Vascular Diseases Flashcards
How does lipoprotein transport occur?
What are the 4 main types of lipoproteins?
- Lipoproteins are complexes of lipid (hydrophobic core) and apoprotein (hydrophilic coat)
- Lipids do not dissolve easily in aqueous solutions like blood and therefore must be packaged (by apoproteins)
- Lipoproteins allow the transport of triglycerides and cholesterol through blood
- There are 4 main types of lipoproteins (in decreasing size)
1. Chylomicrons (triglycerides)
2. Very low density lipoproteins- VLDL (triglycerides)
3. LDL (cholesterol) - can penetrate vascular endothelium
- form Lp(a) which contains Apo B-100 is similar to and competes with plasminogen
4. HDL (cholesterol) - can penetrate vascular endotheilum
- contain Apo-1-1 (protective)
Describe lipoprotein transport in the blood:
- Exogenous pathway:
- cholesterol/triglycerides derived from GIT
- move into intestinal lymph
- are transported as chylomicrons in the plasma
- are hydrolysed and then used by the muscle for energy or stored in adipose tissue - Endogenous pathway:
- cholesterol/triglycerides synthesised in the liver
- transported as VLDL into muscle/adipose tissue
- hydrolysed
- lipoprotein particles become LDL (which can morph into HDL)
How do HDLs and LDLs interact with the vascular smooth muscle cells?
LDLs:
- LDL receptors on hepatocytes and VSMCs allow for the receptor mediated endocytosis of LDL via apo-b-100
- Therefore LDL is strongly correlated with atherosclerosis and CHD: LDL forms plaques and Lp(a) reduces plasminogen activity and favours thrombosis
HDLs:
- HDLs cause reverse cholesterol transport
- HDL does not have apo-b-100 so is not incorporated into cells, instead it removes excess cholesterol from cells and incorporates it via the ApoA-1
- HDL acts as a resevoir to revere and remove cholesterol out of target tissues
- HDL has a cardioprotective effect and is associated with reduced atherosclerosis and CVD
Describe the mechanism of atherosclerotic plaque formation:
- Vascular Inflammation:
- Leukocytes are captured, adhere and migrate into the subendothelial space
- The infiltration of the leukocytes and the subsequent inflammation triggers the atherosclerotic process - Vascular cholesterol uptake by LDL receptors:
- Excess LDL infiltrates the artery
- Oxidised LDL induces adhesion molecule expression on endothelium
- Oxidised LDL is phagocytosed by vascular macrophages (now called foam cells) - Monocyte recruitment into arterial wall:
- Adhesion molecules facilitate the entry of monocytes into the vascular tissue
- The monocytes differentiate into macrophages
- The macrophages release pro-inflammatory mediators and create a local inflammatory milieu which contributes to CVD - Immune cell surveillance:
- T cells infiltrate
- The activated T-cells produce Th1 cytokines (IFNy, IL-1, IL-6, TNF)
- Results in an amplification of vascular inflammation - There is then the formation of a fibrous cap on the plaque creating a fibrous plaque
What is CRP?
- C-reactive protein (CRP) is an acute phase protein synthesised in the liver
- It is stimulated by IL-6 from inflammatory cells and binds to the surface of dying cells and promotes phagocytosis
- It is predictive of inflammation/CVD and informs on statin therapy
Why is outward (non-stenotic) remodeling more likely to be associated with unexpected cardiac failure?
- Non-sentonic lesions are typically more ‘mild’ angiographically as they occlude the arteries to a lesser extent
- These lesions however have a much thinner fibrous cap is much more prone to rupture which can cause abrupt cardiac failure as plaque rupture will often precede a thromobsis as the plaque contents adhere to the endothelial surface and coagulate cells leading to thrombus formation
- When there is a break in the endothelial layer e.g. a plaque rupture, platelets readily attach and release mediators leading to further platelet aggregation and coagulation
- These factors cause the formation of an insoluble fibrin clot
What makes a plaque vulnerable to rupture?
- Decreased collagen synthesis (T cell driven)
- Increased degradation of the fibrous cap due to MMPs released from macrophages
- Increased tissue factor released from macrophages
How are acute life-threatening cardiovascular events treated?
- Revascularisation:
- Pericutaneous coronary intervention (PCI)/angioplasty
- Usually with stents
- A coronary artery bypas graft is also commonly used to bypass the occluded vessel - Drugs:
- t-PA (narrow window of effect- 12 hours for a MI and 4 hours for a stroke)
- activates plasminogen into plasmin which dissolves the clot
How are chronic issues with artherosclerosis treated?
- Lipid-lowering drugs
- statins - Anti-platelet drugs
- Anti-coagulant drugs
- Other drugs to reduce CHD burden
What is hyperlipidaemia?
Primary:
- A combination of high cholesterol (hypercholesterolaemia) and/or high triglycerides (hypertriglyceridaemia)
- Caused by genetics e.g. FH (defective LDL receptor) or dietary excess
Secondary (to another disease):
e.g. diabetes, alcoholism, obstructive liver disease, drugs
How do statins work?
- Statins are HMG-CoA reductase inhibitors
- Therefore these drugs stop the endogenous formation of cholesterol in hepatocytes
- This promotes increased expression of LDL receptors (by feedback regulation) which then increases LDL plasma clearance
- Therefore they help lower LDL and TG, and increase HDL
- Statins are extremely effective and used as a primary prevention against CVD and secondary prevention of MI and stroke
- Has only mild side effects (GI disturbance, insomnia, rash)
- Reduced CRP levels indicate effective therapy
How do PCSK9 inhibitors work?
- PCSK9 is a circulating serine protease that binds to LDL receptors and facilitates their lysosomal degradation and thus reduces LDL receptor recycling to the surface of cells
- Inhibiting this enzyme (as a novel therapy) has the potential to prevent PCSK9 from binding LDL receptors and promoting the expression of LDL receptors on the surface of hepatocytes
- This will help increase plasma clearance of LDL and this LDL can then be converted into HDL by the hepatocyte
- The current inhibitors are antibodies (biologics) meaning they are not orally active but instead must be administered via intramuscular injections
- Could be used in patients that do not respond well to statins
What are acute vs. chronic presentations of coronary heart disease?
Acute presentation:
- Acute coronary syndrome
- Angina with radiating chet pain
- Acute MI
Chronic disease:
- Stable angina
- Heart failure
Why is the sub-endocardial zone so vulnerable to ischaemia?
- The coronary arteries are external to the myocardium and are embedded in a layer of fat- they then branch into the myocardium
- The sub-endocardial zone oxygen supply is a balance of coronary supply vs diffusion from LV
Describe the acute coronary syndrome continuum:
- The ACS continuum goes from normal -> angina -> ACS (any condition causing sudden, reduced blood flow to the heart) which falls into 2 categories which both show CK elevations:
1. no ST-segment elevation MI (NSTEMI) which is less severe
2. ST-segment elevation MI (STEMI): usually more severe infarcts
What is angina pectoris?
- Severe, crushing chest pain and potentially shortness of breath
- Due to an imbalance in mycardial O2 demand»_space; O2 supply
- There are 3 main types:
1. Chronic, stable angina: - caused by ‘demand’ e.g. exercise, stress-test etc.
2. Unstable angina: - unpredictable, thrombi formation, may not resolve in a few minutes, classic ACS
3. Variant angina: - spasm of the coronary artery
- no artherosclerosis
How is angina pectoris treated?
- Acute relief by rest and/or nitro-vasodilators
- Prevention by nitro-vasodilators, B1 adrenoreceptor antagonist, calcium channel antagonists (stable angina)
- The main aim is to increase coronary artery perfusion to increase oxygen supply and reduce the metabolic demand of the heart muscle
How do nitro-vasodilators treat angina?
- Nitric oxide is produced in endothelial cells and then enters the VSMC and activates the guanylyl cyclase system creating cGML which offsets the contraction of the smooth muscle causing a relaxing and vasodilatory effect
- Glyceryl trinatrate (GTN) can be used as a treatment for angina by providing an additional exogenous source of NO
- The venous dilation reduces venous pressure and pre-load which then causes a decrease in cardiac oxygen consumption
- The arteriolar dilation reduces peripheral vascular resistance and after-load which then causes a decrease in cardiac oxygen consumption
- Only acts on smooth muscle (no effect on cardiac or skeletal muscle)
What are the limitations of using nitro-vasodilators?
- Can cause hypotension therefore should not be combined with viagra or other drugs (which inhibit PDE and thus prevents breakdown of cGMP)
- Hypotension can cause fainting, reflex tachycardia, headaches and flushing
- After continous exposure to nitrates a tolerance may develop (which must be offset by nitrate-free periods between transdermal patches)
What is an acute mycordial infarction?
- Defined as cardiomyocyte necrosis in a clinical setting consistent with acute myocardial ischaemia
- For there to be the diagnosis of an acute MI there must be:
1. Symptoms of ischaemia
2. New/presumed new changes in ST-T wave or left bundle block on ECG
3. Development of pathological Q waves on ECG
4. Imagining evidence of new or presumed new loss of viable myocardium
5. Intracoronary thrombus detected
What cardiac biomarkers indicate an acute myocardial infarction?
- Elevated cardiac troponin (cTn)
- Gold standard
- Detected 4-10 hours after MI (peak at 12-48)
- Larger window to detect
- Cardiac specific - Elevated myoglobin:
- Released into blood after AMI (1-2 hours)
- Also detected after skeletal muscle injury - Elevated creatine kinase:
- Detected in blood after an AMI or skeletal muscle injury
- CK-MB is considered relatively heart specific
What are the causes of acute myocardial infarction?
- Coronary artery occlusion (atheroma)
- Aortic valve problems
- Coronary artery aneurysms
- Arrhythmia
- Cocaine/methamphetamines
- Chemotherapy
- Hypertension
- Diabetes
What is the time-course of outcomes after an MI?
- There can be sudden death due to electrical/mechanical pump failure (within hours)
- Arrythmias (first few days)
- Pain (within days)
- Angina (immediate or delayed)
- Cardiac failure (variable to chronic state)
- Mitral incompetence (variable)
- Pericarditis (2-4 days)
- Cardiac rupture (0-5+ days as tissue is the weakest)
- Mural thrombosis (1+ weeks)
- Ventricular aneurysm (4+ weeks)
- Further infarction (variable)
What is acute vs chronic heart failure?
Acute heart failure:
- Precipitated by an event e.g. trauma or AMI
- Can progress into chronic heart failure
Chronic heart failure:
- Persistant cardiac injury that occurs over decases
- There are 2 main kinds:
1. Systolic dysfunction (impaired contraction, reduced ejection fraction- now called HF with reduced rejection fraction)
2. Diastolic dysfunction (contraction okay but filling impaired, now called HF with preserved ejection fraction) - People with stable chronic heart failure can have an acute heart failure inducing event
How do different forms of ventricular remodelling affect the type of chronic heart failure that develops?
Systolic heart failure:
- Dilated cardiomyopathy (thin ventricular walls)
- Reduced cardiac output (ejection fraction)
- Reduced EF
Diastolic heart failure:
- Thickening of the ventricles
- Ventricle relaxation and filling reduced
- CO preserved with rest but reduced with exercise
- Normal EF
How does a myocardial infarct evolve and change in structure?
- There is a concept of reparative and reactive fibrosis
- This means that not only does fibrous tissue replace the necrotic region, there is also fibrous spillover into non-infarcted tissue (due to local inflammation and oxidative stress)
- This fibrous spilloever impairs contraction of the heart
What is congestive heart failure?
- Congestive heart failure is a reduction in the cardiac output to a point where it is unable to meet the metabolic demands of the body
- It is the result of progressive ventricular dysfunction
- There are many different causes including: coronary heart disease, atheroscleoris, AMI, ischaemia, angina, hypertension etc.
- It causes a wide range of symptoms and levels of impairment (how much activity is limited by dyspnea)
- It is treated with lifestyle changes such as weight loss, reduction in sodium and exercise and well as drugs to decrease cardiac workload such as angiotensin inhibition, B-blockers and diuretics
What are the most common drugs used to treat heart failure and hypertension?
A: angiotensin converting enzyme (ACE) inhibitors and angiotensin atagonists
B: beta blockers
C: calcium channel blockers (not for heart failure, only hypertension)
D: diuretics (thiazides, loop, K+ sparing)
What is angiotensin II?
- Angiotensin II is a hormone that is part of the RAAS system that is important in the long-term control of BP
- It has peripheral effects such as vasoconstriction, aldoesterone release (increased Na+ absorption), increased noradrenaline release and upregulation of fibrosis, hypertrophy and oxidative stress
- Its central effects include upregulated BP, increased vasopressin release
- Angiotensin II is upregulated to raise MAP in response to reduced cardiac output, this causes increased vasoconstriction and thus worsens the cardiac state (as the heart must pump harder to overcome the resistance)
What are angiotensin converting enzyme inhibitors and how do they work?
- ACE inhibitors block the conversion of angiotensin I into angiotensin II
- This helps reduce BP as angiotensin raises BP via a number of mechanisms (vasoconstriction, sodium reaborption, noradrenaline release)
- ACE inhibitors also inhibit bradykinin breakdown (ACE = kininase II): bradykinin is a local inflammatory mediator that has a marked local vasodilatory effect (but is also an irritant)
- The overall effects of this are: reduced peripheral resistance (due to vasodilation) and increased sodium and water excretion (reduces BP)
- The drug is therefore used to treat hypertension, heart failure (and to prevent diabetic vascular complications)