Deep Venous Thrombosis - DVT

Doctor examining woman's leg
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Deep venous thrombosis (DVT) is a condition in which blood clots form in the deep leg veins. DVT is significant for two reasons: The DVT itself can cause severe symptoms, and the DVT often leads to the life-threatening condition of pulmonary embolus.

DVT can occur either in the veins above the knee (that is, in the ileofemoral veins of the groin and thigh area) or in the veins below the knee (that is, in the calf veins).

The risk of pulmonary embolus is much lower when DVT is isolated to the calf area.

Who Gets DVT?

DVT is most often seen in people who have been immobile for long periods of time, for instance, following recent surgery, stroke, paralysis, or recovery from trauma. DVT also occurs more frequently in people with malignancy or heart disease, and (especially in women) in the obese and in smokers. The use of birth control pills and hormone replacement therapy significantly increases the risk of DVT.

Symptoms of DVT

The most common symptoms of DVT are swelling, pain and redness in the affected leg. These symptoms can vary from mild to disabling.

Diagnosing DVT

When DVT is present, immediate treatment with anticoagulation therapy (see below) will markedly reduce symptoms, as well as the odds of developing pulmonary embolus. However, the same symptoms seen with DVT also occur in a number of other medical conditions -- including skin infections, muscle tears, several kinds of knee conditions, and inflammation of the superficial leg veins -- and the treatment for all these conditions are different.

So, whenever DVT is suspected, it becomes important to make a definitive diagnosis.

In the past, making a firm diagnosis of DVT required an invasive procedure called venography, in which dye was injected into the leg veins, and x-ray images were made, looking for obstructions caused by blood clots. Fortunately, the need for venography has been almost completely replaced in recent years by the availability of two non-invasive tests -- impedance plethysmography and compression ultrasound.

In impedance plethysmography, a cuff (similar to a blood pressure cuff) is placed around the thigh and inflated, in order to compress the leg veins. The volume of the calf is then measured (by means of electrodes that are placed there). The cuff is then deflated, allowing the blood that had been "trapped" in the calf to flow out through the veins. The calf volume measurement is then repeated. If DVT is present, the difference in volume (with cuff inflated versus cuff deflated) will be less than normal -- indicating that the veins are partially obstructed by a blood clot.

Compression ultrasound is a variation of the commonly used ultrasound technique, in which sound waves are applied to tissue by means of a probe, and an image is constructed from the returning sound waves. In compression ultrasound, the ultrasound probe is placed over the vein, and an ultrasound image of the vein is produced. The vein is then compressed (by pushing on it with the ultrasound probe). If DVT is present, the vein is relatively "firm" (because of the presence of a clot), and its compressibility is reduced.

When DVT is suspected, the diagnosis can usually be confirmed or rejected by using either one of these noninvasive tests.

Because relatively few hospitals commonly perform plethysmography, while every modern hospital performs scores of ultrasound tests each day, the compression ultrasound test is more commonly used for diagnosing DVT.

Treatment of DVT

The basic treatment of DVT is the use of anticoagulant drugs ("blood thinners"), both to prevent further blood clotting in the leg veins, and to reduce the chances of developing a pulmonary embolus.

As soon as DVT is diagnosed, it is generally recommended that therapy be started immediately with one of the derivatives of heparin (such as Arixtra, or fondaparinux) that can be given by subcutaneous (under the skin) injections.

These drugs provide an immediate anticoagulation effect.

Once this acute therapy is begun, more chronic treatment with Coumadin can be started. It usually takes several days to a week or more before Coumadin becomes completely effective, and its correct dosage has been determined. Once the Coumadin dosage has been adjusted and the drug is working optimally, the heparin derivative can be stopped.

While the newer anticoagulation drug Pradaxa (dabigatran) has been tested in patients with DVT and appears effective, it has not yet been approved by the FDA for this use.

Anticoagulation therapy for DVT is usually continued for at least three months. If DVT is recurrent, if the underlying cause (such as heart failure) is still present, or if a large pulmonary embolus has occurred, treatment is usually continued indefinitely.

In addition to anticoagulation, it is important for people with DVT to walk frequently, and to avoid situations where they will need to remain seated for prolonged periods of time. Compression stockings, which help the leg veins return blood back to the heart, are also helpful, and should be strongly considered for at least two years after DVT has occurred.

With adequate treatment, most people who have DVT can recover completely.


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Goodacre S. In the clinic. Deep venous thrombosis. Ann Intern Med 2008; 149:ITC3.