Cardiovascular Disease Flashcards
What is occurring during systole?
contraction and emptying of chambers
What is occuring in diastole?
relaxation and filling of chambers
Describe the action potential occuring in the pacemaker cells in the heart (sinoatrial node).
- Cells are autorhythmic
- Cells can initiate and conduct action potentials (self-induced)
- Has no resting membrane potential, constantly firing
- Cells slowly drift towards the threshold (~40mV)
- Sodium induces the action potential (positive charge crossing membrane starts a slow depolarisation)
- Calcium rushes into the cell which causes rapid depolarisation. The L-type calcium channels will then close when the peak is reached.
- Repolarisation is initiated by potassium leaving the cell through rectifier channels.
- This action potential uses: L-type channels (VGCC), T-type channels (VGCC), funny channels (Na) and rectifier channels (K).
Describe the action potential occuring in the cardiomyocyte cells.
- Cells have a resting membrane potential, so are not autorhythmic (~70mV)
- Cardiomyocytes only use L-type VGCCs
- Sodium influx induces the action potential. Permeability for sodium increases causing rapid depolarisation.
- At the peak of the action potential, sodium permeability decreases and potassium permeability is increased allowing for it to leave the cell, which initiates slow repolarisation.
- Shortly after, L-type channels open allowing Calcium in slowly which causes a plateau.
- Then the calcium channels shut and potassium leaves the cell rapidly through rectifier channels again causing repolarisation back to the resting potential.
How have each cardiac cell type adapted to fit its function?
- The pacemaker cells in the sinoatrial node have adapted to allow for autorhythmicity, which allows for constant firing of the action potential.
- The cardiomyocyte has adapted to allow calcium inside the cell during the action potential which allows the muscle cell to contract to push blood out of the heart.
What lifestyle advice can be offered to patients as part of primary prevention?
- behaviour change
- healthy eating
- cardioprotective diet
- physical activity
- weight management
- alcohol and smoking
Primary prevention of CVD for people with/without Type 2 DM
- If QRISK3 >= 10%, offer Atorvastatin 20mg daily
Primary prevention of CVD for people with Type 1 DM
- Offer 20mg Atorvastatin daily
- Offer when: >40y/o, DM for >= 10yrs, establiashed nephropathy, other CVD risk factors
Secondary prevention (after CV event) for people with/without Type 1 or 2 DM
- Offer 80mg Atorvastatin daily
Primary AND secondary prevention for people with CKD
- Offer 20mg Atorvastatin daily
- If eGFR is >30, dose increase? (renal specialist)
What are the side effects of statin therapy?
- statin related muscle toxicity (SRM) - elevated creatine kinase, symmetrical muscle pain and/or weakness, large proximal muscles
- GI disturbances, hepatotoxicity, new onset Type 2 DM, intercranial haemorrhage, sleep disturbance
What can be done for intolerance to statins?
- De-challenge (reduce dose)
- Re-challenge
- Change statin (hydrophilic = Rosuvastatin, lipophilic = Atorvastatin)
- Alternate days dosing
- Alternate drug (Ezetimibe, PCSK9i, Inclisiran)
How are fibrates chemically activated in the body?
They are a pro-drug, and the ester group needs to be cleaved before it can be active. The active species has a carboxylic acid group.
Describe the mechanism of action of bile acid sequestrants.
- The drug itself is a chemical drug - it has no biological target.
- When the patient takes the sequestrant, it travels to the gut where bile acid emulsifies fat, and exchanges anions with the bile acid. In most circumstances, Cl- is exhanged for OH-. The polymer is then excreted with the bile acid attached to it.
- Increased excretion of bile acids means increased bile acids synthesised from cholesterol meaning reduced overall cholesterol levels.
Describe the mechanism of action of statins.
- competitive, reversible inhibition of HMG-CoA reductase.
- the enzyme itself is responsible for the inhibition of an early rate-limiting step in cholesterol biosynthesis, the conversion of HMG-CoA to mevalonate (mevalonic acid).
- as well as this, due to reduced levels of cholesterol in the liver lead to an increased upregulation of LDL receptors in the liver, which lead to increased hepatic uptake of cholesterol.
Why is Aspirin effective as an anti-platelet drug?
- Aspirin inhibits COX-1 irreversibly
- This means that thromboxane A2 and prostacyclin will both not be formed.
- Prostacyclin (PGI2) is an inhibitor of platelet aggregation and can be resynthesised in endothelial cells, whereas thrombxane A2 requires new COX regeneration.
- If thromboxane A2 is inhibited for longer than prostacyclin, this means that at a low dose Aspirin can act as an anti-platelet drug.
Describe the mechanism of action of Clopidogrel.
- it is an irreversible antagonist of the P2Y12 subtype of the ADP receptor found on platelets. This antagonistic effect prevents ADP from binding and activating platlet aggregation.
- undergoes in vivo metabolism into active species
- once activated, thiol can form disulphide bond with receptor
Describe the different classes of cholesterol.
- VLDL, IDL, LDL and chylomicrons - bad cholesterol
- HDL - good cholesterol
What apoprotein is found on chylomicrons?
B48 (A,C,E)
What apoprotein is found on VLDL?
B100 (A,C,E)
What apoprotein is found on IDL?
B100, E
What apoprotein is found on LDL?
B100
What apoprotein is found on HDL?
AI, AII (C,E)
What are each of the different lipoprotein classes responsible for?
- chylomicrons - lipid transport from gut
- VLDL, IDL, LDL - transport triglycerides and deposit glycerol and fatty acids in cells
- HDL - reverse cholesterol transport
What pathways are associated with endogenous lipids?
- Cholesterol (from diet and liver) and newly synthesised TGs travel as VLDL to muscle and adipose tissue
- TGs hydrolysed by lipase in tissues, fatty acids and glycerol are liberated.
- Lipoprotein particles become smaller but retain cholesteryl esters and become LDL, which binds to LDL receptors on hepatocytes (LDL receptors recognise ApoB100 on LDL particles)
- Cholesterol deposited in tissues for cell membranes and other functions
- Cholesterol can return to plasma and liver for tissues via HDL (reverse cholesterol transport)
- Cholesterl esterified with long chain fatty acids in HDL and transferred to VLDL or LDL in plasma by cholesteryl ester transfer protein (CETP).
Describe the LDL receptor pathway.
- LDL approaches the liver hepatocyte and binds to LDL receptor, which initiates receptor mediated endocytosis.
- The LDL and its receptor are taken up into a coated vesicle. This then starts to dissociate the LDL from the receptor. There is also a pH drop from 7 to 5.
- The vesicle then splits in two smaller vesicles, one containing the LDL and the other containing the receptor.
- The vesicle containing the LDL combines with a lysosome. Enzymes from the lysosome cause the release of cholesterol into the cytosol.
- The vesicle containing the receptor recycles it back onto the cell surafce via exocytosis.
Describe the pathway of reverse cholesterol transport.
- HDL is assembled in the liver and intestine (pre-βHDL).
- HDL acquires cholesterol from cell membranes in the peripheries via the ABCA1 transporter (ATP-binding casette transporter A1).
- Cholesterol acquired by HDL is esterified by lecithin cholesterol acyltransferase (LCAT)
- The cholesteryl esters move into the interior of the HDL particle which enlarges it, making it spherical - it is now HDL-3.
- Cholesteryl ester transfer protein (CETP) aids the transfer of cholesteryl esters to chylomicrons, VLDL and remnant particles in exchange for triglycerides.
- The acquisition enlarges the HDL again into HDL-2.
- Cholesterol remaining in the HDL-2 can be carried to the liver. There, HDL-2 can bind to scavenger receptor B1 and transfers cholesterol to the cell membrane.
Describe the enzymes involved with lipid transport.
- ACAT-acyl-CoA (cholesterol acyltransferase) - catalyses intracellular synthesis of cholesteryl esters in macrophages, adrneal cortex, gut and liver
- LCAT (lecithin cholesterol acyl transferase - catalyses cholesteryl ester synthesis in HDL particles
- CETP (cholesteryl ester transfer protein) - transfer of cholesteryl esters between HDL to LDL or VLDL
- PLTP (phospholipid transfer protein) - transfer of triglycerides and cholesterol between different classes of lipoproteins in plasma
Describe the aeitology of primary and secondary dyslipidaemia.
- Primary - combination of diet and genetics
- Secondary - underlying cause (disease or certain drug)
Describe the stages of Atherosclerosis.
- Injury occurs to endothelial cells (High BP, smoking, high cholsterol)
- Adhesion molecules come to surface and monocytes bind to endothelial cells
- LDL becomes oxidised and bind to adhesion molecules and monocytes leading to formation of foam cells
- Foam cells stick to the blood vessels underneath endothelial cells. This causes the smooth muscle to move, reducing the diameter of the artery.
- Plaque forms, blocking the flow of blood
- A necrotic core forms as there is a hypoxic and nutrient-deficient area in the build up
- Fibrous cap over build up can thin and eventually rupture causing myocardial infarction and/or stroke
Why is Lipoprotein A considered a risk factor?
- LDL is stronlgy associated with Atherosclerosis
- Locaslised to atherosclerotic lesions
- Apo(A) - structurally similar to plasminogen
- Lipoprotein(A) inhibits binding of plasminogen to receptorrs on endothelial cells - leads to less plasmin generation and promotiom of thrombosis
Describe the mechanism of action of the fibrates.
- Agonists for PPARalpha - subfamily of nuclear receptors that modulate lipid and carbohydrate metabolism and induce differentiation of different adipocytes (lipase - breakdown of VLDL and ApoA1 and ApoA5 - increased HDL production)
- Increased hepatic uptake of LDL
- Increased fatty acid uptake and synthesis of acyl CoA, therefore less fatty acids for TG synthesis
Describe the mechanism of action of Ezetimibe.
- Blocks cholesterol absorption, without affecting absorption of fat-soluble vitamins, TGs or bile acids
- Acts on NCPC1L1 in brush border enterocytes which is responsible, in part, for cholesterol absorption in the GI tract
Describe the mechanism of action of Alirocumab and Evolocumab
- They are mAbs that target proprotein convertase subtilisin/kexin type-9 (PCSK9).
- By doing this, they can increase receptor number and decrease LDL uptake into hepatocytes.
- By binding to receptors, they can force lysosomal degradation which prevents uptake of LDL from the blood
Describe the mechansim of action of Inclisiran.
Inclisiran is an siRNA treatment that inhibits translation of PCSK9 mRNA (gene silencing).
1. Ga1NaC targets Inclisiran to the heptatocyte ASGP receptor.
2. Endosomal uptake occurs, Ga1NaC cleaved, ASGPR recycled to cell membrane
3. Inclisiran slowly released from endosomes, resulting in sustained therapeutic effect
4. Inclisiran enters the RNA-induced silencing complex (RISC)
5. Inclisiran sense and anti-sense strands separate
6. Inclisiran anti-sense strand directs RISC to bind PCSK9 mRNA strands, triggering catayltic cleavage and reducing production of PCSK9.
7. Reduced PCSK9 results in increased LDL receptor recycling to the hepatocyte surface and increased clearance of circulating LDL.
Describe the mechanism of platelet adhesion, activation and secretion.
- Endothelial cells exposed to damage, platelets become activated by ADP and TXA2.
- Basement membrane becomes exposed to ECM (collagen and Von-Willebrand factor) - they combine and induce platelet aggregation
- Platelet aggregation causes platelet activation. Fibrinogen binds to glycoprotein IIb/IIIa receptors on platelet, forming links between platelets causing aggregation.
Describe the mechanism of action of Ticagrelor.
- blocks P2Y12 ADP receptors on platelets
- acts at a different binding site to ADP so allosterically inhibits
- blockage is reversible
Describe the mechanism of action of glycoprotein IIb/IIIa receptor antagonists.
Inhibits all pathways of platelet activation because drug binds to GP IIb/IIIa receptors, blocking fibrinogen which inhibits aggregation of platelet
Describe the role of thrombin.
- Thrombin cleaves fibrinogen, producing fragments that polymerise to form insoluble fibrin
- Activated factor XIII (stabilising factor) - strengthens fibrin links
What three things can initiate the intrinsic pathway of the coagulation cascade?
collagen, kallikrein, kininogen act on factor XII (hageman factor)