Myocardial Infarction (MI) L9.pdf

Myocardial infarction (MI) • Myocardial – heart muscle • ‘Infarction’ – death of tissue following lack of blood supply • Commonest cause of mortality and morbidity in adults. • MI aka coronary thrombosis Morbidity the condition of suffering from a disease or medical condition 1 The Heart’s Blood S...

Myocardial infarction (MI) • Myocardial – heart muscle • ‘Infarction’ – death of tissue following lack of blood supply • Commonest cause of mortality and morbidity in adults. • MI aka coronary thrombosis Morbidity the condition of suffering from a disease or medical condition 1 The Heart’s Blood Supply Tortora p 708 2 Coronary circulation Left coronary artery • CIRCUMFLEX BRANCH - left ventricle and left atrium • ANTERIOR INTERVENTRICULAR BRANCH - both ventricles. Right coronary artery • POSTERIOR INTERVENTRICULAR BRANCH –both ventricles • MARGINAL BRANCH –right ventricle • After entering capillaries, blood drains into coronary veins then CORONARY SINUS and empties into RIGHT ATRIUM 3 Artery structure Tortora p 739 4 Myocardial infarction (MI) (coronary thrombosis) Cause: supply of blood to coronary muscle reduced by a critical value - usually the result of atheromatous plaque rupture with overlying thrombosis What is ATHEROMA? 5 Atheroma development in Coronary Arteries https://basicmedicalkey.com/prophylaxis-of-atherosclerotic-cardiovascular-disease/ 6 Atheroma development in Coronary Arteries (2) https://basicmedicalkey.com/prophylaxis-of-atherosclerotic-cardiovascular-disease/ 7 Atheroma development in Coronary Arteries (3) https://basicmedicalkey.com/prophylaxis-of-atherosclerotic-cardiovascular-disease/ 8 Atheroma development in Coronary Arteries (4) https://basicmedicalkey.com/prophylaxis-of-atherosclerotic-cardiovascular-disease/ 9 Development of atheroma in coronary arteries • Cause: • Initial damage to endothelium in arteries (>2mm diameter). • Cholesterol-rich low density lipoproteins enter the intima and taken up by macrophages • Fat-laden macrophages (FOAM CELLS) underneath endothelial cells = FATTY STREAK • Macrophages release lipid (and chemical signals) into intima. • Cells of intima release collagen in response to signals. • Formation of a raised yellow smooth area = LIPID PLAQUE • Fibrolipid cap forms • Endothelium fragile and often ulcerates • Platelets aggregate on plaque which stimulates thrombus formation 10 Atheroma in segments of aorta • F = fatty streak (lipid-rich macrophages) • P = fibrolipid plaque • • (macrophages secrete cytokines causing collagen secretion) hard and white • T = ulcerated advanced plaque with thrombus 11 P159 Stevens, Lowe and Scott The consequences of atheroma 1. Artery narrowing - ischaemia, hypoxia, angina pectoris, pain 2. Thrombus formation on the plaque –MI 3. Bleeding into the plaque – can occur in coronary arteries - MI 4. Aneurysm p 161 Stevens, Lowe and Scott 12 Some definitions • Arteriosclerosis- thickening and hardening of artery wall • Atherosclerosis – thickening and hardening of high pressure artery wall caused by atheroma. • Atheroma – lipid-rich accumulation in arteries 13 Acute Myocardial Infarction (AMI) diagnosis • Altered level of cardiac muscle biomarker (preferably troponin) • Plus: • Crushing chest pain /ECG changes/ imaging evidence • ECG interpretation • http://www.amperordirect.com/pc/help-ecg-monitor/z-interpretingecg.html Ahmed, p188 (1st edition) p168 (2nd edition) 14 Diagnosis of MI- electrocardiogram (ECG) • Elevated ST region • May take 24 hours to develop and be difficult to interpret P54-55 Gaw, p714-5 Tortora 15 CARDIAC BIOMARKERS • ENZYMES • Creatine kinase (CKMB)– muscle damage, specificity issue • Lactate dehydrogenase (LDH) – (not since 2000) • Aspartate aminotransferase (AST) –(not since 2000) • MUSCLE PROTEINS • Myoglobin. Detectable 2-3 hours after MI, peak 12h. Specificity issue (also in skeletal muscle). • Troponin I (cTnI)– SPECIFIC for cardiac muscle • Troponin T (cTnT)– SPECIFIC for cardiac muscle P54 Gaw, p165-169 Ahmed 2nd ed. 16 Cardiac muscle structure P773 Tortora 17 Troponins • Exist as a complex with actin and myosin and regulates the contraction of striated muscle • 3 forms : • Troponin C: binds calcium – regulates the action of the filaments during contraction. • Troponin I: Inhibitory subunit – prevents contraction in the absence of calcium and Troponin C • Troponin T: binds the complex to tropomyosin • Troponins from different muscle types have different amino acid compositions • cTI, cTT, cTC – cardiac troponins 18 Calcium binding to Troponin C enables muscle contraction 19 Cardiac damage causes the release of cellular components into the bloodstream 20 Gold Standard MI Testing - Troponins • Main Lab Sample • POC Technology Treatment of MI • Thrombolytic agents • STREPTOKINASE • TISSUE PLASMINOGEN ACTIVATOR • Anticoagulant • HEPARIN 22 Treatment – Coronary angioplasty • Catheter inflated in obstructed vessel to remove obstruction and enable blood flow • Coronary angioplasty • http://www.youtube.com/watch?v=S9AqBd4RExk&NR=1 23 Treatment – Coronary bypass • Graft of artery or vein to coronary artery – enables blood to flow around the obstruction. • coronary bypass 2 • http://www.youtube.com/watch?v=GvGAgQOhQqY&feature=related 24