Deep vein thrombosis

This article is about Deep-vein thrombosis. For other uses of DVT, see DVT (disambiguation).

Deep-vein thrombosis (also known as deep-venous thrombosis or DVT and colloquially as economy class syndrome) is the formation of a blood clot ("thrombus") in a deep vein. It commonly affects the leg veins, such as the femoral vein or the popliteal vein or the deep veins of the pelvis. Occasionally the veins of the arm are affected (known as Paget-Schrötter disease). Thrombophlebitis is the more general class of pathologies of this kind. There is a significant risk of the thrombus embolizing and traveling to the lungs causing a pulmonary embolism.

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Signs and symptoms

There may be no symptoms referrable to the location of the DVT, but the classical symptoms of DVT include pain, swelling and redness of the leg and dilation of the surface veins. In up to 25% of all hospitalized patients, there may be some form of DVT, which often remains clinically inapparent (unless pulmonary embolism develops).

There are several techniques during physical examination to increase the detection of DVT, such as measuring the circumference of the affected and the contralateral limb at a fixed point (to objectivate edema), and palpating the venous tract, which is often tender. Physical examination is unreliable for excluding the diagnosis of deep vein thrombosis.

In phlegmasia alba dolens, the leg is pale and cool with a diminished arterial pulse due to spasm. It usually results from acute occlusion of the iliac and femoral veins due to DVT.

In phlegmasia cerulea dolens, there is an acute and nearly total venous occlusion of the entire extremity outflow, including the iliac and femoral veins. The leg is usually painful, cyanosed and oedematous. Venous gangrene may supervene.

It is vital that the possibility of pulmonary embolism be included in the history, as this may warrant further investigation (see pulmonary embolism).

A careful history has to be taken considering risk factors (see below), including the use of estrogen-containing methods of hormonal contraception, recent long-haul flying, and a history of miscarriage (which is a feature of several disorders that can also cause thrombosis). A family history can reveal a hereditary factor in the development of DVT.

Cause/Etiology

Main article: Thrombosis

Virchow's triad is a group of 3 factors known to affect clot formation: rate of flow, the consistency (thickness) of the blood, and qualities of the vessel wall. Virchow noted that more deep venous thrombosis occurred in the left leg than in the right and proposed compression of the left common iliac vein by the overlying right common iliac artery as the underlying cause (see May-Thurner syndrome).^[1]

The most common risk factors are recent surgery or hospitalization.^[2] 40% of these patients did not receive heparin prophylaxis. Other risk factors include advanced age, obesity, infection, immobilization, female sex, use of combined (estrogen-containing) forms of hormonal contraception, tobacco usage and air travel ("economy class syndrome", a combination of immobility and relative dehydration) are some of the better-known causes.^[3] Thrombophilia (tendency to develop thrombosis) often expresses itself with recurrent thromboses.

It is recognized that thrombi usually develop first in the calf veins, "growing" in the direction of flow of the vein. DVTs are distinguished as being above or below the popliteal vein. Very extensive DVTs can extend into the iliac veins or the inferior vena cava. The risk of pulmonary embolism is higher in the presence of more extensive clots.

Diagnosis

The gold standard is intravenous venography, which involves injecting a peripheral vein of the affected limb with a contrast agent and taking X-rays, to reveal whether the venous supply has been obstructed. Because of its invasiveness, this test is rarely performed.

Physical examination

1. Homan's test: Dorsiflexion of foot elicits pain in posterior calf. However, it must be noted that it is of little diagnostic value and is theoretically dangerous because of the possibility of dislodgement of loose clot.
2. Pratt's sign: Squeezing of posterior calf elicits pain.

However, these medical signs do not perform well and are not included in clinical prediction rules that combine best findings in order to diagnose DVT.^[4]

Probability scoring

In 2006, Scarvelis and Wells overviewed a set of clinical prediction rules for DVT,^[5] on the heels of a widely adopted set of clinical criteria for pulmonary embolism.^[6][7]

Wells score or criteria: (Possible score -2 to 9)

1) Active cancer (treatment within last 6 months or palliative) -- 1 point

2) Calf swelling >3 cm compared to other calf (measured 10 cm below tibial tuberosity) -- 1 point

3) Collateral superficial veins (non-varicose) -- 1 point

4) Pitting edema (confined to symptomatic leg) -- 1 point

5) Swelling of entire leg - 1 point

6) Localized pain along distribution of deep venous system -- 1 point

7) Paralysis, paresis, or recent cast immobilization of lower extremities -- 1 point

8) Recently bedridden > 3 days, or major surgery requiring regional or general anesthetic in past 12 weeks -- 1 point

9) Previously documented DVT -- 1 point

10) Alternative diagnosis at least as likely -- Subtract 2 points

Interpretation:

Score of 2 or higher - deep vein thrombosis is likely. Consider imaging the leg veins.

Score of less than 2 - deep vein thrombosis is unlikely. Consider blood test such as d-dimer test to further rule out deep vein thrombosis.

Blood tests

D-dimer

Main article: d-dimer

In a low-probability situation, current practice is to commence investigations by testing for D-dimer levels. This cross-linked fibrin degradation product is an indication that thrombosis is occurring, and that the blood clot is being dissolved by plasmin. A low D-dimer level should prompt other possible diagnoses (such as a ruptured Baker's cyst, if the patient is at sufficiently low clinical probability of DVT.^[8][9]

Other blood tests

Other blood tests usually performed at this point are^{[citation needed]}:

• complete blood count
• Primary coagulation studies: PT, APTT, Fibrinogen
• liver enzymes
• renal function and electrolytes

Imaging the leg veins

Impedance plethysmography, Doppler ultrasonography, compression ultrasound scanning of the leg veins, combined with duplex measurements (to determine blood flow), can reveal a blood clot and its extent (i.e. whether it is below or above the knee). Duplex Ultrasonography,due to its high sensitivity, specificity and reproducibility, has replaced venography as the most widely used test in the evaluation of the disease. This test involves both a B mode image and Doppler flow analysis.

Therapy

Hospitalization

Treatment at home is an option according to a meta-analysis by the Cochrane Collaboration.^[10] Hospitalization should be considered in patients with more than two of the following risk factors as these patients may have more risk of complications during treatment^[11]:

• bilateral DVT, renal insufficiency, body weight <70 kg, recent immobility, chronic heart failure, and cancer

Anticoagulation

Main article: Anticoagulation

Anticoagulation is the usual treatment for DVT. In general, patients are initiated on a brief course (i.e., less than a week) of heparin treatment while they start on a 3- to 6-month course of warfarin (or related vitamin K inhibitors). Low molecular weight heparin (LMWH) is preferred,^[12] though unfractionated heparin is given in patients who have a contraindication to LMWH (e.g., renal failure or imminent need for invasive procedure). In patients who have had recurrent DVTs (two or more), anticoagulation is generally "life-long." The Cochrane Collaboration has meta-analyzed the risk and benefits of prolonged anti-coagulation.^[13]

An abnormal D-dimer level at the end of treatment might signal the need for continued treatment among patients with a first unprovoked proximal deep-vein thrombosis.^[14]

Thrombolysis

Main article: Thrombolysis

Thrombolysis is generally reserved for extensive clot, e.g. an iliofemoral thrombosis. Although a meta-analysis of randomized controlled trials by the Cochrane Collaboration shows improved outcomes with thrombolysis,^[15] there may be an increase in serious bleeding complications.

Compression stockings

Elastic compression stockings should be routinely applied "beginning within 1 month of diagnosis of proximal DVT and continuing for a minimum of 1 year after diagnosis".^[12] Starting within one week may be more effective.^[16] The stockings in almost all trials were stronger than routine anti-embolism stockings and created either 20-30 mm Hg or 30-40 mm Hg. Most trials used knee-high stockings. A meta-analysis of randomized controlled trials by the Cochrane Collaboration showed reduced incidence of post-phlebitic syndrome.^[17] The number needed to treat is quite potent at 4 to 5 patients need to prevent one case of post-phlebitic syndrome.^[18]

Inferior vena cava filter

Main article: Inferior vena cava filter

Inferior vena cava filter reduces pulmonary embolism^[19] and is an option for patients with an absolute contraindiciation to anticoagulant treatment (e.g., cerebral hemorrhage) or those rare patients who have objectively documented recurrent PEs while on anticoagulation, an inferior vena cava filter (also referred to as a Greenfield filter) may prevent pulmonary embolisation of the leg clot. However these filters are themselves potential foci of thrombosis,^[20] IVC filters are viewed as a temporizing measure for preventing life-threatening pulmonary embolism.^[21]

Prognosis

Post-phlebitic syndrome occurs in 10% of patients with deep vein thrombosis (DVT). It presents with leg oedema, pain, nocturnal cramping, venous claudication, skin pigmentation, dermatitis and ulceration (usually on the medial aspect of the lower leg).

Prophylaxis (Prevention)

Clinical practice guidelines by the American College of Chest Physicians (ACCP) provide recommendations on DVT prophylaxis in hospitalized patients ^[22].

General Medical Inpatients

Regarding general medical inpatients the guidelines state, "In acutely ill medical patients who have been admitted to the hospital with congestive heart failure or severe respiratory disease, or who are confined to bed and have one or more additional risk factors, including active cancer, previous VTE, sepsis, acute neurologic disease, or inflammatory bowel disease, we recommend prophylaxis with LDUH (Grade 1A) or LMWH (Grade 1A)^[22]." Enoxaparin or unfractionated heparin may be used.^[23] LMWH may be more effective than UFH. If UFH heparin is used, 5000 U 3 times daily may be more effective.^[24]

Since publication of the ACCP guidelines, an additional randomized controlled trial ^[25] and meta-analysis ^[26] including the trial have been published. The meta-analysis concluded " Anticoagulant prophylaxis is effective in preventing symptomatic venous thromboembolism during anticoagulant prophylaxis in at-risk hospitalized medical patients. Additional research is needed to determine the risk for venous thromboembolism in these patients after prophylaxis has been stopped." With regards to which patients are at risk, most studies in the meta-analysis were of patients with New York Heart Association Functional Classification (NYHA) III-IV heart failure. Regarding patients at lesser risk of DVT, the trial above^[25] and an earlier trial^[27] are relevant yet inconclusive.

Chronic renal dialysis patients may be at increased risk of thromboembolism^[28], but randomized controlled trials have not addressed the risk benefit of prophylaxis.

Surgery Patients

In patients who have undergone surgery, low molecular weight heparins (LMWH) are routinely administered to prevent thrombosis. LMWH can only currently be administered subcutaneously by injection. Prophylaxis for pregnant women who have a history of thrombosis may be limited to LMWH injections or may not be necessary if their risk factors are mainly temporary.

Early and regular ambulation (walking) is a treatment that predates anticoagulants and is still recognized and used today. Walking activates the body's muscle pumps, increasing venous velocity and preventing stasis. Intermittent pneumatic compression (IPC) machines have proven protective in bed- or chair-ridden patients at very high risk or with contraindications to heparins. IPC machines use air bladders that are wrapped around the thigh and/or calf. The bladders alternately inflate and deflate, squeezing the muscles and increasing blood velocity by as much as 500%. IPC machines have been proven effective on knee and hip surgery patients (a population with a risk as high as 80% with no prophylactic treatment) of developing DVT and PE. Alternatively, between 150-300mg of aspirin can be taken.

Travelers

Main article: Economy class syndrome

There is clinical evidence to suggest that wearing compression socks while travelling also reduces the incidence of thrombosis in people on long haul flights. A randomised study in 2001 compared two sets of long haul airline passengers, one set wore travel compression hosiery the others did not. The passengers were all scanned and blood tested to check for the incidence of DVT. The results showed that asymptomatic DVT occurred in 10% of the passengers who did not wear compression socks. The group wearing compression had no DVTs. The authors concluded that wearing elastic compression hosiery reduces the incidence of DVT in long haul airline passengers. ^[29].

Epidemiology

DVTs occur in about 1 per 1000 persons per year. About 1-5% will die from the complications (i.e. pulmonary embolism).

DVT is much less common in the pediatric population. About 1 in 100,000 people under the age of 18 experiences deep vein thrombosis, possibly due to a child's high rate of heartbeats per minute, relatively active lifestyle when compared with adults, and fewer comorbodities (e.g. malignancy).

See also

• Venogram (medical)

References