Thrombosis And Embolism Flashcards
What is thrombosis
Process leading to formation of thrombus
What is a thrombus
Blood clot
Solid mass made of blood constituents which have aggregated together in flowing blood of the lumen of a blood vessel
What are the main constituents of a thrombus
Platelets and fibrin
What types of thrombosis are there?
Physiological and pathological
When is thrombosis a normal mechanism?
Preventing bleeding when a vessel wall is breached
When does thrombosis become pathological
When it is not controlled by fibrinolysis
Describe normal thrombosis
Vessel wall breached
Circulating platelets aggregate to plug gap
Platelets release factors which trigger cascade
Cascade converts fibrinogen to fibrin
Fibrin bind together platelets and entrap WBCs and RBCs
What is fibrinolysis
Breaking down of fibrin so the thrombus dissolves
Plasmin is the enzyme
Broken down products are the fibrin degradation products
What occurs to control the side of the thrombus
Plasminogen converted to plasmin by plasminogen activator (tissue plasminogen activator)
Plasminogen and t-PA bund to fibrin
t-PA converts nearby plasminogen to plasmin which begins to degrade the fibrin
Describe pathological thrombosis
Occurs when thrombus enlarges beyond vessel healing requirements and continues to grow
Beyond certain thrombus size and rate of development, intrinsic fibrinolytic system is incapable of controlling size of thrombus
How does the thrombus grow in pathological thrombus?
Accretion of layer upon layer
If it continues unrestrained, reddish-brown mass is produced in vessel
What are D-dimers?
Breakdown product of a fibrin mesh, stabilised by factor XIII
What factors predispose thrombus formation?
- Damage to vessel wall (endothelium)
- Stasis (slow or turbulent)
- Change in character of blood (increased platelets, RBCs)
Where does pathological thrombosis occur?
Arteries
Veins
Heart
Most prominent predisposition factor of arteries?
Vessel wall damage
Most prominent predisposition factor of veins?
Stasis
Most prominent predisposition factor of the heart?
Ventricles - chamber wall damage
Atrium - stasis
Heart valves - valve surface damage
What effect will a thrombus forming an atheroma in a coronary artery?
Tissue will become ischaemic
Tissue death due to reduced blood flow - infarction
What effect will a thrombus formed in a vein in a leg cause?
Stays there - swollen leg
Moves - pulmonary embolism
What effect will a thrombus formed in a heart chamber cause?
Inflammation, sticky, thrombus forms
Stroke (left ventricle)
What woukd white markings be in a heart?
Scarring from MI
What effect would a thrombus on mitral valve cause?
Same as having thrombus in left ventricle
What happens to thrombus?
Lysed by intrinsic fibrinolysis - rare Completely block lumen - occlusion Undergo organisation and recanalisation Extend locally - propagation Fragment or detach and travel elsewhere- thromboembolism
What happens when a thrombus occludes a vessel?
Artery - stops flow of blood, cuts off oxygen to issue - infarction
Vein - prevents venous drainage of tissues, blood pools - congestion and infarction (often haemorrhagic)
What occurs if the thrombus organises and recanalises?
New vessels grow into thrombus
Vascular granulation tissue develops
Fibroblasts invade and deposit collagen
Fibrovascular granulation tissue develops
Embolism
Transference is abnormal material by blood stream with eventual impact action of the material in a vessel distal to origin
Most important materials to embolise
Thrombus
Cancer cells
Where does a thrombus in an artery or left side of the heart embolise to?
Systemic arterial system
What will a blockage of brain arteries cause?
Stroke
What will blockage of lower limb arteries cause?
Gangrene of legs
What will blockage of mesenterric arteries cause?
Bowel necrosis
What will blockage of renal arteries cause
Kidney infarct
What will blockage of splenic artery cause
Splenic infarct
Where will a thrombus in a systemic vein embolise to?
Pulmonary artery branch - pulmonary embolus
Impact of pulmonary embolus on patient
Small - small peripheral lung infarct
Large - sudden death
Examples of systemic emboli
Thrombus in mitral valve - tissue necrosis in kidney
Left ventricular wall - brain, secondary haemorrhage
Calf - pulmonary embolism
What is a VTE risk assessment ?
Risk assessment for venous thromboembolism
How does VTE RA work?
Active cancer treatment/cancer Age >60 Dehydration Known Obesity One or more significant medical Personal or first degree relative Hormone replacement therapy Oestrogen containing contraceptive Varicose veins with phlebitis Pregnancy
Other materials that are embolised
Fat and marrow
Air
Nitrogen
Amniotic fluid
D-dimer test
Diagnose thrombus presence
If negative for D-dimer, unlikely to have serious venous blood clot
What is infarction
Special kind of necrosis due to reduced blood flow
