Pathophysiology of thrombosis & embolism Flashcards
Normal blood flow is Laminar
What does this mean?
When a fluid flows in parallel layers, with no disruption between the layers
The central layer of fluid moves fastest, with the peripheral layer flowing slowest
With blood in larger vessels, the inner layer is where the cells mainly are, and plasma is on the outside
What determines the velocity of flow of blood?
Pressure gradient
Resistance
Viscosity
Compliance
What are the two big types of abnormal flow?
Stasis - stagnation of blood flow
Turbulence - forceful, unpredictable flow
What medical conditions/things cause abnormal flow?
Thromboembolism Atheroma Hyperviscosity Spasm External compression Vasculitis Vascular steal
What is Virchow’s triad?
3 factors that contribute to thrombosis:
- Changes in vessel walls
- Changes in blood constituents
- Changes in the pattern of blood flow
What actually is thrombosis?
Formation of a solid mass from the constituents of blood within the vascular system during life
Not a clot
Give an example of ‘changes of the vessel wall’
Atheroma
Give examples of ‘changes in the blood constituents’
Hypercholesterolaemia
Thrombophilia or post operative hypercoagulability
Hyperviscosity
Give an example of ‘changes in the blood flow’
Turbulence:
- Atheroma
- Stenosis
- Aortic aneurism
Stasis:
- Post-op
- Being stationary for ages
(overlap between vessel wall changes and blood flow changes)
How would a ruptured plaque cause thrombosis?
Ruptured plaque ∴ exposed collagen & tissue factors
Tissue factors = thrombin formation
Thrombin = fibrin formation
Fibrin meshwork created ∴ platelets adhere to fibrin and thrombus forms
A thrombus has alternating light and dark bands
What are these and what causes them to form?
Lines of Zahn
When thrombus forms:
- Platelets adhere to fibrin creating ‘platelet plaque’
- Platelet plaque traps RBC’s
- Stagnant RBC’s ∴ another plaque forms behind it
- RBC’s trapped behind second plaque
- So on & so on…
Light bands = fibrin & platelet mixture
Dark bands = RBC’s
What determines the consequences of a thrombosis?
Site
Extent
Effects on collateral circulation
What are the main clinical presentations of thrombosis?
Deep vein thrombosis - DVT
Ischaemic limb
Myocardial infarction
What is the worst thing that a thrombus can do…
Embolise
What is embolism?
Movement of abnormal material in the bloodstream and it’s impaction in a vessel, blocking it’s lumen
An embolus is a intravascular detached solid, liquid or gaseous mass
What are the types of embolus?
Systemic/arterial thromboembolus Venous thromboembolus Fat embolism Gas embolism Air embolism Tumour embolism Trophoblast embolism Septic material embolism Amniotic fluid Bone marrow Foreign bodies
What are the sources of a systemic/arterial thromboembolism?
mural thrombus (associated with MI or left atrial dilatation + AF):
- aortic aneurysms
- atheromatous plaques
- valvular vegetations
Mural = endocardial lining or lining of a large BV
What generally happens when a arterial/systemic thrombus embolises?
Travels to wide variety of sites:
Lower limbs, brain, other organs most common
Consequences depend on site & size of thrombus but usually, infarction of the tissue occurs
What is a venous thromboembolus?
Most common form of thromboembolus
Originates in deep veins of the lower limbs - DVT
Usually embolises to pulmonary circulation and may occlude pulmonary artery, the bifurcation or smaller arteries depending on size
What are the possible effects of a venous thromboembolism?
Pulmonary haemorrhage/infarction
Right heart failure
Sudden death
May be silent
Multiple PE over time:
- Pulmonary hypertension
- Right ventricular failure
What medical procedures or conditions increase risk of DVT & pulmonary thromboembolism?
Cardiac failure Severe trauma/burns Post op (+bed rest) Post partum Nephrotic syndrome Disseminated malignancy Obesity Old age
What medication increases risk of DVT & PT?
Oral contraceptives
A surgical patient is identified as high risk for DVT.
What is the next step?
Prophylaxis:
- TEDS
- s/c Heparin
What would cause a fat embolism to occur?
Major fractures
What is the effect of a fat embolism?
Syndromes affecting the brain, kidneys and/or skin
What type of embolism are divers scared of?
Decompression sickness (the bends)
This occurs when Nitrogen gas forms in the blood and lodges into capillaries
What would cause an air embolus to form?
Head and neck wounds
Surgery
CV lines (catheters)
Who is at risk of trophoblast embolisms?
Pregnant women
- embolises to lungs
Give an example of septic material embolism?
Infective endocarditis
What is the risk caused by amniotic fluid embolism?
Collapse and sometimes death in childbirth
What can cause bone marrow embolism?
Fractures:
CPR
When are you most at risk of having a foreign body embolism?
When you’re in hospital
FB embolisms are generally intravascular cannulae tips & sutures that get stuck
What is rheumatic fever?
Disease of disordered immunity caused through complications of untreated throat infection by group A strep bacteria
Characterised by inflammatory changes in the heart & joints, and sometimes neurological symptoms
Where is rheumatic fever most common?
India
Middle east
Africa
Rare in Europe and N america
How would someone with rheumatic fever typically present?
Boys > girls
5-15 years old
- Flitting (painful) polyarthritis of large joints
- Skin rashes
- Fever
Acute phase:
- Pancarditis:
- Heart murmurs
What is pancarditis?
Acute phase symptom of rheumatic fever:
Inflammation of endocardium, myocardium and pericardium
Causes heart murmurs
Can cause progression to chronic rheumatic heart disease
Patients with rheumatic fever often have had a sore throat.
Why is this?
Why does it lead to the symptoms seen with rheumatic fever?
Group A strep infection of throat
Strong antibody reaction to strep
Antibodies produced may cross react with antigens on connective tissue
Damage to the heart may be caused by antibody and T-cell mediated damage
Hence - it is autoimmune
What is a histological sign of acute rheumatic fever?
Aschoff bodies on the heart
Focus of chronic inflammatory cells, necrosis and activated macrophages (Anitschkow cells)
What three things can lead to valvular heart disease?
Valvular stenosis
Valvular incompetence
Vegetations
What is valvular stenosis?
valve thickened/calcified and obstructs normal blood flow into chamber/vessel
What is valvular incompetence?
valve loses normal function and fails to prevent reflux of blood after contraction of cardiac chamber
causes regurgitation of blood
What is vegetation?
infective or thrombotic nodules develop on valve leaflets impairing normal valve mobility; may embolise
Pancarditis in acute rheumatic fever can progress over time to ___________
Chronic rheumatic heart disease
Chronic rheumatic heart disease is mainly associated with problems of which part of the heart?
The valves
Describe how CRHD affects the valves of the heart
Inflammation of the endocardium and left sided valves results in fibrinoid necrosis of the valve cusps/chordae tendineae, over which (and along line of closure) form small vegetations
What are the overall effects of the vegetations formed chronic rheumatic heart disease?
typically leaflet thickening, commissural fusion and shortening, thickening and fusion of chordae tendineae
This causes deforming fibrotic valvular disease, particularly involving the mitral valve
Overall effect = mitral stenosis
Link CRHD with mitral stenosis
CRHD is virtually the only cause of mitral stenosis
Link CRHD with mitral regurgitation
Can sometimes cause mitral regurgitation
However, this is more commonly caused by Ischaemic heart disease
Link CRHD with aortic stenosis and regurgitation
Rarely causes aortic stenosis:
This is commonly caused by calicified aortic valve disease
Potentially still causes aortic regurgitation/incompetence
What is the involvement between CRHD and the tricuspid or pulmonary valves?
Rare involvement
