Pathophysiology of thrombosis and embolism Flashcards
What is normal blood flow described as?
laminar
What is important in blood flow?
pressure gradient, resistance, viscosity of blood, velocity, compliance
What is stasis?
STASIS: stagnation of flow
not flowing
What is turbulence?
TURBULENCE: forceful, unpredictable flow
Defects in blood flow?
Thromboembolism common
Other causes:
Atheroma
Hyperviscosity, spasm, external compression (tumour) vasculitis (inflammation of blood vessel wall), vascular steal (stolen blood)
Virchods triad?
Changes in the blood vessel wall
Changes in the blood constituents
Changes in the pattern of blood flow
What is thrombosis?
Formation of a solid mass from the constituents of blood within the vascular system during life
difference between thrombus and clot?
Pathogenesis of thrombosis?
Endothelial injury
Stasis or turbulent blood flow
Hypercoagulability of the blood
(Virchow’s triad)
Describe the stages of pathogenesis of thrombosis?
Atheromatous coronary artery
Turbulent blood flow (fibrin deposition, platelet clumping)
Loss of intimal cells, denuded plaque
Collagen exposed, platelets adhere
Fibrin meshwork, RBCs trapped
Alternating bands: lines of Zahn
thrombus causes further turbulence and platelet deposition
Propagation
Consequences
Relationship between atheroma and thrombosis?
Give examples of changes in blood flow?
Stasis: “economy class syndrome”, post-op.
Turbulence: atheromatous plaque, aortic aneurysm
Give examples of changes in blood constituents?
Examples: hyperviscosity, post-traumatic hypercoagulability
What are the common clinical scenarios of thrombosis?
DVT, ischaemic limb, MI
What are unfavourable outcomes of thrombosis?
Death
Propagation EMBOLISM-
What is embolism?
Movement of abnormal material in the bloodstream and its impaction in a vessel, blocking its lumen
What are the sources of Systemic/Arterial Thromboembolus?
Sources: mural thrombus (associated with MI or left atrial dilatation + AF); aortic aneurysms, atheromatous plaques, valvular vegetations
(Venous thrombi - paradoxical emboli)
Give characteristics of systemic thromboembolus?
Travel to wide variety of sites: lower limbs most common, brain, other organs
Consequences depend on vulnerability of affected tissues to ischaemia, calibre of occluded vessel, collateral circulation but usually infarction occurs
Describe Venous Thromboembolus?
Originate from deep venous thromboses (lower limbs)
Most common form of thromboembolic disease
Travel to the pulmonary arterial circulation
Depending on size, may occlude main pulmonary artery, bifurcation (saddle embolus), smaller arteries
Often multiple
Consequences of pulmonary thromboembolism depend on size of embolus: silent, pulmonary haemorrhage/infarction, right heart failure, sudden death
Multiple PE over time: pulmonary hypertension and right ventricular failure
Risk factors for DVT and pulmonary thromboembolism?
Cardiac failure, severe trauma/burns, post-op/post-partum, nephrotic syndrome, disseminated malignancy, oral contraceptive, increasing age, bed rest/immobilisation, obesity, PMH of DVT
Prophylaxis for surgical patients at risk: TEDS, s/c heparin
Types of emboli?
Fat
After major fractures
Syndrome of fat embolism: brain, kidneys, skin affected
Gas
Decompression Sickness
N2 forms as bubbles which lodge in capillaries
Air Embolus
Head and neck wounds, surgery, CV lines
Tumour
Spread of tumour?
Trophoblast
Pregnant women - lungs
Septic Material
For example, infective endocarditis
Amniotic Fluid
Cause of collapse (+/- death) in childbirth
Bone Marrow
Fractures; CPR
Foreign Bodies
Intravascular cannulae tips, sutures, etc
What is rheumatic disease?
Disease of disordered immunity
Inflammatory changes in the heart and joints, sometimes neurological symptoms
Commonly affects children 5-15 years, boys>girls
What are presenting features?
Presenting feature: “flitting” (painful) polyarthritis of large joints (wrists, elbows, knees, ankles) plus skin rashes and fever
Pancarditis (inflammation affecting endocardium, myocardium, pericardium) in the acute phase; heart murmurs common
Most patients have had recent sore throat, usually due to group A beta-haemolytic streptococcal infection
Strong antibody reaction to the strep: may cross-react with unknown antigens in connective tissues
Damage to heart tissue may be caused by combination of antibody-mediated and T cell-mediated reactions
What is seen in heart in acute rheumatic fever?
Focus of chronic inflammatory cells, necrosis and activated macrophages (Anitschkow cells)
What do valvular heart disease pathological problems result from?
Pathological problems result from:
Valvular stenosis: valve thickened/calcified and obstructs normal blood flow into chamber/vessel
Valvular incompetence/regurgitation/incompetency: valve loses normal function and fails to prevent reflux of blood after contraction of cardiac chamber
Vegetations: infective or thrombotic nodules develop on valve leaflets impairing normal valve mobility; may embolise
Effects of rheumatic heart disease?
Pancarditis in acute rheumatic fever can progress over time to chronic rheumatic heart disease, mainly manifesting as valvular abnormalities
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
Characterised principally by deforming fibrotic valvular disease, particularly involving the mitral valve: typically leaflet thickening, commissural fusion and shortening, thickening and fusion of chordae tendineae
What does rheumatic heart disease cause?
Virtually the only cause of mitral stenosis
Can cause mitral regurgitation but now most commonly due to ischaemic heart
disease
Now only rarely causes aortic stenosis – most due to calcific aortic valve disease
Potentially still causes aortic regurgitation/incompetence
Tricuspid valve involvement infrequent; pulmonary valve involvement rare
