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.

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

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

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.