Wk 6 Anticoagulants & Atrial Fibrillation

Question 1

Describe the three stages of haemostasis

Answer 1

Vascular spasm - vasoconstriction

Platelet aggregation - plug formation

Coagulation - clot formation

Anticoagulant targets:

i. Deep venous thrombosis (DVT)
ii. Prophylaxis for venous thromboembolism
iii. Pulmonary embolism (PE)
iv. Atrial fibrillation (AF)

1. Thrombus：宅着附着血管壁
2. Embolus：旅行
3. Thromboxane：缩血管《。》
4. Prostacyclin：开血管《O》

Question 2

Explain how low dose aspirin exerts its antiplatelet effect

Answer 2

MOA: inhibits platelet coagulation by ↓ the production of thromboxane A2 (COX1 → TXA2)

Question 3

Understand the difference between a thrombus and an embolus

Answer 3

o Thrombus — a clot that forms in a vessel and remains there
o Embolus — a clot that forms in one location and travels to another

Question 4

Discuss the mechanism of action of Heparin

Answer 4

MOA: combined with antithrombin III to promote its effect of inhibiting thrombus formation

NP: prophylaxis of VTE for surgical PT, treatment for MI

CON: platelet depletion, hepatorenal impairment

AEs: bleeding/bruising, hyperkalemia (heparin inhibits aldosterone), platelet depletion

Question 5

Discuss the mechanism of action of Warfarin

Answer 5

Drug class: anticoagulants
MOA: inhibits the synthesis of Vit K and Vit K dependent clotting factors

NP:

• monitor INR (international normalised ratio) to be within 2~3
• keep a normal diet and steady intake of Vit K

CON: alcoholism (affect warfarin effects), platelet depletion, surgery/pregancy

AEs: bleeding

Question 6

Discuss the mechanism of action of DOACs

Answer 6

DOACs - direct oral anticoagulants
Benefits: fast onset (30 mins), convenient with no ongoing monitoring
Dabigatran
MOA: inhibits the action of thrombin in converting the fibrinogen to fibrin, and thus ↓ clot formation
CON:
- risk of bleeding, ie haemorrhagic stroke
- hepatorenal impairment
- AF/heart valve disease
AEs: gastritis, dyspepsia, GI bleeding

Factor Xa Inhibitor
MOA: selectively inhibit factor Xa, and inhibit conversion of fibrinogen to fibrin → ↓thrombus development.
Apixaban
CON: 
- risk of bleeding, ie haemorrhagic stroke
- hepatorenal impairment
- AF/heart valve disease
AEs: nausea, platelet depletion

Rivaroxaban
CON:
- risk of bleeding, ie haemorrhagic stroke
- hepatorenal impairment
- AF/heart valve disease
AEs: nausea, platelet depletion

Question 7

Discuss the monitoring required with anticoagulant therapy

Answer 7

• watch for the warning signs of bleeding, ie bruising, dark urine
• monitor INR, target 2~3

Question 8

Be aware of the major drug interactions which may occur with anticoagulant therapy

Answer 8

Warfarin drug interaction:

• NSAIDs, ie aspirin, ibuprofen
• SSRIs
• paracetamol
• statins
• St John’s wort
• garlic/cranberries/alcohol

Avoid a low vitamin K diet – eat a normal, balanced diet
Dabigatran, Rivaroxaban, Apixaban: less drug interactions than warfarin

Question 9

Describe atrial fibrillation, discuss its treatment options and explain why it may lead to ischaemic stroke

Answer 9

Def.: a heart dysrhythmia in which the heart beats irregularly (atrium quivers)

Treatment:
- Rhythm control: use ‘Atrial Fibrillation Ablation’ method to reverse AF to sinus rhythm
- Rate control: using drugs to slow the conduction rate of AV node
> BB: atenolol, AE hypotension
> CCB: verapamil, AE bradycardia, hypotension
> Digoxin: impede Na+/Ca++ pump, cause Ca++retention, AE bradycardia

Risk of IS:

• clots/thrombus formed in the atrium (always left-sided atrium)
• every person with rate control AF must be on an anticoagulant e.g. warfarin or a DOAC to stop the clotting that happens in AF

Question 10

What is the stroke risk assessment in people with non-valvular AF?

Answer 10

CHA2DS2-VASc score:
1 - congestive HF/or history
1 - HTN
1 - > 75 y/o
1 - DM
2 - stroke or transient IS history

0 means “low risk”, 1 means “moderate risk”, >1 means “high risk”