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Ischaemic Heart Disease (Angina Pectoris (Risk Factors (Diabetes,…
Ischaemic Heart Disease
Atherosclerosis
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Distribution
Circumflex, left anterior descending and right coronary arteries commonly develop atherosclerosis
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Pathogenesis
Inflammatory cytokines found in the plaques: IL-1, IL-6, IFN-gamma
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Chemoattractants are released from the endothelium to attract leukocytes which then accumulate and migrate into the vessel wall
Excessive inflammation causes myocardial reperfusion injury, atherosclerosis, IHD, RA, asthma, IBS, shock, excessive wound healing
Endothelial cells are injured by modified LDL. The LDL undergoes oxidation and glycation, causing endothelial dysfunction
Fatty streaks are the earliest lesion of atherosclerosis - they are made up of lipid-laden macrophages (foam cells) and T cells
Intermediate lesions are composed of foam cells and T cells. They adhere and aggregate platelets to the vessel wall
Advanced lesions impede blood flow. They are covered by a dense fibrous cap made of collagen and elastin.
Fibrous cap on advanced lesion can become weak and rupture. There is haemorrhage of vessels, collagen and basement membrane. There is thrombus formation and vessel occlusion
If fibrous cap does not rupture, the plaque can erode the vessel and still cause thrombosis
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Angina Pectoris
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Pathophysiology
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Mismatch is caused by: impairment of blood flow by arterial stenosis, increased distal resistance e.g. LV hypertrophy, reduced oxygen carrying capacity of blood i.e. anaemia, reduction in blood vessel diameter
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In IHD, epicardial artery resistance is high due to stenosis. Microvascular vessel resistance falls to compensate, however there is a point where it cannot fall any lower. Flow cannot meet metabolic demand. Myocardium becomes ischaemic and pain occurs. Only way to reverse is to rest.
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Features of Angina
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Heavy/constricting pain to chest, jaw, neck, shoulders or arms
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Types
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Prinzmetal Angina - Caused by coronary artery spasm, rare
Unstable Angina - Angina of increasing frequency or severity. Occurs on minimal exertion. Associated with high risk of MI
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Stable Angina - induced by effort, relieved by rest. Good prognosis
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Investigations
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Exercise stress treadmill test - patient is wired to ECG whilst on treadmill and asked to walk uphill incrementally faster till they cannot go any further. Look for ST depression. Many patients will not be able to do this test due to being unfit
CT Angiography - CT scan of coronary arteries to look for calcium (more calcium the more plaques), has low positive predictive value
Stress echo - dynamic imaging, looks at heart function under stress
Echocardiogram - checks LV function, shows signs of previous infarcts
SPECT - nuclear perfusion test, radio-labelled tracer is taken up by metabolising tissues to detect blood supply
12 Lead ECG - look for ST depression, inverted T wave, BBB
Treatment
Beta Blockers
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Examples: bisoprolol, atenolol
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Side effects: bradycardia, erectile dysfunction, cold hands and feet, fatigue
Contraindications: Asthma, bronchospasm, severe heart block, Prinzmetal's angina
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Aspirin 75mg daily - inhibits platelet aggregation and inhibits COX, reducing prostaglandin synthesis
Calcium Channel Blocker
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Examples: Verapamil, amlodipine
Modify risk factors: stop smoking, exercise, lose weight
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Acute Coronary Syndrome
Definitions
Ischaemia = Lack of blood supply, can cause cell death
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Myocardial Infarction = Myocardial cell death, releasing troponin
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ACS = Umbrella term that includes STEMI, unstable angina and NSTEMI
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Myocardial Infarction
NSTEMI: Complete occlusion of a minor coronary artery OR a partial occlusion of a major coronary artery. ST depression, T wave inversion, no Q wave
To distinguish between unstable angina and NSTEMI, look at troponin levels - a rise in troponin indicates NSTEMI
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Symptoms: Chest pain, occurs at rest, sweating, breathlessness, nausea
STEMI: complete occlusion of a major coronary artery causes full thickness damage of heart muscle. ST elevation and pathological Q wave
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Management: 999, 300mg aspirin immediately, morphine, nitrates, oxygen only if hypoxic, bed rest, urgent coronary angiography, beta blocker
Risk Factors: Age, male, family history, smoking, hypertension, obesity
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Aetiology
Drug abuse with cocaine, amphetamine
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Troponin
Troponin rise is not specific for ACS. Can also indicate sepsis, renal failure and pulmonary embolism
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Troponin is a highly sensitive marker for cardiac muscle injury as when cardiac muscle is injured, troponin is released
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Investigations
Measure troponin levels, CK-MB rise, myoglobin levels
Chest x-ray: look for cardiomegaly, pulmonary oedema, widened mediastinum
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Treatment
Modify risk factors
Treat diabetes, hypertension, hyperlipidaemia
Advise diet high in oily fish, fruit, veg, fibre, low in saturated fats
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Drugs
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Glycoprotein IIb/IIa antagonist - IV, increases risk of major bleeding
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