Pathophysiology of Thrombosis and Embolism Flashcards
What defects in blood flow can result in thrombosis and embolism?
Atheroma Hyperviscosity Spasm External compression Vasculitis Vascular steal syndrome
What is normal blood flow?
Laminar - smooth and ordered
What is the vascular system affected by?
Pressure gradient
Resistance
Blood viscosity
Compliance of the vessel
What features of blood flow are abnormal?
Stasis
Turbulence
What is stasis of blood flow?
Stagnation of blood flow e.g. in cardiac failure where there is not enough force to push the blood
What is turbulence of blood flow?
Forceful, unpredictable flow e.g. due to something protruding into the lumen such as an atheromatous plaque
Noisy on auscultation
What are the components of Virchow’s triad?
Changes in blood vessel wall
Changes in blood constituents
Changes in pattern of blood flow
What is the most important risk factor for thrombus formation?
Hypercholesterolaemia
What is thrombosis?
Formation of a solid mass from the constituents of blood within the vascular system during life
What steps are involved in the pathogenesis of thrombosis?
Endothelial injury
Stasis or turbulent flow
Hypercoagulability of the blood
What effect does an atheromatous plaque have on blood flow when it starts to protrude from the lumen?
Starts to cause turbulent flow
What does turbulent blood flow cause?
Damage to the endothelial surface - loss of intimal cells and denuded plaque
What happens when the endothelial surface is lost due to turbulent flow?
Collagen in the fatty core of the plaque is exposed to the blood, platelets in the blood then stick to the collagen and form a fibrin meshwork which traps the RBCs
What do alternating bands of fibrin and RBCs form?
Lines of Zahn
What do the consequences of thrombosis depend on?
Site
Extent
Collateral circulation
What are common consequences of thrombosis?
DVT
Ischaemic limb
MI
What are possible outcomes of thrombosis?
Resolution
Organisation/recanalisation
May relieve itself but often medical intervention is needed to break down the platelets and restore blood flow
What will organisation/recanalisation cause?
Restoration of blood flow, but tissue damage may still occur as thrombus is stabilised, endothelial surface grows and fibrosis and granulation can occur along with the formation of new blood vessels
What is embolism?
Movement of abnormal material in the blood stream and its impaction in a vessel, blocking its lumen
What substances can form an embolus?
Detached intravascular solid, liquid or gaseous mass
What are most emboli formed from?
Detached thrombi
What are some causes of thromboembolism?
Systemic/arterial thromboembolism Mural thrombus Aortic aneurysm Atheromatous plaque Valvular vegetations
What are the features of a systemic thromboembolism?
Travels to a wide variety of sites - lower limbs most common but brain and other organs also affected
Usually infarction occurs
What do the consequences of a systemic thromboembolism depend on?
Vulnerability of the affected tissues to ischaemia
Calibre of occluded vessel
Collateral circulation
Where do most venous thromboembolisms originate from?
Deep venous thromboses in the lower limbs
What is the most common form of thromboembolic disease?
Venous thromboembolism
Where do venous thromboembolisms travel to? What can this cause?
Pulmonary arterial circulation
May occlude the main pulmonary artery, bifurcation or small arteries
What do the consequences of a venous thromboembolism depend on?
Size of the embolus
What are the potential consequences of venous thromboembolism?
May be silent Pulmonary haemorrhage Pulmonary infarction Right heart failure Sudden death
What do multiple pulmonary emboli cause over time?
Pulmonary hypertension and right ventricular failure
What are the possible types of embolus?
Fat Gas Air Tumour Trophoblast Septic material Amniotic fluid Bone marrow Foreign bodies
What are the risk factors for DVT and pulmonary thromboembolism?
Cardiac failure Severe trauma/burns Post-operative or post-partum state Nephrotic syndrome Disseminated malignancy OCP Increasing age Bed rest/immobilisation Obesity PMH of DVT
What does prophylaxis for surgical patients at risk of DVT and pulmonary embolism include?
TEDS and subcutaneous heparin
