Acute Clot

An acute clot – also referred to as DVT or 'Deep Vein Thrombosis', is where a blood clot (medical term - 'thrombus') forms in a deep vein in the body. Although the most common types of clots are in the legs, they can also occur in the arms, in the pelvic area or in the abdomen.

As opposed to chronic clot, which describes a known or previously diagnosed clot, the term 'acute clot' applies to the onset of symptoms within the last month.

How DVTs form

Blood clotting, referred to by the medical term 'thrombosis' is a natural reaction to prevent blood loss when the body is injured. However, if it occurs within normal veins it can block or slow blood flow which leads to reduced blood flow, swelling, pain and discoloration.

More seriously however, if the blood clot breaks away, it can travel through the veins to the lungs where it can cause a 'pulmonary embolism' or ‘PE’ which is a very serious condition that may lead to sudden death. Symptoms of pulmonary embolism include pain in the chest area, heart palpitations, shortness of breath and coughing.

Over time the blockage can cause chronic pain, as well as swelling, skin changes and ulceration to the affected area, a condition called 'post thrombotic syndrome'.

Causes of DVT

There are several risk factors that may put you at greater risk of developing an acute clot. These include...

Long periods of sitting or lying still

This risk factor affects those on long distance journeys (over five hours) most commonly on an aircraft, but also in cars, long distance buses etc. This also impacts older people who are less mobile than they used to be and who do not move or walk much, as well as people who are in a hospital bed for long periods.

Genetic predisposition to formation of acute clots (thromobophilia)

Certain gene mutations can cause either deficiencies or overproduction of blood components that make carriers more prone to blood clotting (as the blood is too thick). Two common gene mutations called Factor V Leiden and the prothrombin mutation make carriers of these genes more prone to acute clots, especially if both parents carry these genes.


Some types of injury can be a risk factor for acute clots, such as injuries to the legs where the lining of the veins can be damaged. Some medical treatments such as surgery and radiation therapy can also heighten the risk of developing acute clots.


Being overweight or obese is a known risk factor for acute clots as well as for other cardiovascular conditions such as heart attacks and stroke. It is clearly linked to the first risk factor listed here, especially where there is decreased mobility.


Being pregnant is a high-risk factor. During pregnancy, the blood becomes hypercoagulable (or too thick), there is slowed blood flow back from the legs due to the size of the baby and the mother is generally less physically active than normal. If acute clots form they generally do so in the third trimester or immediately after the baby is born.

Some illnesses

A number of different type of cancer are linked to an increased acute clot risk factor. These are liver cancer, stomach cancer and colon cancer (cancer of the bowel) as well as ovarian cancer, pancreatic cancer and cancer of the lymphatic system. Some other conditions, especially inflammatory bowel conditions such as Crohn's disease, have an increased risk of acute clots forming. Rheumatoid arthritis also increases the risk.

Some medication

Hormone based medications including Hormone Replacement Therapy and the contraceptive pill both increase the risk of acute clot formation.


Smoking is regarded as being a 'moderate' risk factor.


People over the age of 60 are at higher risk of developing acute clots.

In practice, it is the combination of one or more of these risk factors that increases the overall risk, for example someone who has recently undergone surgery and is obese taking a long-distance flight would be at very high risk of developing an acute clot during the flight.


One or more of a range of diagnostic tools may be used, including:

For acute clot/deep vein thrombosis:

  • Duplex Ultrasound (non-invasive)
  • MRI
  • CT angiogram (a 'cat scan')
  • Venography - an x-ray performed to track a special dye injected into the vein

For pulmonary embolism:

  • CT angiogram
  • Pulmonary angiography
  • Lung perfusion scans

Treatment Options


Most patients diagnosed with acute clot and/or pulmonary embolism will need to start treatment immediately. The blood is thinned with an “anticoagulant” such as Warfarin and Heparin are used to stop new clots from forming. New Oral Anticoagulants (NOACs) are often used as they don’t require blood tests, but again they have pros and cons which Dr Hagley can discuss with you.

Depending on the patient's specific circumstances, treatment may be over a short period of time or may be needed indefinitely.


If your clot is recent (less than 2 weeks old) and it is causing you significant pain and swelling there are treatments to dissolve the clot. This uses a much stronger clot “busting” medication (thrombolysis) rather than just “thinning” the blood. Because the medication is much stronger it needs to be delivered directly into the clot within the vein.

This is called catheter directed thrombolysis (CDT) and it is now widely accepted as the best treatment in suitable patients for acute DVT involving the groin and abdominal veins. It quickly restores venous flow and preserves venous valves which are normally damaged by the DVT.

One of the causes of large abdominal DVT’s is the presence of an underlying narrowing of the vein. After successful completion of clearing the vein, the narrowing can then be treated to prevent recurrence.

Catheter directed thrombolysis does carry risks and isn’t the best option for all patents, Dr Hagley will thoroughly discuss your options so that you can come to a clear decision together.

The Procedure

The procedure is referred to as thrombolysis or catheter directed thrombolysis (CDT) and is a procedure to re-open or improve the blood flow in blocked veins. It is carried out in a specific radiology suite and is performed under X-ray guidance. The procedure is generally performed under a local anaesthetic (the patient is awake, but experiences no pain).

In most cases this is performed as a ‘percutaneous’ procedure (no large cut and no stitches), where a thin tube called a catheter is inserted into the large vein in the groin (the femoral vein) and then manoeuvred over a guidewire through the various veins to the section where the narrowing/blockage is situated. The infusion of thrombolytic or “clot busting” medication will then commence. Dr Hagley uses different techniques depending on the circumstances, so the procedure usually takes about an hour, but some clots take time to dissolve and the infusion may run for up to 3 days.

If an underlying narrowing is identified after the clot is cleared a stent can be placed via the same catheter and incision (see section on balloons and stents). You may spend time in the intensive care unit (ICU). You will be given additional medication to ensure the clot dissolves, usually in 12-14 hours. A compression stocking or sleeve will be placed on your leg or arm.

Dr Hagley will likely recommend you take a blood thinner for at least 3-6 months.