22. Pathophysiology of Thrombosis and Embolism Flashcards
How is normal blood flow described as?
Laminar; when blood flows in parallel layers with no disruptions between layers
What properties make blood flow laminar in normal conditions? (5)
- pressure gradient
- resistance (due to diameter)
- viscosity of blood
- velocity of blood
- compliance (muscular arteries less compliant than elastic)
What is the term that describes stagnant blood flow?
Stasis
What is the term that describes forceful and unpredictable flow?
Turbulence (blood swirling around, not smooth, rhythmic or laminar)
What is the most common defect in blood flow?
Thromboembolism
What are other causes for defects in blood flow?
- atheroma
- hyperviscosity
- spasm
- external compression (e.g. tumour)
- vasculitis (inflammation of vessel wall)
- vascular steal
What is the name of the group of factors that cause thrombosis?
Virchow’s Triad
What 3 factors make up the Virchow’s Triad which cause thrombosis?
- changes in blood vessel wall (endothelial injury/ dysfunction)
- changes in blood constituents (hypercoagulability; increase in clots)
- changes in pattern of blood flow (haemodynamic changes e.g. stasis or turbulence)
What is the difference between clot and thrombus?
Thrombus: formation of a solid mass from the constituents of blooth within the vascular system during life; i.e. when it’s dangerous in a healthy blood vessel
Clot: outwith vascular system or formed in a health vessel as a response to damage to a vascular tissue
What 2 constituents make up an atheroma?
- fibrous cap
2. lipid core
What is the main pathogenesis of changes to blood vessel wall causing a thrombus?
endotherlial injury/dysfunction
What is the main pathogenesis to blood flow causing a thrombus?
stasis or turbulent blood flow (abnormal blood flow)
What is the main pathogenesis to changes in blood constituents which causes a thrombus?
Hypercoagulability of the blood (increase in coagulation which causes a thrombus)
What occurs on the endothelial lining in the blood vessel when a thrombus is formed?
endothelial surface is lost which causes RBCs and platelets to be deposited on plaque forming the thrombus
Describe the steps which occur when thrombosis occurs. (8)
- atheromatous coronary artery exists
- turbulent/rapid blood flow occurs leading to fibrin deposition and platelet clumping
- loss of intimal cells and denuded/stripped plaque
- collagen is exposed and platelets adhere/ stick to it
- fibrin meshwork forms and RBCs are trapped
- alternating bands; lines of Zahn (layers of platelets mixed with fibrin and dark RBCs characteristic of thrombus)
- leads to further turbulence and platelet deposition
- propagation/spreading and consequences
What is the biggest risk factor for atheromas and thrombosis which are caused by Virchow’s triad?
Hypercholesterolaemia
What is arterial thrombosis most commonly formed/ imposed on?
most commonly formed on atheroma (atheromatous plaque) which indicates relationship between atheroma and thrombosis
What are lines of Zhan?
- characteristic of a thrombi
- visible layers (laminations) of platelets, fibrin meshwork and RBCs
- its presence indicates thrombosis due to turbulent blood flow
Where is the turbulent flow greatest?
At the end of a thrombus
What is meant by turbulent flow?
- fluid undergoes irregular fluctuations and mixing (in contrast to laminar flow where fluid moves in smooth and parallel layers)
- speed of fluid is continuously undergoing changes in both magnitude and direction
Define thrombosis.
- LOCAL coagulation or clotting of blood in a blood vessel (not travelling but localised blood clot).
- Thrombus formed due to changes in blood vessel wall
Give an example of when blood constituents often change which leads to thrombosis.
When blood undergoes hyperviscosity and post-traumatic hypercoagulaility after a trauma/injury or post surgery as an automatic mechanism
When is stasis blood flow most common?
- “economy class syndrome”
- common in post- op as blood travels more slowly
When is turbulent blood flow most common?
- when there is an atheromatous plaque
- when possibility of aortic aneurysm (excessive localised swelling of the artery wall causing vessel dilatation)
What do thrombosis consequences depend on?
- site of thrombus
- extent of thrombus
- collateral circulation
What are common clinical scenarios for thrombosis patients? (3)
- DVT (deep vein thrombosis)
- ischaemic limb
- myocardial infarction
What are possible outcomes for thrombosis?
- Resolution (resolves) where thrombus goes away all together through fibrinolysis and fibrin meshwork breaks down as thrombolytic agents restore blood flow
- organisation/ recanalisation with the help of therapeutic agents
- propagation (travelling of thromobus) leading to an embolism (travelled and caused blockage at a distant site to the origin)
- death; if oxygen supply cut off
Define embolism.
- MOVEMENT of abnormal material in the bloodstream and its impaction in a vessel, blocking/obstructing its lumen
Define embolus.
- detached intravascular solid, liquid or gaseous mass that travels
Does embolism HAVE to be a thrombus?
- It doesn’t have to be only thrombus but most are (can also be other things)
- Most emboli are dislodged thrombi (thromboembolism)
What do factors causing embolism depend on?
type of embolus which causes the obstruction
What are the main sources of a systemic/ arterial thromboembolus? (4)
- mural thrombus; in contact with endocardial lining of cardiac chamber or with a wall of a large vessel if not blocking (associated with MI or left atrial dilatation + atrial fibrillation
- aortic aneurysm
- atheromatous plaques
- valvular vegetations
What is a paradoxical emboli?
- venous thrombi
- embolism which travels to the arterial side through a lateral opening in the heart such as patent forament ovale or arteriovenous shunts in the lungs
What are the most common sites for a systemic thromboembolus? (3)
- lower limbs (most common)
- brain (cerebral arteries)
- other organs
What do consequences of a systemic thromboembolus depend on?
- vulnerability of affected tissues to ischaemia
- calibre (diameter) of occluded vessels
- collateral circulation
What is the most likely consequence of a systemic thromboembolus?
Infarction (obstruction of blood supply to tissues causing local tissue death)
What is the most common form of thromboembolic disease? Where does it originate from?
venous thromboembolus; originates from deepvenous thromboses (lower limbs)
Where does venous thromboembolus travel to and occlude?
- pulmonary arterial circulation
- can occlude pulmonary artery, smaller arteries or bifurcation
What is the name for venous thromboembolus which occludes at the bifurcation?
saddle embolus
What does location of venous thromboembolus obstruction depend on?
depends on the size of the venous thromboembolus
What are possible consequences of a venous thromboembolus? (5)
- silent (no symptoms at first)
- pulmonary haemorrhage/ infarction
- right heart failure
- sudden death
- multiple pulmonary emboli over time, with pulmonary hypertension and right ventricular failure
What are the risk factors for DVT and pulmonary thromboembolism? (10)
- cardiac failure
- severe trauma/burs
- post-op/post-partum
- nephrotic syndrome
- disseminated malignancy
- oral contraceptive
- increase age
- bed rest/immobilisation
- obesity
- past medical history of DVT
Why does DVT (deep vein thrombosis) often occur and originate from the lower limbs?
- Immobility causes blood in veins to be slow
- Slow moving blood is more likely to clot than normal- flowing blood
In what circumstances is there lack of mobility which can increase risk of DVT and therefore pulmonary thromboembolism? (3)
- After surgical operation; under anaesthetic, patient asleep for hours since muscle temporarily paralysed, especially in leg or pelvis operations
- Any leg or injury that causes immobility; e.g. plaster cast or anaesthetic
- Long journeys by plane, train or coach/car; due to not moving legs a lot and sitting in same position for long periods
What is used as prophylaxis measure (preventive) for DVT and pulmonary thromboembolism? (2)
- TEDS; thromboembolic disease support
2. heparin (blood thinner)
What are different types of possible embolus? (12)
- fat
- gas
- air embolus
- tumour
- thophoblast
- septic material
- amniotic fluid
- bone marrow
- foreign bodies
- thromboembolism
- tissue embolism
- cholesterol embolism
What is a fat embolus?
- embolism of fat droplets or bone fracture
- most common after major fractures
- syndrome of fat embolism; brain, kidneys and skin affected
What is a gas embolus?
- decompression sickness
- N2 forms as bubbles which lodge in capillaries
What is air embolus?
- embolism of air bubbles
- head and neck wounds, surgery and CV lines often cause it
What is tumour embolus?
spread of tumour/ tumour fragments
What is throphoblast embolus?
- pregnant women have it; in the lungs
- material from the placenta detaches and gets into mother’s circulation (rare)
What is septic material embolus?
- embolism of bacteria-contaning pus
- for example, infective endocarditis
What is amniotic fluid embolus?
- cause of collapse in childbirth
- embolism of amniotic fluid, foetal cells, hair, or other debris that enters the mother’s bloodstream via the placental bed of the uterus
- triggers an allergic reaction.
What is bone marrow embolus?
- due to fractures or CPR (bits break off and travel)
What is foreign bodies embolus?
- intravascular cannular tips, talc sutures etc and other small objects
What is thromboembolism?
thrombus (blood clot) is is partially or completely detached from a site of thrombosis (clot) in a blood vessel and bloodstream then carries embolus where it can block vessel cavity
What is tissue embolus?
embolism of small fragments of tissue which travel to different sites through bloodstream
What is cholesterol embolus?
- embolism of cholesterol often from atheromatous plaque inside a vessel
