Overview of Venous Thrombosis

  • Introduction

Thrombosis, or blood clotting, is a natural protective mechanism that prevents excessive bleeding when the body is injured. However, clotting becomes a problem when it obstructs blood flow. Clotting can occur in deep and superficial veins. Deep veins lie within muscles or body cavities, whereas superficial veins lie beneath the skin in the fat layer. Superficial veins connect with deep veins via ‘perforating veins’.

 

What is deep vein thrombosis?

Sydney Skin and Vein Clinic tells that Deep vein thrombosis (DVT) is the development of a blood clot in a deep vein. Although the deep veins of the legs are most commonly affected, a DVT can also affect the deep veins of the arms, pelvis or abdomen.

When clots form in superficial veins, this is called superficial venous thrombosis (SVT). If SVT leads to inflammation of the adjacent skin and fat, red tender lumps develop. This is called superficial thrombophlebitis (STP), or simply ‘phlebitis’.

While blood clots in superficial veins rarely cause serious problems, DVT requires immediate medical evaluation. Prompt treatment of DVT is vital to minimise immediate or long-term complications.

DVT can damage the affected deep vein, leading to chronic pain, swelling and skin changes of the affected limb. This is called post-thrombotic syndrome. DVT can also interfere with the return of blood to the heart, and result in swelling, painand inflammation of the affected limb. If part of the blood clot breaks off and travels to the lungs, it creates a condition called pulmonary embolism (PE), which may be life threatening. Signs of PE can include chest pain, palpitations, shortness of breath, coughing (with or without blood) and even sudden death.

Signs and symptoms

Symptoms of DVT can include swelling, tenderness and sometimes warmth of the affected limb. However, up to 50 per cent of patients with a DVT show no symptoms. These are called ‘silent’ or ‘asymptomatic’ DVT's. Silent DVTs may resolve by themselves, or can lead to complications such as PE.

Other conditions may present with similar symptoms to a DVT. These include soft tissue injury (muscle strain), inflammation of superficial veins (phlebitis), infection (cellulitis), skin inflammation (dermatitis) or a ruptured cyst behind the knee (ruptured Baker’s cyst).


What causes DVT?

Many external factors contribute to the formation of a DVT. One of the most common risk factors is immobility caused by long distance travel or hospitalisation. Some people are naturally predisposed to DVT because of an inherited tendency to clotting.

Several risk factors need to be present for a DVT to develop. An example is a female who is taking an oral contraceptive (risk factor 1) who has a sprained ankle (risk factor 2), is travelling from Sydney to New York in a plane (risk factor 3) and carries an inherited tendency to clotting (risk factor 4).


DVT Risk Factors

Reduced mobility
Contraction of the calf muscles during walking results in blood flow in the veins towards the heart. With immobility, blood flow becomes sluggish and the blood is more likely to clot. This leads to an increased risk of DVT. Patients over 60 are generally at greater risk, although patients of any age with reduced mobility (such as during long distance travel, or through illness or hospitalisation) can be affected.

Long distance travel with prolonged sitting
‘Long distance’ is defined as any trip of more than five hours. This includes car, coach and plane travel. In addition, the lower oxygen levels and humidity in an aeroplane cabin may further increase the risk of blood clots in the lower leg.

Injuries
Blood vessels may be damaged through trauma to the leg. Examples of such injuries include physical trauma, surgery or radiation therapy for cancer. Traumatic injuries damage the inner lining of veins, which can then trigger clot formation.

Obesity
Obesity is a known risk factor for cardiovascular diseases (strokes and heart attacks). Obesity is usually associated with reduced mobility, which adds to the DVT risk.

Pregnancy
Pregnancy increases the risk of DVT by several-fold. Most cases occur in the third trimester and immediately following delivery.

Oral contraceptives and hormone replacement therapy (HRT)
Hormonal preparations such as oral contraceptive pills or HRT increase the risk of clotting, particularly when combined with other risk factors like smoking, high blood pressure, obesity and inherited clotting disorders. Patients with a history of DVT should not take these preparations.


Cancer and other medical illnesses
Cancers may increase the blood’s tendency to clot. Cancers of the ovaries, pancreas, lymphatic system, liver, stomach, and colon are particularly likely to provoke DVT. Infections and medical conditions such as systemic lupus erythematosus (SLE), Crohn’s disease, rheumatoid arthritis, and glomerulonephritis may also stimulate the blood clotting process and promote DVT.

Inherited clotting disorders (Thromobophilia)
If blood clots occur in more than one person in a family, there may be an inherited clotting disorder. Genetic mutations can cause defective blood clotting factors. Factor V (five) Leiden and the prothrombin gene mutations are among the most commonly encountered gene mutations in the community. Individuals who inherit one of these mutations from either parent (heterozygous) may experience recurrent episodes of DVT, but the risk is highest if both parents were affected (homozygous).
Other inherited causes include deficiencies of certain blood components (antithrombin, protein C, and protein S) that ordinarily help dissolve blood clots. Some genetic mutations can lead to increased amounts of homocysteine in the circulation. Homocysteine is a compound that increases the tendency for the blood to clot, as well increasing the risk of stroke and heart attack.

Smoking
The role of smoking is controversial. In principle, smoking reduces the amount of oxygen in the blood stream and may damage vessel walls, potentially leading to clot formation.

How to reduce the risk of DVT

  • If you are scheduled for surgery or other procedures, notify your doctor if you have suffered from a blood clot in the past
  • If driving long distances, break up the trip with frequent rest stops every two hours to walk around
  • If you are on a plane, perform calf stretching exercises atregular intervals and walk around when you can
  • Avoid sitting still for long periods. When watching TV or reading, get up and move around once an hour
  • When sitting, perform heel/toe lifts frequently. This causes the calf muscle to contract and move the blood in your veins, making it less likely to clot
  • If at risk, drink plenty of fluids, but avoid alcohol, coffee and tea, which can contribute to dehydration and increase the risk of clotting
  • If you have an inherited risk of clotting, do not use birth control pills
  • There are blood tests available to determine if you have an inherited problem. If there is a history of DVT in your family, discuss this with your doctor
  • If you have had a DVT in the past, are pregnant, or have varicose veins, it may be helpful to wear compression stockings. Discuss this with your doctor
  • Do not smoke


Long-term consequences of DVT & PE

Very early in the development of a DVT, the body actually produces blood factors that help dissolve the clot. If the clot is in a superficial vein of the leg, or even in a calf vein, the clot frequently will dissolve totally. However, almost 90 per cent of patients with a large DVT in the thigh or groin will be left with some abnormality in the deep veins, even after adequate treatment.

In about 25 per cent of cases, DVT damages the affected vein and leads to long-lasting post-thrombotic syndrome(PTS). This presents as brownish discoloration of the skin, itching, swelling, slow-healing sores and pain. The affected skin becomes scarred and fragile, and can easily break down into an ulcer. It can also increase the risk of additional blood clots.

PTS almost always occurs within two years of the initial diagnosis of DVT. The damage may be partially prevented, however, if the patient wears graduated compression stockings as part of their long-term care for DVT.

A small number of patients suffer from recurrent pulmonary emboli, which can lead to high blood pressure in the lungs. This condition, in turn, can cause problems with the functioning of the heart and may require further medical or surgical treatment.

At a Glance

Deep vein thrombosis (DVT) is a serious medical condition with potential long term undesirable consequences.

Many risk factors increase the likelihood of DVT such as prolonged immobility, hormonal supplements, surgical operations, long distance tfravel, cancers and a number of inherited conditions.

Duplex Ultrasound is a non-invasive and simple way to diagnose DVT.

DVT is treated with heparin injections and some patients may require long term treatment with warfarin.

Phlebologists can diagnose and manage DVT and its long term complications such as post-thrombortic syndrome.

 

Contact Sydney Skin and Vein Clinic today for more information

 

Related Links:

Diagnosing DVT

Testing for Clotting Tendencies

Treatment