vein Thrombosis Diagnosed?

Although a number of tests have been evaluated over the years, only three have been shown to have special value for diagnosing DVT in symptomatic patients: venography, impedance plethysmography (IPG), and venous ultrasonography.

• Venography is performed by injecting radiographic material into a superficial vein on the top of the foot. The contrast material mixes with the blood and flows through the leg. An x-ray image of the leg and pelvis will show the calf and thigh veins, which drain into the external iliac vein. A clot is diagnosed by the presence of an intraluminal filling defect, an abrupt cut-off of the contrast material on the x-ray.
  
  
• Impedance plethysmography (IPG) is performed by placing two sets of electrodes around the patient's calf and an oversized blood pressure cuff around the thigh. The electrodes sense a change in blood volume (increased blood volume decreases electrical impedance) in the calf veins, which is recorded on a strip chart. Changes in venous filling are produced by inflating the thigh cuff to obstruct venous return and then reestablishing blood flow by deflating the cuff and assessing the time taken for venous volume in the calf to return to baseline. If a clot is present in the popliteal or more proximal veins, venous emptying is delayed.
  
  
• Venous Ultrasonography of the venous system is obtained with high-resolution equipment to produce two-dimensional images of reflected signals from an array of ultrasound sources, including the common femoral vein in the groin and the popliteal vein, which connects to the femoral vein. Gentle pressure is applied with the probe to determine whether the vein under examination is compressible. The most accurate ultrasonic criterion for diagnosing venous thrombosis is non-compressibility of the venous lumen (cavity) under gentle probe pressure.

The major risk associated with DVT is the development of a pulmonary embolism.  PE can occur when a fragment of a blood clot breaks loose from the wall of the vein and migrates to the lungs, where it blocks a pulmonary artery or one of its branches.

Blockage of the main pulmonary artery by one or more of the emboli may be life threatening. Symptoms may include shortness of breath, a feeling of apprehension, rapid pulse, sweating, and/or sharp chest pain that worsens with deep breathing. Some patients may cough bloody sputum, while others may develop very low blood pressure and pass out.

Between 60,000 and 200,000 people may die of a pulmonary embolism.  This number exceeds the number of Americans who die each year from AIDS, breast cancer, or highway accidents.

Primary prevention measures for DVT may include at-risk patient identification, and a proper diet and exercise regime.  Effective prophylaxis and treatment options exist for both deep-vein thrombosis and pulmonary embolism.

Anticoagulants, or blood-thinning drugs, are commonly used to reduce the risk of and treat DVT.  These agents work by altering the body's normal blood-clotting process and may help to reduce the risk of PE.  Either modulating activation of blood coagulation or preventing venous stasis achieves this prophylaxis.  Low-dose subcutaneous heparin, intermittent pneumatic compression of the legs, oral anticoagulants, adjusted doses of subcutaneous heparin, graduated compression stockings, and low-molecular weight heparins (LMWHs) have shown positive results in reducing PE.

For more information on DVT, click here.

Created: 2/27/2003  -  American Public Health Association
Reviewed: 2/27/2003  -  Donnica Moore, M.D.