17.2 Venous thromboembolism and anticoagulants Flashcards
What does the term venous thromboembolism refer to?
Venous thromboembolism refers to deep vein thromboses and pulmonary emboli.
What are anticoagulants used to treat?
- DVT
- PE
- Atrial fibrillation (irregular synchrony of the atria which can lead to thrombi forming in the heart)
What score is used to determine a patient’s risk of a DVT?
Wells score
<2 = DVT unlikely
2 or greater = DVT likely
How is a DVT confirmed?
Using a venous doppler ultrasound
If a patient has a Wells score of 2 or above how should they be managed?
- Injection of LMWH until diagnosis is confirmed by doppler
- If doppler is positive, begin oral anticoagulants with vit K antagonist or novel oral anticoagulant
Name risk factors for thrombosis.
- Recent surgery
- HRT
- Combined oral contraceptive pill
- Inactivity/bedridden
Briefly outline clot formation.
Soluble fibrinogen converted to insoluble fibrin strands via a complex enzyme cascade in which zymogen precursors and activated by serine proteases.
What is Virchow’s triad?
Describes the 3 factors favoring thrombus formation.
- Stasis of blood flow: long haul flight, immobilised person
- Hypercoagulability: e.g. certain hormone therapies or pts with certain cancers
- Endothelial injury: damage to the venous system
How are patients undergoing surgery managed with regards to VTE risk
- After undergoing surgery patients are given a low dose of prophylactic anticoagulant to prevent VTE
- For patients who actually have VTE, they are given a higher dose after surgery which is a treatment dose rather than a prophylactic dose
What percentage of the general population are moderate to high risk for VTE?
2%
What percentage of DVTs are asymptomatic?
3.7-26%
What are the 2 types of heparins used in anticoagulant therapy?
- LMWHs: low molecular weight heparins
- UFHs: unfractionated heparins
When are LMWHs used?
When anticoagulant therapy is initiated.
Subcutaneous injection.
Does not require regular blood tests unlike UFHs.
Predominantly acts on factor Xa.
Also used in cancer treatment.
When are UFHs used?
For higher risk patients.
Requires IV administration and hospital admission.
APTT or KCCT blood test used.
Act on factor Xa and IIa.
What are the differences between LMWHs and UFHs?
LMWHs: average molecular weight of 4-6000 Daltons
UFHs: 15000Daltons
What agent is used to reverse the actions of UFHs?
Protamine
Protamine is not as effective in reversing actions of LMWHs.
Name a common LMWH and its side effects.
Enoxaparin
Side effects:
- Bleeding
- Heparin induced thrombocytopaenia
Name a common LMWH and its side effects.
Enoxaparin
Side effects:
- Bleeding
- Heparin induced thrombocytopaenia
What is heparin-induced thrombocytopaenia?
An immune mediated adverse reaction to heparin.
Caused by HIT antibodies of IgG class.
- Platelet factor 4 binds to heparin
- Antibody-heparin-PF4 complex leads to increased platelet activation
- Thrombosis formation in arteries and veins
- Leads to skin necrosis and injection site, acute systemic reaction, possible limb ischemia
- Discontinue heparin
Assessed using T4 score
What is the management following a suspected PE?
- Initial anticoagulation with LMWH until diagnosis is confirmed by CT pulmonary angiogram (CTPA)
- Anticoagulation with VKA (warfarin) or NOA for 6 months
Is a pulmonary embolism serious?
Yes, extremely high mortality rate (30-40,000 a year in England and Wales)
What is the most common Vit K antagonist?
Warfarin (99% of pts on VKA are on warfarin)
What are the 2 enantiomers of warfarin?
s-warfarin
r-warfarin
Describe the action of warfarin.
- Rapidly absorbed and completely bioavailable
- Has a delayed onset of action
- Long half life (36 hours)
- Typical starting dose of 2-5mg per day
