Pathophysiology of Thrombosis and Embolism Flashcards
What are the two types of abnormal blood flow?
stasis
turbulent
What is static blood flow?
stagnation of flow e.g. haemostasis
How would you describe turbulent blood flow?
2
unpredictable and forceful
What are causes of abnormal blood flow?
7
thromboembolism atheroma hyperviscosity spasm external compression vasculitis vacsular steal
What can cause external compression of blood vessels causing abnormal flow?
(2)
- tumour
- pregnancy
What is vascular steal?
Dilation of one vascular network (e.g., during exercise or vasodilator therapy) “steals” blood flow from another region within the organ that is already maximally dilated because of the presence of proximal lesions.
What is Virchow’s triad of factors causing thrombosis?
- changes in the blood vessel wall
- changes in the blood constituents
- changes in the pattern of blood flow
What is the difference between a thrombus and a clot?
Clot forms in stagnated blood (RBC + fibrin)
Thrombus forms within blood vessels during life (when blood is moving).
Give an example of a change in vessel wall that can increase the risk of thrombosis?
atheromatous coronary artery
Give an example of three typical changes which lead to thrombosis?
- endothelial injury (clotting cascade = fibrin)
- stasis or turbulent blood flow (atheroma)
- hypercoagulability of blood (increased viscosity in smokers)
Outline the pathogenesis of thrombosis.
6
- atheromatous plaque
- turbulent blood flow
- loss of intimal cells, collagen exposed
- fibrin meshwork and RBC stagnate, platelet aggregation
- Lines of Zahn
- propagation
What are line’s of Zahn?
Alternating bands of fibrin and platelet thrombi and RBC clots.
They appear in bands of cream and dark red.
Arterial thrombosis is most commonly superposed on what?
What increases the likelihood of this?
atheroma
hypercholesterolaemia
What can cause changes in vessel wall that leads to thrombosis?
(5)
- MI - can lead to mural thrombosis in the heart.
- trauma
- smoking
- hypertension
- atheroma
What is a mural thrombosis?
Mural thrombi are thrombi that adhere to the wall of a blood vessel. They occur in large vessels such as the heart and aorta.
What factors can lead to changes in blood constituents, leading to increased risk of thrombosis?
(3)
- polycythaemia
- hyperviscosity (e.g. smoking)
- post-traumatic hypercoagubility
What is meant by changes to blood flow which can lead to thrombosis?
(2)
- stasis
- turbulence
What can lead to stasis of blood flow and then thrombosis?
2
- long flights sitting down (“economy class syndrome”, DVT)
- post operation (bed-bound)
What can cause turbulence of flow which can lead to thrombosis?
(2)
atheromatous plaque
aortic aneurysm
What three things do the consequences of a thrombosis depend on?
- site
- extent
- collateral circulation
What are the common consequences/outcomes of thrombosis?
- myocardial infarction
- DVT (PE)
- critical limb ischaemia
What are the hopeful outcomes from thrombosis?
2
- resolution
- organisation/recanalisation
What does propagation of thrombosis lead to?
embolism (thromboembolism)
What is an embolism?
Give examples.
Movement of abnormal material in the bloodstream and its impaction in a vessel, blocking its lumen.
It could be anything: blood, brick dust, air.
What are most emboli?
Dislodged thrombi i.e. thromboembolism
What are some of the sources of thrombi in the systemic/arterial system?
(4)
- mural thrombus
- aortic aneurysm
- atheromatous plaques
- valvular vegetations
What is a paradoxical emboli?
A paradoxical embolism refers to an embolus which is carried from the venous side of circulation to the arterial side, or vice versa.
What is the most common site where thromboembolisms travel to?
lower limbs
What do the consequences of a thromboembolism depend on? (3)
What do they usually end up in?
- vulnerability of affected tissues to ischaemia
- calibre of occluded vessel
- collateral circulation
Infarction
Where do venous thrombi embolise to?
What is the name of the clinical emergency associated with severe cases of this?
pulmonary circulation
pulmonary embolism
What do the consequences of a pulmonary embolus depend on?
2
- the size of the embolus.
- this determines the size of the artery it gets lodged in.
What are the consequences of severe pulmonary thromboembolism?
(4)
- pulmonary haemorrhage
- infarction
- right heart failure
- sudden death
What can multiple pulmonary emboli over time lead to?
- pulmonary hypertension
- right ventricular failure
What is a silent pulmonary embolus?
a pulmonary embolism with no clinical symptoms
What are the risk factors for deep venous thrombosis?
10
- cardiac failure
- severe trauma/burns
- post-op/post-partum
- nephrotic syndrome
- disseminated malignancy
- oral contraceptive
- increased age
- bed rest/immobilisation
- obesity
- PMH of DVT
What prophylaxis measures are taken for surgical patients at risk of thrombosis/thromboembolism?
- s/c heparin
- TEDs
What is heparin?
anticoagulant
When are patients at risk if fat embolism?
after major fractures
Which parts of the body are usually affected by fat embolism?
(3)
brain, kidneys, skin
affected
When can gas embolus (of nitrogen) occur?
Give an example.
in decompressoin sickness (divers come up to the surface too quickley)
When can an air embolus occur?
3
- head and neck wounds
- surgery
- CV lines
What is a trophoblast embolism?
material from the placenta dislodges and enters the maternal blood stream
When can a tumour cause an embolism?
part of the tumour detaches and spreads to another part of the body (metastasises)
Give an example of when septic material can cause an embolism?
Infective endocarditis
What sort of embolism can occur in childbirth?
What can this cause?
amniotic fluid embolism
collapse +/- death
What sort of embolism can occur as a result of fractures (and CPR)?
bone marrow
When can embolisms occur from foreign bodies?
from medical intervention. eg. cannulae tips and sutures
What is rheumatic fever?
a disease of disordered immunity
When might rheumatic fever develop?
following the infection of a group A beta haemolytic streptococcus e.g. throat infection.
How does rheumatic fever present?
4
- “flitting” (painful) polyarthritis of large joints (wrists, elbows, knees, ankles)
- skin rashes
- fever
- recent throat infection
How does rheumatic fever affect the heart?
How?
- pancarditis
- heart murmurs common
Damage to heart tissue may be caused by combination of antibody-mediated and T cell-mediated reactions.
What inflammatory bodies form in the heart in rheumatic fever?
aschoff body
How does rheumatic fever affect the valves of the heart?
3
- valvular stenosis
- valvular regurgitation
- vegetations- impair mobility, may embolise
When does pancarditis present in rheumatic fever?
What can it progress to?
acute phase
progresses to chronic, manifesting as valvular abnormalities.
Which valves are affected by rheumatic heart disease?
L side
mitral mainly
What is the pathogenesis of fibrotic valvular disease?
3
- leaflet thickening
- commissural fusion
- shortening/thickening and fusion of chordae tendineae
What is the most common cause of aortic stenosis?
calcific aortic valve disease
What is the most common cause mitral regurgitation?
ischaemic heart disease
What is virtually the only cause of mitral stenosis?
rheumatic heart disease
