W2 7 Thromboembolic Disease Flashcards
What is a thrombus?
A solid mass present within the vascular system during life formed by the constituents of blood
Differences between a thrombus and a post-mortem clot in terms of consistency, colour and adherence to vessel wall
(Useful to know if it was there before death or contributed to death)
Thrombus: firm/brittle consistency; variable colour: might be pale or red, or laminated with alternating bands of each (lines of Zahn); adherent to vessel wall
Post-mortem clot: gelatinous consistency; pale on top and dark red underneath; not adherent to vessel wall
When do pale thrombi form?
Tend to form in high flow environments (arteries/heart) due to turbulence or endothelial injury
What are pale thrombi composed of? (Image pg58)
Mainly composed of platelets
What types of pale thrombi are there?
Mural (stuck on the wall) or occlusive (depends on size of vessel)
What are the 3 causes of arterial thrombosis?
- Atherosclerosis
- Aneurysms (abnormal areas of dilatation of an artery)
- Inflammation, vasculitis
What appearances of arterial thrombosis are there?
Mural thrombosis - large vessels
Occlusive thrombosis - medium/small vessels (image pg59)
Why are Lines of Zahn formed? (Pg 60 image)
Formed due to alternating deposition of fibrin/platelets (pale) and erythrocytes (red)
Provides definitive evidence the clot formed during life
Cardiac thrombosis can form in atria, ventricle and valves. What is thrombosis in atria associated with?
Heart failure, atrial fibrillation
Cardiac thrombosis can form in atria, ventricle and valves. What is thrombosis in valves associated with?
Rheumatic fever, infective endocarditis, non-bacterial thrombotic endocarditis eg malignancy or SLE
Cardiac thrombosis can form in atria, ventricle and valves. What is thrombosis in ventricles associated with?
Myocardial infarction, cardiomyopathy
How do red thrombi form?
Usually form in veins due to stasis of blood
What makes up red thrombi?
Many enmeshed erythrocytes
What type are red thrombi?
Occlusive, propagate in direction of blood flow towards the heart
What are predisposing factors to venous thrombosis?
Immobility
Post-operative
Severe trauma
Myocardial infarction
Congestive heart failure
Pelvic mass
Thrombophlebitis (rare)
Describe the 4 stages of thrombus formation (PG63J
A. Vasoconstriction - following an injury of the endothelium
B. Primary haemostasis - primary haemostatit clot formed mainly of a platelet plug over the area of defect
C. Secondary haemostasis - involves recruitment of thrombin and fibrin to create a more mature mesh work embedded within the platelets
D. Thrombus and antithrombotic events: mature thrombus forms with associated inflammation and trapped blood cells. Lines of Zahn can accumulate with areas of platelets and fibrin followed by areas of RBC.
What is Virchow’s triad?
3 factors that promote thrombosis
What are the 3 primary factors in Virchow’s triad?
Endothelial injury (eg hypercholesterolemia, inflammation)
Hypercoagulability (inherited, acquired)
Abnormal blood flow (stasis, turbulence)
Pg64 images of thrombus development
How is a thrombus recanalised?
Over time the occlusive thrombus can be recanalised. Occurs when endothelial cells proliferate and extend within the thrombus.
What is an embolism?
A passage of insoluble mass (embolus) within the bloodstream and impaction at a site distant from its point of origin.
What is the composition of an embolism?
Thrombus (>95%)
Others (rare): fat, air/base tumour, amniotic fluid, infective/septic material
What are the sequence of events that occur in a pulmonary embolism? (Occlusion of pulmonary arteries)
- Fragmentation of venous thrombosis
- The thrombotic embolus is carries through progressively larger veins and the right side of the heart
- Lodges in the pulmonary arteries, which have a smaller diameter than the embolus
(can also arise from thrombi in RHS of the heart)
What is the sequence of events in systemic embolism?
- Fragmentation of thrombus in the left side of the heart or aorta
- The thrombotic embolus is carried through progressively smaller arteries
- Lodges in a branch of the aorta at a place where the diameter of the artery is less than that of the embolus
What is ischaemia?
Cell injury caused by the reduced blood flow to a tissue/organ or reduced venous drainage.
What are the causes of ischaemia?
Intrinsic disease of vessels
Occlusion by thrombus/embolus
External compression
What factors determine the severity of ischaemia?
Speed of onset
Extent of obstruction
Anatomy of local blood supply
Pathology of collateral circulation
General factors eg cardiac state, oxygenation of blood
Vulnerability of tissue supplied to anoxia
What is infarction?
Ischaemic necrosis caused by occlusion of either the arterial supply (common) or the venous drainage (less common) of a tissue/organ. I.e., end result of ischaemia.
Shape causing an infarction
Tend to be wedge shaped with the occluded vessel at the apex and periphery of the organ at the base
Why are white infarcts white and red infarcts red?
White colour due to lack of blood within the infarct
Red colour due to the accumulation of blood within the infarct
How does a white infarct occur?
Occurs in arterial occlusion (blockage) of solid organs with end-arterial circulation where tissue density limits the seepage of blood
Give examples of where white infarcts can occur
Heart, spleen, kidney
How does a red infarct occur?
Occurs in loose spongy tissues in venous occlusion. Dual circulation. Previous congestion, re-established blood flow at a site of previous arterial occlusion and necrosis.
Give examples of where red infarcts can occur
Lungs, small intestine, testis
