Venous Thromboembolism

Question 1

What is an embolism?

Answer 1

A clot that breaks off and travels through circulation until it obstructs vessels of smaller diameter.

Question 2

Describe venous thrombi

Answer 2

Also known as red clots, these consist of red cells encircled by a fibrin mesh

Question 3

Describe arterial thrombi

Answer 3

These are also known as white clots, and these consist of platelets encircled by fibrin.

Question 4

What is venous thromboembolism?

Answer 4

A general term for a variety of conditions including:
> Deep vein thrombosis
> Pulmonary embolism
> Other causes of embolism such as air, amniotic fluid and fat (uncommon)

Question 5

What are the three main causes of venous thromboembolism (Virchow’s triad)?

Answer 5

> Blood stasis (pooling)
Disorder/dysfunction of vessel wall
Hypercoaguability (extra ‘sticky’ platelets)

Question 6

What is the role of protein C in coagulation?

Answer 6

To inactivate factor Va and VIIIa (to inhibit thrombin formation and intrinsic ten-ase complex)

Question 7

What is the role of protein S in coagulation?

Answer 7

It acts as a cofactor protein C to inactivate Va and VIIIa

Question 8

What is the role of antithrombin in coagulation?

Answer 8

Inactivates thrombin (IIa) and factor Xa

Question 9

What are some of the genetic risk factors associated with the development of venous thromboembolism?

Answer 9

Factor V Leiden, prothrombin gene mutation, protein C deficiency, protein S deficiency, antithrombin deficiency

Question 10

What are some of the acquired risk factors for the development of venous thromboembolism?

Answer 10

Increasing age, cancer, antiphospholipid syndrome, infection, inflammatory disorders, nephrotic syndrome, obesity and smoking, inactivity

Question 11

What is antiphospholipid syndrome?

Answer 11

An acquired form of thrombophilia that can be primary or secondary to connective tissue disorders

Question 12

What is the difference between unfractionated heparin (UH) and low molecular weight heparin (LMWH)?

Answer 12

UH has an immediate onset of activity with a short half-life, whereas LMWH is as effective as UH but is also safer as it produces more predictable anticoagulant response with a longer half-life.

Question 13

How does heparin act as an anticoagulant?

Answer 13

It inhibits the action of factor Xa (which usually cleaves prothrombin to form thrombin)

Question 14

What are the potential side-effects of heparin use?

Answer 14

Major bleeding, heparin-induced thrombocytopenia (which can increase risk of thrombosis) and osteoporosis with prolonged exposure

Question 15

How do apixaban, edoxaban and rivaroxaban function as anticoagulants?

Answer 15

They inhibit factor Xa

Question 16

Which coagulation factors require vitamin K to function?

Answer 16

Factor II (prothrombin), VII (part of extrinsic ten-ase), IX (part of intrinsic ten-ase) and factor X

Question 17

How does dabigatran act as an anti-coagulant?

Answer 17

It inhibits thrombin

Question 18

Outline the treatment for venous thromboembolism

Answer 18

In acute situations IV UH heparin, subcutaneous LMWH and subcutaneous fondaparinux (all factor Xa inhibitors) are given. This is then followed by replacement of heparin with warfarin which is then monitored.

Question 19

Describe how warfarin acts as an anticoagulant

Answer 19

It is a vitamin K antagonist and therefore it inhibits factors II, VII, IX and X as well as protein C and S

Question 20

How is VTE treated in pregnancy?

Answer 20

LMWH is given; warfarin and DOACs (direct oral anticoagulants) can cross the placenta and have unprecedented defects on the foetus so are contraindicated

Question 21

How is VTE treated if the patient is breastfeeding?

Answer 21

LMWH and warfarin may be used but not DOACs

Question 22

What is a distal deep vein thrombosis?

Answer 22

When the thrombosis is confined to the veins below the popliteal vein (in the calf)

Question 23

What is a proximal deep vein thrombosis?

Answer 23

Thrombosis that involves the popliteal vein or above

Question 24

What are the signs and symptoms of deep vein thrombosis?

Answer 24

Pain, erythema, tenderness, swelling, warmth, ipsilateral oedema, superficial venous dilation

Question 25

What test can be used to gauge probability of having VTE?

Answer 25

Wells score

Question 26

Why would a D-dimer test be conducted in suspected VTE?

Answer 26

This is a blood test for a non-specific marker of fibrin breakdown breakdown which is usually raised in VTE, but also in cancer, infection, inflammation, post-operations and pregnancy, and therefore a positive result doesn’t confirm VTE

Question 27

How is DVT diagnosed?

Answer 27

Pre-test probability is conducted via the Well’s score, then a D-dimer test is conducted (elevated may indicate DVT as it’s due to increased fibrin breakdown), and then assess with compression ultrasound

Question 28

What complications may occur as a result of DVT?

Answer 28

Pulmonary embolism, clot extension, recurrent VTE and post-thrombotic syndrome

Question 29

What is post-thrombotic syndrome?

Answer 29

Involved recurrent pain and swelling in the affected leg which can progress to local skin pigmentation and ulceration. This occurs due to venous hypertension (due to obstruction or valvular damage), abnormal microcirculation (where blood flows from deep to superficial veins) and is far more common after proximal DVT.

Question 30

What are the signs and symptoms of pulmonary embolism?

Answer 30

Symptoms: breathlessness, pleuritic chest pain, haemoptysis, syncope, shock or hypotension

Signs: tachypnoea, tachycardia, crepitations (due to pulmonary oedema) and pleural rub

Question 31

How may pulmonary embolism appear on ECG?

Answer 31

Sinus tachycardia seen most commonly, but this may be accompanied by a S1Q3T3 wave:

> A large S wave on lead I
A visible Q wave in lead III
Inverted T wave in lead III