Pathophysiology of Thrombosis and Embolism Flashcards
What is a term to describe normal blood flow?
Laminar - travels smoothly and in regular paths
What are two abnormal blood flow patterns?
Turbulence
Statis
What is static blood flow?
Stagnation of blood flow - occurs due to occlusion
What is turbulent blood flow?
Forceful, unpredicatable flow
What are the causes of abnormal blood flow?
Thromboembolism
Atheroma Hyperviscosity Spasm External compression Vasculitis Vascular steal
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 are the factors of Virchow’s Triad?
Changes too blood vessel wall
Changes in the blood constituents
Changes in the pattern of blood flow
What is Virchow’s Triad?
Factors causing thrombosis
What is thrombosis?
Formation of a solid mass from the constituents of blood within the vascular system during life
Give an example of change that can occur in the vessel wall?
Atheromatous coronary artery
What are three changes that occur that lead to thrombus formation?
Endothelial injury
Stasis or turbulent blood flow
Hypercoagulability of the blood
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
Describe the stages of thrombosis
- Atheroma causes turbulent blood flow
- Loss of intimal cells from denudation of the plaque
- Platelet adhere to exposed collagen
- Forms fibrin network and trapped RBCs
- Lines of Zahn appear
- Causes further turbulence and platelet deposition
- Leads to propagation
What can cause changes to the vessel wall?
MI - can lead to mural thrombosis in the heart
Turbulent flow - denuding intima
What changes can occur to blood constituents?
Dehydration
Hyperviscosity
Post-traumatic hypercoagubility
Polycythaemia (increased Hb)
What can causes changes to blood flow (i.e. cause stasis or turbulence)?
Stasis: post-op (bed bound), long flights sitting down
Turbulence: atheromatous plaque, aortic aneurysm
What is a mural thrombosis?
Blood clot on the wall of the heart
What does the consequences of thrombosis depend on?
Site
Extent
Collateral circulation
List some clinical consequences of a thrombosis?
DVT, ischaemic limb, MI
What are favourable outcomes of thrombosis?
Resolution
Organisation and recanalisation
What are bad outcomes of thrombosis?
Death
Propagation -> embolism
What is an embolism?
Movement of abnormal material in the bloodstream and its impaction in a vessel, occluding it
What is an embolus?
Detached intravascular solid, liquid or gaseous mass
Difference between thrombosis and embolism
Thrombosis occurs when a thrombus develops in a blood vessel and reduces blood flow
Embolism occurs when a piece of thrombus, foreign object, or other bodily substance becomes stuck in a blood vessel, occluding it
What are most emboli substances?
Dislodged thrombi - thromboembolism
What are some of the sources of thrombi in the arterial system?
Mural thrombus (MI, LA dilatation and AF)
Aortic aneurysms
Atheromatous plaque
Valvular vegetations (from growth of bacteria)
What is paradoxical emboli?
An embolus which is carried from the venous side of circulation to the arterial side, or vice versa.
I.e. valvular vegetations (from vv. to aa.)
Where can systemic thromboemboli travel to in the body?
Lower limbs (common)
Brain
Other organs
What do the consequences of a systemic thromboembolism depend on?
Vulnerability of affected tissues to ischaemia
Calibre of occluded vessel
Collateral circulation but usually infarction occurs
What is the most common form of thromboembolic disease?
Venous thromboembolus - originates from deep venous thromboses (lower limb)
Where do venous thromboemboli travel to?
Pulmonary arterial circulation
Depending on size, may occlude main pul. artery, bifurcation of trunk or small arteries
What is a saddle embolus?
A large pulmonary thrombo-embolism that straddles the main pulmonary arterial trunk at its bifurcation
What are the consequences of a pulmonary thromboembolism?
Depends on size: Silent Pulmonary haemorrhage/infarction RHF Sudden death
What can multiple PEs lead to over time?
Pulmonary HPT
R ventricular failure
What are the risk factors for DVT an pulmonary thromboembolism?
Cardiac failure Severe trauma/burns Post-op/post-partum Nephrotic syndrome Disseminated malignancy Oral contraceptive Age Bed bound/immobilisation Obesity PMH of DVT
What is the management for surgical patients for prophylaxis from DVT and pul. thromboembolism?
TEDS stockings
Heparin (anticoagulant)
When are patients at risk of a fat embolism?
After major fracture
What do fat embolism affect?
Brain
Kidneys
Skin
When are patients at risk of a gas embolism?
Decompression sickness - N2 forms as bubbles which lodge in capillaries
When are patients at risk of an air embolism?
Head and neck wounds
After surgery
CV lines
List other types of embolus
Tumour Trophoblast (pregnant women - lungs) Septic material (infective endocarditis) Amniotic fluid Bone marrow (fracture i.e. CPR) Foreign bodies
What is a septic material embolism?
Embolism that is infected with bacteria, resulting in the formation of pus
What is an amniotic fluid embolism?
Amniotic fluid enters the blood stream of the mother which causes cardiorespiratory collapse and massive bleeding (coagulopathy)
What is a bone marrow embolism?
Fat tissue from the bone marrow can occlude vessels
List the type of forge in bodies which can cause an embolism
Intravascular cannulae tips
Sutures
What is rheumatic fever?
An inflammatory disease that can involve the heart, joints, skin, and brain, sometimes neurological symptoms
Where is rheumatic fever prevalent?
India
Middle East
Central Africa
and now Europe and North America
What individuals does rheumatic fever commonly affect?
5-15 yrs
Boy > girls
What does rheumatic fever present with?
‘Flitting’ (painful) polyarthritis of large joints (wrist, elbows, knees, ankles)
Skin rashes or nodules
Fever
What occurs in the acute phase of rheumatic fever?
Pancarditis (inflammation affecting endocardium, myocardium and pericardium)
Heart murmurs common
Aschoff bodies
What inflammatory bodies form in the heart in rheumatic fever?
Aschoff bodies
What are Aschoff bodies composed of?
Chronic inflammatory cells
Necrotic mycoses
Activated macrophages (anitfchkow cells)
What are three types of valvular heart disease
Stenosis
Regurgitation/incompetence
Vegetation
What is valvular stenosis?
Valve thickened/calcified and obstructs normal blood flow into chamber/vessel
What is valvular regurgitation?
Valve loses normal function and fails to prevent reflux of blood after contraction of cardiac chambers
What are valvular vegetations?
Infective or thrombotic nodules develop on valve leaflets impairing normal valve mobility and may embolise
What is pancarditis in acute rheumatic fever cause over time?
Progresses over time to chronic rheumatic heart disease, manifesting as valvular abnormalities
How does pancarditis lead to formation of small valvular vegetations?
Inflammation of endocardium and L sided valves causes fibrinoid necrosis of the valve cusps/chordae tendinae (and along line of valve closure)
What is a main feature of rheumatic heart disease?
Deforming fibrotic valvular disease (esp mitral valve)
Leaflet thickening
Commissural fusion and shortening
Thickening and fusion of chord tendinae
What is the (virtually) only cause of mitral stenosis?
Rheumatic heart disease
What valvular diseases does rheumatic heart disease cause?
Mitral stenosis Mitral regurgitation Aortic stenosis (rare) Aortic regurgitation Tricuspid valve and pulmonary valve involvement rare
