Venous Thromboembolism Flashcards
What are the three components of Virchow’s Triad
- Abnormal blood flow - stasis
- Hypercoagulability
- Vascular Injury
Which factors of the coagulation cascade are important in the generation of thrombin
Factors 5 and 8
What does tissue damage lead to the release of
Tissue factor
What two factors combine to form factor 10a
Factors 7a and tissue factor
What is kind of membrane is required for the clotting cascade to occur
A phospholipid membrane in the form of platelets or monocytes.
What does the tissue factor pathway inhibitor do
Prevents the generation of factor 10a.
What is post thrombotic syndrome
A permanent pain and swelling.
What are the risk factors for venous thromboembolism
- Age
- Obesity
- Varicose veins
- Previous VTE
- Thombophilia
- Cancer
- Other thrombotic states
- Hormone therapy
- Pregnancy
- Immobility
- Hospitalisation
- Anaesthesia
- Central venous catheters.
What is the issue with diagnosis of VTE
80% of DVT are clinically silent.
What are the clinical symptoms of DVT
- Pain
- Swelling
- Increased temperature of the limb
- Dilatation of superficial veins
Is DVT usually unilateral or bilateral
Unilateral
When may a DVT be bilateral
If thrombosis is sited in the inferior vena cava
What are the differential diagnosis of DVT
Calf haematoma, ruptured Baker’s cyst, cellulitis
What is Well’s score used for
To predict which patients might have DVT. Patients are put into low, moderate and high risk categories depending on the score.
What investigations are used to diagnose DVT
- Contrast venography
- Venous ultrasoundography
- D-dimer test
What are the diagnostic results of DVT in venous ultrasoundography
Non-compressibility of the common femoral vein or popliteal vein.
What are the clinical features of pulmonary embolism
- Collapse, faintness, crushing central chest pain
- Pleuritic chest pain
- Difficulty breathing
- Haemoptysis
- Extertional dyspnoea
What is pleuritic chest pain
Pain in the chest which worsens when breathing in
What is haemoptysis
Coughing up blood
What investigations are used in the diagnosis of PE
- Chest x-ray
- Electrocardiogram
- Arterial blood gases
- D-dimer
- Ventilation perfusion scan
- CT angiogram
- Echocardiogram
Why is a chest x-ray used in the diagnosis of PE
To rule out other possible diagnosis
What will be shown on an echocardiogram in someone with a pulmonary embolism
On an echocardiogram, a high right sided ventricular pressure will be shown due to resistance from the pulmonary circulation as a result of the PE.
What are the principles of anticoagulant therapy
Rapid initial anticoagulation followed by extended therapy.
What can be given for rapid initial anticoagulation
Parenteral anticoagulant or direct oral anticoagulant
What are examples of parenteral anticoagulants
- Heparin
- Low molecular weight heparin
- Fondaparinux
When are direct oral anticoagulants used
In emergency situations.
Why are direct oral anticoagulants only used in emergency situations
Because it takes 4 hours for absorption so if a person has collapsed due to PE, they will be given parenteral heparin as this ensures absorption and brings about a response more quickly.
What can be given for extended therapy after a PE
An orally active anticoagulant or a direct anticoagulant.
What is an example of an orally active anticoagulant
A vitamin K antagonist such as warfarin.
What is the aim of extended anticoagulant therapy
To prevent recurrent thrombosis and chronic complications such as post phlebitic syndrome
What are DOACs
Direct oral anticoagulants
What are four examples of DOACs
Dabigatran, Rivaroxaban, Edoxaban and apixaban
What does dabigatran do
Dabigatran inhibits the action of thrombin in the formation of a thrombus
What do rivaroxaban, edoxaban and apixaban
Rivaroxaban, edoxaban and apixaban inhibit factor 10a to prevent the progression of the clotting cascade
Which two points are important in the clotting cascade and therefore are drug targets
The formation of factor 10a and thrombin action to convert fibrinogen into fibrin.
What is sometimes given alongside DOACs
Heparin
What is the action of DOACs
They enable rapid initial anticoagulation orally and then are given at a lower dose for secondary prevention of venothromboembolism.
Which DOACs do not need to be given alongside heparin
Apixaban and rivaroxaban
What investigations are used to investigate a procoagulant tendency
- Full blood count
- Antithrombin
- Protien C
- Protein S
- Thrombin time
In what situation is the DOAC argatroban used
Where the person is allergic to heparin.
What factors are thrombin and prothrombin
Thrombin is factor IIa and prothrombin is factor II.
What are two types of heparin
Unfractionated and low-molecular weight heparin.
Which type of heparin is more bioavailable
Low molecular weight heparin
How does heparin work
It binds to pentasaccharide on antithrombin and brings about its inhibitory action towards factor Xa and thrombin.
What’s negative about prescribing unfractionated heparin
It has an unpredictable anticoagulant response due to binding to plasma proteins so requires monitoring using APTT.
What conditions could develop due to unfractionated heparin
Osteoporosis and heparin-induced thrombocytopenia
What is there a high risk of with unfractionated heparin
Bleeding.
What are the two positives about the use of low molecular weight heparin
It has almost 100% bioavailability and no monitoring is required.
What is the negative about the use of low molecular weight heparin
It is not reversible
What are coumarins
They inhibit vitamin K dependent carboxylation of factors 2, 7, 9 and 10
What is the most common coumarin
Vitamin K
By what method are coumarins such as warfarin taken
Orally
How are coumarins such as warfarin monitored
By the international normalised ratio (INR) derived from the prothrombin time (PT)
How can the effect of warfarin be reversed
Dietary intake of vitamin K, fresh frozen plasma and concentrates of the factors inhibited by warfarin.
What are the negative aspects of prescribing warfarin
There are many drug interactions with warfarin and requires monitoring at least monthly.
What is the negative aspect about using DOACs instead of warfarin
Their effect cannot really be revered.
Which is currently the only DOAC that can be reversed
Dabigatran. The factor 10a inhibitors cannot yet be reversed.
