Pathophysiology of Thrombosis and Embolism Flashcards
What is normal flow of blood?
Laminar
What is meant by stasis?
Stagnation of flow
What is meant by turbulence?
Forceful unpredictable flow
What are the causes of common defects in blood flow?
Thromboembolism
Atheroma
Hyperviscosity
Spasm
External compression
Vasculitis vascular steal
What is meant by Virchow’s triad?
- Changes in the blood vessel wall
- Changes in the blood constituents
- Changes in the pattern of blood flow
What does Virchow’s triad influence?
They are the factors causing thrombosis
Give an example of a change in the vessel wall
Atheromatous coronary artery
What is the basic pathogenesis of thrombosis?
Endothelial injury
Stasis or turbulent blood flow
Hypercoagulability of the blood
What are lines of Zahn on a thrombus?
Represent bands of fibrin (lighter) with entrapped white blood cells and red blood cells (darker).
What causes the adherence of platelets?
Loss of intimal cells and the exposure of collagen
What traps red blood cells in a blood clot?
Fibrin meshwork
What is responsible for the propagation of thrombosis?
Further turbulence and platelet deposition
What is the relationship between atheroma and thrombosis?
Arterial thrombosis most commonly superimposed on atheroma; Virchow’s triad
What are the possible changes in the blood constituents (Virchow’s triad) that can result in thrombosis?
Hyperviscosity, post - operative traumatic hypercoagulability
Hypercholesterolaemia?
What are the possible alterations in blood flow (Virchow’s triad) that can result in thrombosis?
Stasis - post op “economy class syndrome”
Turbulence: atheromatous plaque, aortic aneurysm
What do the consequences of thrombosis depend on?
Site, extent and colalteral circulation
What are the resolutions of thrombosis?
Resolution
Organisation/recanalisation
Death
Propagation - embolism
What is embolism defined as?
Movement of abnormal material in the bloodstream and its impact in a vessel, blocking its lumen
What is an embolus?
Detatched intravascular solid, liquid or gaseous mass
What is a thromboembolism?
Embolus resulting from dislodged thrombus
What is a systemic/arterial thromboembolus?
Mural thrombus
Aortic aneurysms
atheromatous plaques
Valvar vegetations
Venous thrombi - paradoxical emboli
What are mural thrombi associated with?
Myocardial infarction or left atrial dilation and atrial fibrilation
Where can a systemic thrombus travel to?
Wide variety of sites: lower limbs most common, brain and other organs.
What is the usual result of a systemic thromboembolus?
Usually infarction.
Consequences depend on vulnerability of affected tissues to ischaemia, calibre of occluded vessel, collateral circulation
What is a venous thromboembolus?
Originate from deep venous thromboses (lower limbs)
Most common form of thromboembolic disease
Where do venous thromboembolus usually travel amd occlude?
Travel to the pulmonary arterial circulation, may occlude the main pulmonary artery, bifurcation or smaller arteries
What are the possible consequences of thromboembolism?
Depend on size of embolus: silent, pulmonary haemorrhage/infarction, right heart failure, sudden death
Multiple PE over time: pulmonary hypertension and right ventricular failure
What are risk factors for deep vein thrombosis and pulmonary embolism?
Cardiac failure
Severe trauma
Burns
Post op
Post partum (following childbirth)
Nephrotic syndrome
disseminated malignancy
Oral contraceptive
Increased age
Obesity
Bed rest/immobilisation
Obesity,
Past medical history of deep vein thrombosis
What is prophylaxis for deep vein thrombosis?
TEDS - long, tight fitting stockings that place mild static pressure on the legs to prevent blood from clotting
Heparin - a compound occurring in the liver and other tissues which inhibits blood coagulation.
When might you suffer from a fat embolism?
After a fracture
Syndrome of fat embolism: brain, kidneys, skin affected
What is gas embolus?
Decrompression sickness
•N2 forms as bubbles which lodge in capillaries
Apart from diving when can you get an air embolism?
Surgery - Small amounts of air often get into the blood circulation accidentally during surgery and other medical procedures (for example a bubble entering an intravenous fluid line), but most of these air emboli enter the veins and are stopped at the lungs, and thus a venous air embolism that shows any symptoms is very rare
Apart from systemic thrombus, DVT, Fat and gas what are the other types of embolus?
Tumour
Trophoblast - a layer of tissue on the outside of a mammalian blastula, supplying the embryo with nourishment and later forming the major part of the placenta.
Septic material (e.g infective endocarditis)
Amniotic fluid (cause of collapse)
Bone marrow (fractures)
Foreign bodies (Intravascular cannulae tips, sutures)
