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
what is turbulent blood flow?
unpredictable and forceful
what are the causes of abnormal blood flow?
thromboembolism atheroma hyoerviscosity spasm external compression vsculitis vacsular steal
what can cause external compression of blood vessels causing abnormal flow?
a tumour pressing on the vessel
baby pressing on vessels during 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 the 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?
a thrombus forms within the vascular system during life.
A clot can occur anywhere and postmortem in the vascular system it is called a clot
give an example of a change in vessel wall that can increase the risk of thrombosis?
atheromatous plaque in artery
give an example of three typical changes which lead to thrombosis?
endothelial injury
stasis or turbulent blood flow
hypercoagulability of blood
what are line’s of Zahn?
alternating bands of red blood cells and platelets with fibrin
give a detailed description of the pathogenesis of thrombosis, starting with an atheromatous coronary artery
- atheromatous coronary artery
- turbulent flow
- loss of intimal cells from denudation of the plaque
- platelets adhere to exposed collagen
- fibrin network forms and RBCs trapped
- lines of Zahn appear
- further turbulence and platelet deposition
- leads to propagation
what can cause changes in vessel wall that leads to thrombosis?
- myocardial infaction- can lead to mural thrombosis in the heart
- turbulent flow- denuding intima
what is a mural thrombosis?
blood clot on the wall of the heart
what factors can lead to changes in blood viscosity, leading to increased risk of thrombosis?
polycythaemia, dehydrated, post-traumatic hypercoagulability
what can lead to stasis of blood flow and then thrombosis?
- long flights sitting down
- post operation (bed-bound)
what can cause turbulence of flow which can lead to thrombosis?
atheromatous plaque
aortic aneurysm
what three things do the consequences of a thrombosis depend on?
site
extent
collateral circulation
what are the favourable outcomes of thrombosis?
- resolution
- organisation and recanalisation
what are the unfavourable outcomes of thrombosis?
death
propagation leading to embolism
what is embolism?
Movement of abnormal material in the bloodstream and its impaction in a vessel, blocking its lumen
what are some of the sources of thrombi in the arterial system?
- mural thrombus
- aortic aneurysm
- atheromatous plaques
- valvular vegetations
what is a paradoxical emboli?
an embolus from a thrombus in the arterial system but has causes a pulmonary embolism (usually associated with venous thrombosis). This occurs as a result of a septal defect in the heart.
what can cause mural thrombus?
- MI
- left atrial dilatation and atrial fibrilation
what are valvular vegetations?
growths on the valves of the heart often associated with endocarditis
which sites are common for arterial emboli to get lodged in?
lower limbs
brain
other organs
the vulnerability of tissues to infarction following embolism depends on what factors?
- vulnerability of affected tissue to ischaemia
- calibre of affected vessel
- collateral circulation
where do venous thrombi embolise to?
the pulmonary circulation
what do the consequences of a pulmonary embolus depend on?
the size of the embolus. which determines the size of the artery it gets lodged in
what can occur if multiple pulmonary emboli occur over time?
pulmonary hypertension and right ventricular failure
what is a silent pulmonary embolus?
a pulmonary embolism with no clinical symptoms
what are the severe consequences of pulmonary embolism?
- pulmonary haemorrhage/ infarction
- right heart failure
- sudden death
what are the risk factors for deep venous thrombosis?
- Cardiac failure
- severe trauma/burns
- post-op/post-partum (after childbirth)
- nephrotic syndrome
- disseminated malignancy
- oral contraceptive
- increased age
- bed rest/immobilisation
- obesity
- PMH of DVT
when are patients at risk if fat embolism?
after major fractures
which parts of the body are usually affected by fat embolism?
brain, kidneys, skin
therefore it can be syndrome
when can gas embolus (of nitrogen) occur?
in decompressoin sickness (divers come up to the surface too quickley)
when can an air embolus occur?
head and neck wounds
surgey
central venous lines (catheters)
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)
when can septic material cause an embolism?
when some septic material breaks off from an infected tissue. eg. an infective endocarditis
what sort of embolism can occur in childbirth?
amniotic fluid embolism
what sort of embolism can occur as a result of fractures (and CPR)?
bone marrow embolism
when can embolisms occurefrom foreign bodies?
from medical intervention. eg. cannulae tips and sutures
what is rheumatic fever?
it is a disease of disordered immunity that occurs following the infection of a group A beta haemolytic streptococcus. It causes inflammatory changes in the heart and joints, sometimes with neurological symptoms
what are the presenting features of rheumatic fever?
flitting, painful polyarthritis of large joints
plus skin rashes and fever
recent sore through due to infectin
what inflammatory bodies form in the heart in rheumatic fever?
aschoff body
how does rheumatic fever affect the valves of the heart?
valvular stenosis
valvular regurgitation
vegetations- impair mobility
what is pacarditis and in what stage of rheumatic fever does in occur?
inflammation of the endocardium, myocardium and pericardium. it occure in the acute phase
what is rheumatic heart disease?
acute rheumatic fever can progress over time to chronic rheumatic heart disease, mainly manifesting as valvular abnormalities. and characterised principally by deforming fibrotic valvular disease
which valves are affected by rheumatic heart disease?
mitral valve- stenosis and regurgitaion
aortic-stenosis (rarely) and regurgitation
tricuspid and pulmonary valve involvement rare.
what is the most common cause of aortic stenosis?
aortic calcification valve disease
what is the most common cause of mitral regurgitation?
ischaemic heart disease
how does rheumatic heart disease affect the mitral valve?
typically leaflet thickening, commissural fusion and shortening, thickening and fusion of chordae tendineae
