Venous Thromboembolism

Original Author: Mike Bath
Last Updated: April 21, 2017
Revisions: 36

Venous thromboembolism (VTE) is a term used to describe both deep vein thrombosis (DVT) and pulmonary embolism (PE) – disorders caused by thrombus formation.

VTE is one of the leading causes of preventable death in hospitals and is a important topic for juniors doctors to understand. All patients being admitted to the hospital or undergoing surgery should be assessed for VTE risk on admission and re-assessed within 24 hours or if a change occurs in the clinical situation.


Pathophysiology

The formation of a thrombus in a patient is dependent on any one of Virchow’s Triad being present:

  • Abnormal blood flow – usually due to recent immobility, such as a long-distance flight or being bed-bound in hospital. This is the most common underlying cause of a DVT.
  • Abnormal blood components – can be caused by multiple factors, such as smoking, sepsis, malignancy, or even inherited blood disorders (e.g. Factor V Leiden)
  • Abnormal vessel wall – can be from atheroma formation, inflammatory response, or direct trauma.
Fig 1 - Virchow's triad; factors that can predispose an individual to thrombosis.

Fig 1 – Virchow’s triad; factors that can predispose an individual to thrombosis.


Risk Factors

The main risk factors for developing a venous thromboembolism include:

  • Increasing age
  • Previous VTE
  • Smoking
  • Pregnancy or post-partum
  • Recent surgery (especially abdominal surgery, pelvic surgery, or hip or knee replacements)
  • Prolonged immobility (> 3 days)
  • Hormone replacement therapy or the combined oral contraceptive pill
  • Current active malignancy
  • Obesity
  • Known thrombophilia disorder (e.g. antiphospholipid syndrome or Factor V Leidin)

Deep Vein Thrombosis

A deep vein thrombosis refers to the formation of a blood clot in the deep veins of limbs, most commonly affecting those of the legs or pelvis.

Clinical Features

The most common presenting symptom of a DVT is unilateral leg pain and swelling. Other symptoms include pyrexia, pitting oedema, tenderness or prominent superficial veins. Importantly, 65% of DVTs are asymptomatic.

Fig 2 - Deep vein thrombosis in the right leg. The leg is swollen and red.

Fig 2 – Deep vein thrombosis in the right leg. The leg is swollen and red.

Investigations

If a deep vein thrombosis is suspected in a patient, the DVT Wells’ Score should be calculated:

  • Score less than or equal to 1 – DVT is clinically unlikely, requires a further D-dimer test to exclude*
  • Score greater than 1 – DVT is clinically likely and a DVT diagnosis should be confirmed via either a ultrasound scan (more common) or a contrast venography (rarely used)

*A D-dimer test is sensitive but not specific; a D-dimer may also be raised following recent surgery or trauma, with ongoing infection or inflammation, concurrent liver disease, or pregnancy, and indeed in any patient with a prolonged hospital stay.

Management

Any confirmed DVT should be treated with a therapeutic dose of LMWH (according to the patient’s body weight), with warfarin started concurrently.

LMWH is normally stopped after 5 days, assuming the INR has reached therapeutic values (between 2-3). Warfarin is continued for 6 months if no underlying cause is found, otherwise this can be kept as lifelone. Novel Oral Anticoagulants (NOACs) may be used in some centres, instead of warfarin.


Pulmonary Embolism

A pulmonary embolism (PE) refers to a blockage of the pulmonary artery by a substance that has travelled there in the bloodstream. Most commonly, this blockage is a deep vein thrombosis that has broken off and migrated. Other causes include a right-sided mural thrombus (e.g. post-MI), AF, neoplastic cells, or from fat cells (e.g. following tibial fracture).

Clinical Features

The key clinical features of a PE are sudden onset dyspnoea, pleuritic chest pain, cough, or rarely haemoptysis. Clinically, a patient may have tachycardia, tachypnoea, pyrexia, a raised JVP (rare), or pleural rub or pleural effusion (rare). Remember to examine for any signs of DVT in any patient with suspected PE.

Investigation

If pulmonary embolism is suspected in a patient, the PE Wells’ Score should be calculated:

  • Score less than or equal to 4 – PE clinically unlikely, requires a further D-dimer test to exclude*
  • Score greater than 4 –  PE clinically likely and a PE diagnosis should be confirmed with a CT Pulmonary Angiography (CTPA) scan (or V/Q scan in those with poor renal function).

*A D-dimer test is sensitive but not specific; a D-dimer may also be raised following recent surgery or trauma, with ongoing infection or inflammation, concurrent liver disease, or pregnancy, and indeed in any patient with a prolonged hospital stay.

An ECG should be performed due to the differential diagnosis of MI, however this most commonly shows no abnormalities or a sinus tachycardia. Less commonly, a PE may present on ECG with a right bundle branch block (RBBB), RV strain (inverted T waves in V1-Vand / or leads AvF-III), or a rare S1Q3T3 (deep S wave in Lead I, pathological Q wave in Lead III, and inverted T wave in Lead III)

NICE guidance suggests that any PE that is detected without any predisposing factors, that are recurrent, or with a positive family history requires cancer screening and clotting tests.

Fig 3 - CTPA scan showing a large pulmonary embolism at the bifurcation of the pulmonary artery

Fig 3 – CTPA scan showing a large pulmonary embolism at the bifurcation of the pulmonary artery

Management

The management of PE is the same as for a DVT, treating with a therapeutic dose of LMWH (according to the patient’s body weight) and start warfarin concurrently.


Thromboprophylaxis

An important part of the management of VTE is prophylaxis. There are two main methods of thromboprophylaxis used in hospital:

Mechanical Thromboprophylaxis

  • Antiembolic stockings (AES)
  • Intermittent pneumatic compression (IPC, more commonly used in theatre)

Pharmacological Thromboprophylaxis

  • Low molecular weight heparin (LMWH), unless poor renal function (eGFR<30) then consider unfractionated heparin (UFH)

All patients undergoing surgery should be offered mechanical prophylaxis unless otherwise contraindicated; mechanical prophylaxis (antiembolic stockings) should not be used in patients with peripheral arterial disease, peripheral oedema, local skin conditions, leg deformity, sensory impairment, or recent DVT.

Prophylaxis is typically continued until the patient is no longer considered to be at significant risk of VTE.

Key Points

  • VTE is a large cause of preventable death
  • VTE risk assessment should be done on all patients
  • Patients at risk of VTE should be commenced on appropriate thromboprophylaxis
  • Patients with a confirmed VTE require prompt treatment with anticoagulants

Quiz

Question 1 / 6
Which of the following contributes to 'abnormal blood components' of Virchow's triad?

Quiz

Question 2 / 6
Which of these in NOT a risk factor for a VTE?

Quiz

Question 3 / 6
Which of the following is the most common presenting feature of a DVT?

Quiz

Question 4 / 6
Which medications are most commonly used in the treatment of DVT?

Quiz

Question 5 / 6
What does a PE Well's score >4 indicate?

Quiz

Question 6 / 6
Which of these is NOT a contraindication to mechanical thromboprophylaxis?

Results

Further Reading

Risk of symptomatic venous thromboembolism following emergency appendicectomy in adults
Humes DJ et al., British Journal of Surgery

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