In medicine, deep vein thrombosis (also known as deep-vein thrombosis or deep venous thrombosis and usually abbreviated as DVT) is the formation of a blood clot ("thrombus") in a deep vein. It is a form of thrombophlebitis (inflammation of a vein with clot formation).
Deep vein thrombosis 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 (if spontaneous, this is known as Paget-Schrötter disease). A DVT can occur without symptoms, but in many cases the affected extremity will be painful, swollen, red, warm and the superficial veins may be engorged. The greatest complication of a DVT is that the clot could dislodge and travel to the lungs, which is called a pulmonary embolism. A late complication of DVT is the post-phlebitic syndrome, which can manifest itself as edema, pain or discomfort and skin problems.
According to Virchow's triad, venous thrombosis occurs via three mechanisms: decreased flow rate of the blood, damage to the blood vessel wall and an increased tendency of the blood to clot (hypercoagulability). Several medical conditions can lead to DVT, such as compression of the veins, physical trauma, cancer, infections, certain inflammatory diseases and specific conditions such as stroke, heart failure or nephrotic syndrome. There are several factors which can increase a person's risk for DVT, including surgery, hospitalization, immobilization (such as when orthopedic casts are used, or during long-haul flights, leading to economy class syndrome), smoking, obesity, age, certain drugs (such as estrogen or erythropoietin) and inborn tendencies to form clots known as thrombophilia (for example, in carriers of factor V Leiden). Women have an increased risk during pregnancy and in the postnatal period.
The most commonly used tests for the diagnosis of DVT are a blood test called D-dimers and doppler ultrasound of the affected veins. Sometimes, further testing is required to find the cause of the DVT. In specific cases, an attempt can be made to break down the clot (using thrombolytic agents). To prevent further accrual and formation of new clots with a risk of pulmonary embolism, anticoagulation (blood thinners) is advised (if not possible, an inferior vena cava filter may be used). Prevention of DVT is advised in many medical and surgical inpatients using anticoagulants, graduated compression stockings (also known as thromboembolic deterrent stockings) or intermittent pneumatic compression devices.
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, intravenous drug use 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.
Virchow's triad is a group of three 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).
The most common risk factors are recent surgery or hospitalization. 40% of these patients did not receive heparin prophylaxis. Other risk factors include advanced age, obesity, infection, immobilization, 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. 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.
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.
Wells score or criteria: (Possible score -2 to 9)
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.
Since publication of the ACCP guidelines, an additional randomized controlled trial and meta-analysis 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 and an earlier trial are relevant yet inconclusive.
Chronic renal dialysis patients may be at increased risk of thromboembolism, but randomized controlled trials have not addressed the risk benefit of prophylaxis.
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.
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 comorbidities (e.g. malignancy).
Research conducted at University of Insubria, Research Center has updated our knowledge about thrombosis prevention.
Mar 11, 2010; Data detailed in 'Cerebral vein thrombosis' have been presented. "Advances in neuroimaging have modified our knowledge on...
Researchers from Maria Hospital, Neurology Department detail new studies and findings in the area of thrombosis risk factors.(Report)
Sep 25, 2008; New research, 'Hypothyroidism and cerebral vein thrombosis--a possible association,' is the subject of a report. "There are many...