Haemostasis 5 Flashcards
What is a thrombus?
A solid mass in a blood vessel or heart
Process is called thrombosis
What makes up a thrombus?
Variable amounts of platelets, fibrin, trapped red cells
What is Virchow’s Triad and how does it relate to thrombosis?
Abnormal blood flow
Endothelial damage
Hypercoagubility
- varying combinations of these 3 factors cause thrombosis
How does endothelial injury contribute to thrombosis?
Exposes vWF, collagen, tissue factor
Permits platelet adhesion
How does altered blood flow contribute to thrombosis?
Veins: stasis - accumulation of activated coagulation factors and activated platelets
Arteries: activation of platelets and vWF = activated by turbulent flow/high shearing stress
How does Hypercoagubility contribute to thrombosis?
Veins - increased concentration of coagulation factors or reduced functional levels of coagulation inhibitors
Arteries - some autoantibodies may trigger thrombosis
What are common causes for endothelial injury?
Endocardial injury - following MI, heart valve disease
Arterial injury - ulcerated/ruptured atherosclerotic plaque, agents toxic to endothelium, haemodynamic stress
Inflammation affecting blood vessels - vasculitis, trauma
When does a mural thrombus often form and why?
Mural thrombus on the endocardium after an MI.
- Endothelium survives, but is injured by products from ischaemic and necrotic underlying muscle.
- Stasis occurs between inactive trabeculae
- Patients with MI have risk factors for increased coagulability
Describe how loss of laminar flow in arteries contributes to thrombosis.
High flow rates result in turbulence.
Causes endothelial injury through shearing stresses and activation of adhesion receptors.
Platelet activation
Activated platelet impact on and adhesion to endothelium.
Which arteries are sites of turbulence and are at risk of atherosclerosis and mural thrombosis?
Aorta and branches
When does stasis in veins occur?
During surgery and in patients lying still
Pressure on calf muscles, lack of movement
What issues surround stasis in veins?
Low flow or intermittent flow or no flow
Endothelial cell activation is promoted - platelets adhere
More platelets contact the vessel wall if blood is not flowing
How does surgery and trauma relate to stasis of the veins in the LL?
Activated coagulation factors and platelets in circulation
- Not washed away and dilluted by blood flow
-Not inactivated if concentration increases too rapidly
Small thromboses form
- may propagate (extend/grow)
- may undergo fibrinolysis
Describe how the development of a venous thrombus occurs.
Dynamic process over time.
- Blood must flow past developing thrombus for platelets and fibrin activation to propagate (extend) the thrombus
- Does not adhere well to wall
- Fragments may break off and form a thrombotic embolus
Thrombus attached firmly at injury site
What is hypercoaguability?
Any alteration of coagulation pathways increases the risk for thrombosis
Often multifactorial
- genetic or acquired
- increased concentration of coagulation proteins
- decreased concentration of coagulation inhibitors
- most common factor: inflammation
Name the consequences of thrombosis.
Arterial thrombosis - ischaemia and infarction
Describe how thrombosis in a diseased artery occurs.
Usual predisposing factor is rupture of an atherosclerotic plaque. This triggers platelet aggregation, fibrin formation and extension of thrombus to occlude vessel.
What is the consequence of venous thrombosis?
Pulmonary embolus - thrombotic embolus lodged in pulmonary artery
What are acute consequences of venous thrombosis?
Local pain and oedema (swelling)
Valves often lost from veins
Pulmonary embolism
What are chronic consequences of venous thrombosis?
Raised pressure in veins Varicose veins Chronic ulcers at ankle after minimal trauma Chronic pain in leg Swelling
What happens in varicose veins?
Vein diameter increases and vein elongates under sustained pressure due to incompetent valves
What are further consequences of venous thrombosis?
Recurrent thrombosis
Recurrent pulmonary embolism
What is thrombophilia?
Increased risk for thrombosis
- acquired or genetic
- arterial or venous
- may be multifactorial
What are common risk factors for arterial thrombosis?
Hyperlipidaemia HTN Diabetes Cigarette smoking Male Family Hx Polycythaemia Elevated fibrinogen Homocysteine
