Introduction to deep vein thrombosis (DVT)

Arteries have thin muscles within their walls to be able to withstand the pressure of the heart pumping blood to the far reaches of the body. Veins don't have a significant muscle lining, and there is nothing pumping blood back to the heart except physiology. Blood returns to the heart because the body's large muscles squeeze the veins as they contract in their normal activity of moving the body. The normal activities of moving the body returns the blood back to the heart.

There are two types of veins in the leg; superficial veins and deep veins. Superficial veins lie just below the skin and are easily seen on the surface. Deep veins, as their name implies, are located deep within the muscles of the leg. Blood flows from the superficial veins into the deep venous system through small perforator veins. Superficial and perforator veins have one-way valves within them that allow blood to flow only in the direction of the heart when the veins are squeezed.

A blood clot (thrombus) in the deep venous system of the leg is not dangerous in itself. The situation becomes life-threatening when a piece of the blood clot breaks off (embolus, pleural=emboli), travels downstream through the heart into the pulmonary circulation system, and becomes lodged in the lung. Diagnosis and treatment of a deep venous thrombosis (DVT) is meant to prevent pulmonary embolism.

Clots in the superficial veins do not pose a danger of causing pulmonary emboli because the perforator vein valves act as a sieve to prevent clots from entering the deep venous system. They are usually not at risk of causing pulmonary embolism.

Picture of a blood clot is formed

What are the causes of deep vein thrombosis?

Blood is meant to flow; if it becomes stagnant there is a potential for it to clot. The blood in veins is constantly forming microscopic clots that are routinely broken down by the body. If the balance of clot formation and resolution is altered, significant clotting can occur. A thrombus can form if one, or a combination of the following situations is present.

Immobility

• Prolonged travel and sitting, such as long airplane flights ("economy class syndrome"), car, or train travel
  
  
• Hospitalization
  
  
• Surgery
  
  
• Trauma to the lower leg with or without surgery or casting
  
  
• Pregnancy, including 6-8 weeks post partum
  
  
• Obesity

Hypercoagulability (coagulation of blood faster than usual)

• Medications (for example, birth control pills, estrogen)
  
  
• Smoking
  
  
• Genetic predisposition
  
  
• Polycythemia (increased number of red blood cells)
  
  
• Cancer

Trauma to the vein

• Fracture to the leg
  
  
• Bruised leg
  
  
• Complication of an invasive procedure of the vein

What are the symptoms of deep vein thrombosis?

Superficial thrombophlebitis

Blood clots in the superficial vein system most often occur due to trauma to the vein which causes a small blood clot to form. Inflammation of the vein and surrounding skin causes the symptoms of any other type of inflammation including:

• redness,
  
  
• warmth,
  
  
• tenderness, and
  
  
• swelling.

Often the affected vein can be palpated (felt) as a firm, thickened cord. There may be inflammation that follows the course of part of the vein.

Although there is inflammation, there is no infection.

Varicosities can predispose to superficial thrombophlebitis. When the valves of the larger veins in the superficial system fail (the greater and lesser saphenous veins), blood can back up and cause the veins to swell and become distorted or tortuous. The valves fail when veins lose their elasticity and stretch. This can be due to age, prolonged standing, obesity, pregnancy, and genetic factors.

Deep Venous Thrombosis

The symptoms of deep vein thrombosis are related to obstruction of blood returning to the heart and causing a backup of blood in the leg. Classically, they symptoms include:

• pain,
  
  
• swelling,
  
  
• warmth, and
  
  
• redness.

Not all of these symptoms have to occur; one, all, or none may be present with a deep vein thrombosis. The symptoms may mimic an infection or cellulitis of the leg.

Historically, healthcare providers would try to elicit a couple of clinical findings to make a diagnosis. Dorsiflexion of the foot (pulling the toes towards the nose, or Homans' sign) and Pratt's sign (squeezing the calf to produce pain), have not been found effective in making a diagnosis.

When should I seek medical care for deep vein thrombosis?

The diagnosis of a superficial or deep thrombosis often relies on the clinical skill of the health care practitioner. Diagnostic tests need to be tailored to each situation.

Leg swelling, redness, and pain may be indicators of a blood clot and should not be ignored. These symptoms may be due to other causes (for example, cellulitis or infection), but it may be difficult to make the diagnosis without seeking medical advice.

If there is associated chest pain or shortness of breath, then further concern exists that a pulmonary embolus may be the cause. Once again, seeking immediate advice is appropriate.

How is deep vein thrombosis diagnosed?

The diagnosis of superficial thrombophlebitis is made clinically.

Ultrasound is now the standard method of diagnosing the presence of a deep vein thrombosis. The ultrasound technician may be able to determine whether a clot exists, where it is located in the leg, and how large it is. Ultrasounds can be compared over time to see whether a clot has grown or resolved. Ultrasound is better at "seeing" veins above the knee as compared to the veins below it.

Venography, injecting dye into the veins to look for a thrombus, is not usually performed any more and has become more of a historical footnote.

D-dimer is a blood test that may be used as a screening test to determine if a blood clot exists. D-dimer is a chemical that is produced when a blood clot in the body gradually dissolves. The test is used as a positive or negative indicator. If the result is negative, then no blood clot exists. If the D-dimer test is positive, it does not necessarily mean that a deep vein thrombosis is present since many situations will have an expected positive result (for example, from surgery, a fall, or pregnancy). For that reason, D-dimer testing must be used selectively.

Other blood testing may be considered based on the potential cause for the deep vein thrombosis.

What is the treatment for deep vein thrombosis?

Superficial Thrombophlebitis

Treatment for superficial blood clots is symptomatic with:

• warm compresses,
  
  
• leg compression, and
  
  
• an anti-inflammatory medications such as ibuprofen.

If the thrombophlebitis occurs near the groin where the superficial and deep systems join together, there is potential that the thrombus could extend into the deep venous system. These patients may require anticoagulation or blood thinning therapy (see below).

Deep venous thromboses

Deep venous thromboses that occur below the knee tend not to embolize (break loose). They may be observed with serial ultrasounds to make certain they are not extending above the knee. At the same time, the cause of the deep vein thrombosis may need to be addressed.

The treatment for deep venous thrombosis above the knee is anticoagulation, unless a contraindication exists. Contraindications include recent major surgery (since anticoagulation would thin all the blood in the body, not just that in the leg, leading to significant bleeding issues), or abnormal reactions when previously exposed to blood thinner medications.

Anticoagulation prevents further growth of the blood clot and prevents it from forming an embolus that can travel to the lung.

Anticoagulation is a two step process. Warfarin (Coumadin) is the drug of choice for anti-coagulation. It is begun immediately, but unfortunately it may take a week or more for the blood to be appropriately thinned. Therefore, low molecular weight heparin [enoxaparin (Lovenox)] is administered at the same time. It thins the blood via a different mechanism and is used as a bridge therapy until the warfarin has reached its therapeutic level. Enoxaparin injections can be given on an outpatient basis.

For those patients who have contraindications to the use of enoxaparin (for example, kidney failure does not allow the drug to be metabolized), intravenous heparin can be used as the first step. This requires admission to the hospital.

The dosage of warfarin is monitored by blood tests measuring the prothrombin time or INR (international normalized ratio). For an uncomplicated deep vein thrombosis, the recommended length of therapy with warfarin is three to six months.

Some patients may have contraindications for warfarin therapy, for example a patient with bleeding in the brain, major trauma, or recent significant surgery. An alternative may be to place a filter in the inferior vena cava (the major vein that collects blood from both legs) to prevent emboli from reaching the heart and lungs. These filters may be effective but also may be the source of new clot formation.

What are the complications of deep vein thrombosis?

Pulmonary embolism is the major complication of deep vein thrombosis. It can present with chest pain and shortness of breath and is a life-threatening condition. More than 90% of pulmonary emboli arise from the legs.

Post-phlebitic syndrome can occur after a deep vein thrombosis. The affected leg can become chronically swollen and painful with skin color changes and ulcer formation around the foot and ankle.

Can deep vein thrombosis be prevented?

As is the case with most medical illnesses, prevention is of prime importance. Minimizing risk factors is key to deep vein thrombosis prevention.

In the hospital setting, the staff works hard to minimize the potential for clot formation in immobilized patients. Compression stockings are routinely used. Surgery patients are out of bed walking (ambulatory) earlier and low dose heparin or enoxaparin is being used for deep vein thrombosis prophylaxis (measures taken to prevent DVT).

For those who travel, it is recommended that they get up and walk every couple of hours during a long trip.

Compression stockings may be helpful in preventing future deep vein thrombosis formation in patients with a previous history of a clot.

Fauci, Anthony S., et al. Harrison's Principles of Internal Medicine. 17th ed. United States: McGraw-Hill Professional, 2008.

sourceLast Editorial Review: 2/1/2010

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