Pathophysiology of Thrombosis and Embolism Flashcards
What effects the normal blood flow?
Pressure gradient, resistance, viscosity of blood, velocity and compliance
What is normal blood flow described as?
Laminar
What are the 2 types of abnormal blood flow?
Stasis - stagnation of flow
Turbulence - forceful and unpredictable flow
What can cause defects in blood flow?
Thromboembolism
Atheroma
Hyper-viscosity, spasm, external compression, vasculitis and vascular steal
What is Virchow’s Triad?
Changes in blood vessel wall
Changes in blood constituents
Changes in the pattern of blood flow
These are factors that cause thrombosis
What is thrombosis?
Formation of solid mass from the constituents in blood within the vascular system
Due to Virchow’s triad
What is an example of a change in vessel wall?
Atheromatous coronary artery
What is the pathogenesis of thrombosis?
Endothelial injury
Stasis or turbulent blood flow
Hypercoagulability of the blood
How does an atheroma lead to thrombosis?
Turbulent blood flow, loss of intimal cells and denuded plaque, collagen is exposed and platelets adhere, fibrin meshwork, RBCs trapped (lines of Zahn)
Further turbulence and platelet deposition - propagation
How does hypercholesterolaemia cause thrombosis?
Change in blood constituents
How does propagation of thrombus happen?
Thrombus causes more turbulent flow so causes more platelet deposition and fibrin
What is an example of a change in the vessel wall causing thrombosis?
LV wall is thin so if MI can cause dilatation of ventricle
Neural thrombosis
What are some examples in changes in the blood constituents?
Hyper-viscosity, post-traumatic hypercoagulability
Stasis - post op, economy class syndrome
Turbulence - atheromatous plaque and aortic aneurysm
What do the consequences of a thrombus depend on?
Site
Extent
Collateral circulation
What are some common clinical scenarios of thrombosis?
DVT, ischaemic limb and MI
What are the outcomes for thrombosis?
Resolution
Organisation/ recanalisation (thrombolysis)
Death
Propagation and possible embolism
Describe an embolism
Movement of abnormal material in the bloodstream and its impaction in a vessel which blocks its lumen
What is an embolus?
Detached intravascular solid, liquid or gaseous mass
What could be the sources for systemic/arterial thromboembolism?
Mural thrombus - MI, LA dilatation or atrial fibrillation
Aortic aneurysm, atheroma, valvular vegetations
What is a paradoxical emboli?
Happens due to venous thrombi
If cardiac defect
Explain systemic thromboembolism
Travel to wide variety of sites - lower limbs most common, brain..
Consequences depend on the vulnerability of tissues to ischaemia, occluded vessels and collateral circulation - usually infarction
Explain venous thromboembolism
Originated from deep venous thromboses (lower limbs)
Most common form
Travels to pulmonary arterial circulation
Often multiple
What happens if there is a big venous thromboembolism?
Can occlude main pulmonary artery and bifurcation -saddle embolus
What are some consequences of venous thromboembolism?
Silent, pulmonary haemorrhage, infarction, right heart failure and sudden death
What happens if there are multiple PE over time?
Pulmonary hypertension
Right ventricular failure
What are the risk factors for DVT and pulmonary thromboembolism?
Cardiac failure, severe burns, post-op/partum, nephrotic syndrome, disseminated malignancy, oral contraception, age, bed rest, obesity, PMH of DVT
What is given to patients who are at risk of Thromboembolism or DVT?
Prophylaxis - TEDS, heparin (anticoagulation measures)
What is a fat embolus?
Can happen after major fractures - fat breaks off
Syndrome of fat embolism - brain, kidneys and skin affected
Explain gas embolus
Decompression sickness if rise to surface too quickly
N2 forms as bubbles which lodge in capillaries
Explain air embolus
Head and neck wounds, surgery, and CV lines
Air is introduced to bloodstream
What is a tumour embolus?
Spread of tumour
Tumour can break off and go into bloodstream and possibly grow as well as occlude
When does trophoblast embolus occur?
In pregnant women - lungs
Is very rare
Describe amniotic fluid embolus?
Skin cells or keratin from baby can break off and usually go to lungs of mother
Can be very serious for mother - cause collapsing
What are some other types of embolus?
Bone marrow
Foreign bodies
Septic material
What is rheumatic fever?
Is a disease of disordered immunity
Is inflammatory changes in the heart, joints and sometimes neurological symptoms
Who does rheumatic fever usually affect?
Children between 5-15 years
Usually boys over girls
What is the presenting features of rheumatic fever?
Flitting (painful) polyarthritis of large joints (wrists, elbows, knees and ankles) plus skin rashes and fever
Pancarditis in acute phase and heart murmurs are common
What is pancarditis?
Inflammation affecting the endocardium, myocardium and pericardium
What infection are patients with rheumatic fever usually exposed to?
Group A beta-haemolytic streptococci infection
How does strep. infection lead to rheumatic fever?
Strong antibody reaction to strep. - may cross react with unknown antigens in connective tissue
Damage to heart tissue may be caused by combination of antibody-mediated and T-cell mediated reactions
Explain an Aschoff Body
Seen in heart of acute rheumatic fever
Focus of chronic inflammatory cells, necrosis and activated macrophages (antischkow cells)
What are some causes of valvular heart disease?
Valvular stenosis
Valvular incompetence/regurgitation
Vegetations
What is valvular stenosis?
Valve thickened/calcified and obstructs normal blood flow into chamber/ vessel
What is valvular incompetence or regurgatation?
Valve loses normal function and fails to prevent reflux of blood after contraction of cardiac chamber
What is vegetations?
Infective or thrombotic nodules develop on valve leaflets impairing normal valve mobility - may embolise
What does chronic rheumatic heart disease usually manifest as?
Valvular abnormalities
What does inflammation of endocardium and left sided valves result in?
Fibrinoid necrosis of valve or cusps/ chordae tendinea, over which form small vegetations
Explain rheumatic heart disease?
Characterised by deforming fibrotic valvular disease - involving the mitral valve
Typically leaflet thickening, commissural fusion and shortening, thickening and fusion of chordae tendineae
What does rheumatic heart disease cause?
Mitral stenosis
Mitral regurgitation is rare
Aortic stenosis and regurgitation is rare
Pulmonary valve and tricuspid is rare
What is the appearance of mitral valve in rheumatic heart disease?
Fish mouth appearance
Very thin and stenosed
