Venous Thromboembolism Flashcards
What is an embolism?
A clot that breaks off and travels through circulation until it obstructs vessels of smaller diameter.
Describe venous thrombi
Also known as red clots, these consist of red cells encircled by a fibrin mesh
Describe arterial thrombi
These are also known as white clots, and these consist of platelets encircled by fibrin.
What is venous thromboembolism?
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)
What are the three main causes of venous thromboembolism (Virchow’s triad)?
> Blood stasis (pooling)
Disorder/dysfunction of vessel wall
Hypercoaguability (extra ‘sticky’ platelets)
What is the role of protein C in coagulation?
To inactivate factor Va and VIIIa (to inhibit thrombin formation and intrinsic ten-ase complex)
What is the role of protein S in coagulation?
It acts as a cofactor protein C to inactivate Va and VIIIa
What is the role of antithrombin in coagulation?
Inactivates thrombin (IIa) and factor Xa
What are some of the genetic risk factors associated with the development of venous thromboembolism?
Factor V Leiden, prothrombin gene mutation, protein C deficiency, protein S deficiency, antithrombin deficiency
What are some of the acquired risk factors for the development of venous thromboembolism?
Increasing age, cancer, antiphospholipid syndrome, infection, inflammatory disorders, nephrotic syndrome, obesity and smoking, inactivity
What is antiphospholipid syndrome?
An acquired form of thrombophilia that can be primary or secondary to connective tissue disorders
What is the difference between unfractionated heparin (UH) and low molecular weight heparin (LMWH)?
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.
How does heparin act as an anticoagulant?
It inhibits the action of factor Xa (which usually cleaves prothrombin to form thrombin)
What are the potential side-effects of heparin use?
Major bleeding, heparin-induced thrombocytopenia (which can increase risk of thrombosis) and osteoporosis with prolonged exposure
How do apixaban, edoxaban and rivaroxaban function as anticoagulants?
They inhibit factor Xa
Which coagulation factors require vitamin K to function?
Factor II (prothrombin), VII (part of extrinsic ten-ase), IX (part of intrinsic ten-ase) and factor X
How does dabigatran act as an anti-coagulant?
It inhibits thrombin
Outline the treatment for venous thromboembolism
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.
Describe how warfarin acts as an anticoagulant
It is a vitamin K antagonist and therefore it inhibits factors II, VII, IX and X as well as protein C and S
How is VTE treated in pregnancy?
LMWH is given; warfarin and DOACs (direct oral anticoagulants) can cross the placenta and have unprecedented defects on the foetus so are contraindicated
How is VTE treated if the patient is breastfeeding?
LMWH and warfarin may be used but not DOACs
What is a distal deep vein thrombosis?
When the thrombosis is confined to the veins below the popliteal vein (in the calf)
What is a proximal deep vein thrombosis?
Thrombosis that involves the popliteal vein or above
What are the signs and symptoms of deep vein thrombosis?
Pain, erythema, tenderness, swelling, warmth, ipsilateral oedema, superficial venous dilation
What test can be used to gauge probability of having VTE?
Wells score
Why would a D-dimer test be conducted in suspected VTE?
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
How is DVT diagnosed?
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
What complications may occur as a result of DVT?
Pulmonary embolism, clot extension, recurrent VTE and post-thrombotic syndrome
What is post-thrombotic syndrome?
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.
What are the signs and symptoms of pulmonary embolism?
Symptoms: breathlessness, pleuritic chest pain, haemoptysis, syncope, shock or hypotension
Signs: tachypnoea, tachycardia, crepitations (due to pulmonary oedema) and pleural rub
How may pulmonary embolism appear on ECG?
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
