Pathophysiology of Atheroma Flashcards
What is the definition of atheroma/atherosclerosis?
•Formation of focal elevated lesions (plaques) in intima of large and medium-sized arteries
What are potential outcomes of atheroma?
Ischaemia in coronary arteries - atheromatous plaques narrowing lumen
Angina due to myocardial ischaemia
Complicated thromboembolism
What is arteriosclerosis?
Stiffening or hardening or the arterial walls which features smooth muscle hypertrophy, apparent reduplication of internal elastic laminae and intimal fibrosis leading to a decrease in vessel diameter.
When is the difference between arteriosclerosis and atherosclerosis?
Atherosclerosis is a type of arteriosclerosis
When are the effects of arteriosclerosis most apparent?
When the CVS is further stressed by haemorrhage, major surgery , infection or shock
Who commonly suffers from arteriosclerosis?
Elderly
What is the earliest significant lesion of atheroma?
Fatty streak
What makes up the yellow linear elevation of intimal lining?
Comprises masses of lipid - laden macrophages
Who often gets early atheromatous plaques?
Young adults onwards - fatty streaks are present in children although they may disappear
What does early atheromatous plaque progress to?
Established plaques
What are the structural features of a fully developed atheromatous plaque?
Central lipid core with fibrous tissue cap - covered by arterial endothelium
What is responsible for the collagen production in the cap?
Smooth muscle cells
What is the function of the fibrous cap that sits on the central lipid core?
Provides structural strength
What resides in the fibrous cap?
Inflammatory cells - macrophages, T lymphocytes and mast cells - recruited from the arterial endothelium
What is contained within the central lipid core?
Cellular lipids/debris derived from macrophageswhich have died in the plaque
Often a rim of foamy thrombogenic macrophages
Why are some macrophages described as foamy?
Due to the uptake of oxidised lipoproteins via specialised membrane bound scavenger receptor
What marker in angiograms forms in late plaque development?
Dystrophic calcification
What is dystrophic calcification?
Dystrophic calcification (DC) is the calcification occurring in degenerated or necrotic tissue
Where does atheroma normally occur?
•Form at arterial branching points/bifurcations (turbulent flow)
What is meant by a complicated atheroma?
Haemorrage into plaque causing plague rupture and potential thrombosis
Define haemorrhage
an escape of blood from a ruptured blood vessel.
What is the most important risk factor for atheroma?
Hypercholesterolaemia
How may increased LDL cholesterol levels arise?
•lack of cell membrane receptors for LDL
What are signs of major lipidaemia?
Familial
Biochemical evidence (LDL, HDL, total cholesterol, triglycerides)
- Corneal arcus (premature)
- Tendon xanthomata (knuckles, Achilles)
- Xanthelasmata – fatty lumps on the eyelid
What are the risk factors for atheroma?
- Smoking
- Hypertension
- Diabetes mellitus
- Male
- Elderly
- Accelerate process of plaque formation driven by lipids
What are the less strong risk factors?
- Obesity
- Sedentary lifestyle
- Low socio-economic status
- Low birthweight
- role of micro-organisms
What is the two step development process of athermoatous plaques?
- injury to endothelial lining of artery
- chronic inflammatory and healing response of vascular wall to agent causing injury
•Chronic/episodic exposure of arterial wall to these processes → formation of atheromatous plaques
What is the step by step process of development of atheromatous plaques?
Endothelial injury
LDL accumulation in vessel wall
Monocyte adhesion to endothelium
Migration of monocytes to intima and transformation into foamy macrophages
Platelet adhesion
Activated platelets release factors causing macrophage recruitment to smooth muscle cell
Smooth muscle cell proliferation - extracellular matrix production and T-cell recruitment
Lipid accumulation (extracellular and in foamy macrophages)
What are the possible causes of atheromatous plaques?
- haemodynamic disturbances (turbulent flow)
- hypercholesterolaemia
(chronic hypercholesterolaemia increases production of reactive oxygen species)
(lipoproteins aggregate in intima and are modified by free radicals produced by inflammatory cells → modified LDL is gathered by macrophages but not completely degraded forming foamy macrophages → partly broken down LDL is toxic to endothelial cells plus release of growth factors, cytokines)
How are injured endothelial cells functionally altered?
Enhanced expression of cell adhesion molecules (ICAM-1, E-selectin)
•High permeability for LDL – normally LDL wouldn’t be able to cross barrier
Increased thrombogenicity
How do lipid laden macrophages die?
Through apoptosis - lipid into lipid core
What is the effect of PDGF? (Platelet derived growth factor)
Proliferation of intimal smooth muscle cells and subsequent synthesis of collagen, elastin and mucopolysaccharide
Where are growth factors secreted?
Platelets, injured endothelium, macrophages and smooth muscle cells
Where do microthrombi form?
Denuded area of the plaque surface
How are microthrombi organised?
Same repair process (smooth muscle cell invasion and collagen deposition) - repeated cycles eventually increase plaque volume
What is normally the level of occlusion resulting in •reversible tissue ischaemia
Stenosis of > 50-75% of vessel lumen → critical reduction of blood flow in distal arterial bed
What causes stable angina?
stenosed atheromatous coronary artery
What causes ischaemic pain at rest?
Very severe stenosis - unstable angina
What causes intermittant claudication?
ileal, femoral, popliteal artery stenosis
What is the effect of Longstanding tissue ischaemia?
•atrophy of affected organ e.g. atherosclerotic renal artery stenosis → renal atrophy
What are the immediate events following the rupture of a plaque?
•exposes highly thrombogenic plaque contents (collagen, lipid, debris) to blood stream → activation of coagulation cascade and thrombotic occlusion in very short time
What is the effect of total occlusion?
Irreversible ischaemia - necrosis (infarction of tissues)
- E.g. myocardial infarct (coronary artery)
- E.g. stroke (carotid, cerebral artery)
- E.g. lower limb gangrene (ileal, femoral, popliteal artery)
Where do detatchments of small thrombus fragments from thrombosed atheromatous arteries embolise?
Distal to the ruptured plaque
What is the result of emolic occlusion of small vessels?
- small infarcts in organs
- E.g. heart, dangerous small foci of necrosis → life-threatening arrhythmias
- E.g. large ulcerating aortic plaques, lipid rich fragments of plaque → cholesterol emboli in kidney, leg, skin
- E.g. carotid artery atheromatous debris, common cause stroke (cerebral infarct/TIA)
What causes an atheromatous abdominal aortic aneurysm?
Weakened media beneath atheromatous plaques - causing the gradual dilation of the vessel
What is the result of a ruptured abdominal aortic annyeurism?
- massive retroperitoneal haemorrhage (high mortality)
- Aneurysms > 5cm diameter at high risk of rupture
- Mural thrombus → emboli to legs
Define mural thrombus
A thrombus in a large blood vessel that decreases blood flow through that vessel
What plaques have a high risk of developing thrombitic complications?
•Typically thin fibrous cap, large lipid core, prominent inflammation
What is the effect of pronounced inflammatory activity?
Degradation and weakening of plaque
Increased risk of rupture
What do inflammatory cells release that increase the risk of rupture and cause degradation?
Secretion of proteolytic enzymes, cytokines and reactive oxygen species
Which plaques are less likely to rupture?
Highly stenotic plaques with large fibrocalcific component, little inflammation
What are the preventative and therapeutic options?
- Stop smoking
- Control blood pressure
- Weight-loss
- Regular exercise
- Dietary modifications
- Secondary prevention:
- Cholesterol lowering drugs, aspirin (inhibits platelet aggregation to decrease risk of thrombosis on established atheromatous plaques)
•
•Surgical options
