Flashcards in L26. Venous Thrombosis and Pulmonary Embolism Deck (24)
What is the most commonest cause of preventible deaths in hospital environments?
What is thrombus?
A solid mass composed of blood components formed in an artery or vein during life
Is "clot" a thrombus?
Not technically. A clot is a solid mass formed post-mortem
Where do venous thrombi form?
In any vein, superficial or deep but most commonly in the deep veins of the lower limbs
What is important about the deep veins and the venous plexus surrounded by muscles?
They heavily rely on the contraction of the muscles around them (Eg. solueus muscle) to aid pushing the blood against gravity and back to the heart (against stasis)
At what location is the most common site of formation of a venous thrombus?
Around the venous valves: in a pocket just upstream or downstream of venous valves
What is the difference between venous and arterial thrombi?
Venous thrombi appear red because they form under states of stasis (high RBC content) while arterial appear pale or grey because they have high flow states (high platelet content)
What is the layering (laminated structure) of pink and red in venous thrombi?
Pink is platelets and fibrin while the red are layers of erythocytes and fibrin
Venous thrombi are usually occlusive and have the ability to propagate. What kind of thrombi are most unstable?
Recently formed venous thrombi tend to break apart from the emboli
What are the factors that predispose to venous thrombosis?
- Changes in the vessel wall
- Changes in the constituents of blood
- Changes in blood flow
What are some common primary (genetic) causes of hypercoaguability?
1. Factor V Liedin Deficiency
2. Prothrombin III deficiency
Explain Factor V Leiden Deficiency
Point mutation in Factor V prevents activated protein C, a (natural anticoagulant) from binding to a cleavage site.
What are some uncommon causes of primary (genetic) causes of hypercoaguability?
Antithrombin III deficiency
Protein C deficiency
Protein S deficiency
What are some secondary (acquired) causes of hypercoaguability?
Massive trauma and burns
Hypereostrogenic states (pregnancy and pill)
Anti-phospholipid antibody syndrome
What are the fates a venous thrombus?
1. Lysis and flow through the vessel will be restored
2. Organisation: replacement of thrombus by scar tissue (stricture/web of the vessel wall)
3. Recanalisation (most common): new blood vessels spout from the wall into the thrombus and establish new vascular channels which link up and restore blood
4. Embolise: breaks off and travels through the blood to a distant site and cause blockage of a vessel
What is an embolism?
A MOBILE mass of material within the vascular system able within a vessel, occlude its lumen and obstruct blood flow
What is a thromboembolism?
A detached piece of thrombus
What do the clinical effects of the primary thromboembolism depend on?
The size of the occluded vessel
What are the clinical presentations of small thromboemboli?
They are common and usually asymptomatic and undetected
What is a saddle embolism?
A pulmonary thromboembolus that is lodged at the bifurcation of the pulmonary artery.
What are the clinical effects of a large primary thromboembolus? How do they appear?
Sudden death or cardiac arrest with electromechanical dissociation.
- Very red with pale areas
- Coiled shape tends to reflect shape of the vein of origin
A relatively smaller pulmonary thromboembolus can lodge in either the right or left pulmonary artery (in one of them) what happens? And what clinical features?
Blood flows into one of the lungs and it is obstructed in another.
Clinical - sudden death or dyspnoea, chest pain and circulatory failure mimicking MI
What do pulmonary infarcts often look like?
Red/haemorrhage due to the dual supply to the lungs