Cardiology Flashcards
What is atherosclerosis?
Inflammatory process characterised by hardened plaques within the intima of a vessel wall. Eventually, plaque will either occlude vessel lumen resulting in a restriction of blood flow (angina) or rupture (thrombus formation - death).
Where do atherosclerotic plaques often occur?
Peripheral and Coronary arteries!
How are atherosclerotic plaques distributed in these arteries?
Focally distributed - governed by haemodynamic factors. For example, changes in flow/ turbulence (e.g. bifurcations)
What is neointima?
As the intima grows (new intima)
Changes in blood flow altering the phenotype of endothelial cells.
Altered gene expression in key; endothelial cells, smooth muscle cells, macrophages and fibroblasts
What makes up the structure of an atherosclerotic plaque?
Lipid
Necrotic core
Connective tissue
Fibrous cap
Lymphocytes
What are the 5 main stages of atherosclerosis progression over the course of the condition?
Fatty Streak
Intermediate Lesions
Fibrous Plaques (advanced lesions)
Plaque Rupture
Plaque Erosion
What is the fatty streak stage of atherosclerosis?
Earliest lesion of atherosclerosis < 10 years:
- Scavenger receptors take up lipids in intima layer of vessel wall
- Aggregations of lipid-laden macrophages (Foam Cells) and T lymphocytes within the intima layer of the vessel wall.
What is the intermediate lesion stage of atherosclerosis?
Lesion progresses to comprise layers of;
Foam cells
Vascular smooth muscle cells
T lymphocytes
Adhesion and aggregation of platelets to vessel walls
Extracellular Lipid Pools
What is the fibrous plaque stage of atherosclerosis?
- Contains SMCs, macrophages, foam cell and T-lymphocytes
- Covered by dense fibrous caps made of ECM proteins including; collagen (strength), elastin (flexibility) - these are laid down by SMCs
- Impedes blood flow and prone to rupture
- Often calcified
What is the plaque rupture stage of atherosclerosis?
Why might atherosclerotic plaques Rupture?
- Plaque is constantly growing and receding - fibrous cap has to be resorbed and redeposited in order to be maintained
- If balance shifted in favour inflammatory conditions (e.g. increased enzyme activity) the cap becomes weak and plaque ruptures.
- Exposure of basement membrane, collagen, necrotic tissue and haemorrhage of vessels within plaque causes thrombus formation and vessel occlusion
What is the plaque erosion stage of atherosclerosis?
- Small early lesions
- Fibrous cap does not disrupt
- Luminal surface underneath the clot may not have enough endothelium present but is smooth muscle rich
- Prominent lipid core
What are the stages of atherosclerotic plaque formation?
1️⃣ Initiation of inflammation and endothelial cell dysfunction
2️⃣ Stimulus for adhesion of leukocytes - release of chemo-attractants
3️⃣ Dysfunctional endothelial cells allow the transmigration of LDLs into the tunica intima
4️⃣ Accumulation of LDLs tunica intima cause dysfuntional endothelial cells to release ROS and metalloproteases which function to oxidised the LDL → activated oxLDL
5️⃣ The activation of oxLDLs causes endothelial cells to express adhesion receptors for leukcocytes on their surface, leading to uptake of LDLs and monocytes
6️⃣ Surface of macrophages contain a scavenger receptor which facilitates the uptake of oxidised LDLs to form a foam cells
7️⃣ Foam cells have multiple pathophysiological functions:
- Release chemokines to attract more macrophages
- Release IGF-1 into tunica media to promote migration of SMCs (from media to intima) that increase collagen synthesis leading to the hardening of the atherosclerotic plaque
8️⃣ During this process, foam cells will die → releasing lipid content. This drives the growth of the plaque
9️⃣ Death of foam cells also causes release of contents which causes increased inflammation
🔟 T-cells also facilitate inflammation
🔟+ Excessive growth of the plaque causes it to rupture, leading to accumulation of the RBC, platelets and clotting factors → thrombosis
What initiates inflammation and leads to endothelial cell dysfunction in atherosclerosis?
Cholesterol/ high LDLs in the blood damages the endothelial cells
ROS from inflammation.
What chemo attractant is released by the endothelium and what does this lead to?
Selectins cause leukocyte rolling and firm adhesion to the blood vessel walls.
What are the pathological functions of a foam cell?
Release chemokines and attract further macrophages to the tunica intima
Release IGF-1 into the tunica media to promote migration of Smooth muscle cells from the tunica media into the tunica intima which increases the collagen synthesis and leads to the hardening of the atherosclerotic plaque.
What is a foam cell?
A macrophage that has been up take into the tunica intima that expresses scavenger receptors that will uptake oxidised LDLs
This uptake forms a foam cell.
What is a foam cell?
A macrophage that has been up take into the tunica intima that expresses scavenger receptors that will uptake oxidised LDLs
This uptake forms a foam cell.
What does the death of the foam cell release in atherosclerosis?
DNA material that attracts neutrophils
Proinflammatory cytokines
ROS
These all lead to increased inflammation.
What inflammatory cytokines are found in atherosclerotic plaques?
- IL1, 6 and 8.
- IFN-γ - strong proinflammatory cytokine
- TGF-β - involves in wound healing
- Chemokines (e.g. Monocyte Chemoattractant Protein-1)
How can Atherosclerosis (Coronary Heart Disease) be treated?
Percutaneous Coronary Intervention
Drugs
What is Percutaneous Coronary Intervention?
Non-surgical procedure that uses a catheter to place a stent into a narrowed blood vessel
What is Re-stenosis?
The recurrence of abnormal narrowing of an artery or valve after corrective therapy
What drugs are used to reduce restenosis in patients who have undergone corrective surgery?
Taxol and Sirolimus - work by reducing SMC proliferation after placement of stent. The stent is washed (eluted) with these drugs
How does Aspirin help to treat CHD?
Irreversible inhibitor of platelet cyclo-oxygenase to prevent Thromboxane A2 production and further platelet aggregation