Myocardial Infarction

1. Myocardial Infarction Dr Isazadehfar

2. Background Myocardial Infarction is the rapid development of myocardial necrosis by a critical imbalance between oxygen supply and demand to the myocardium

3. Classification • Acute coronary syndromes include ST-elevation MI (STEMI) Non ST-elevation MI ( NSTEMI) Unstable Angina • Cardiac markers in circulation indicates myocardial infarction and help categorize MI and is a useful adjunct to diagnosis

4. Classification • Anatomic or morphologic Transmural= Full thickness Non- transmural= Partial thickness • ECG Q wave MI Non Q wave MI Does not distinguish transmural from a non- transmural MI as determined by pathology

5. Prevalence • Increase in the proportion of NSTEMI compared to STEMI

6. History The history is critical in making the diagnosis of MI and sometimes provide only the only clues that lead to the diagnosis in the initial phase of presentation

7. History • Chest Pain- anterior precordium tightness • Pain may radiate to jaw, neck and epigastrium • Dyspnea - angina equivalent, poor LV function • Nausea/abdominal pain with posterior MI • Anxiety

8. History • Nausea with and without vomiting • Diaphoresis or sweating • Syncope or near syncope • Elderly present with MS changes, fatigue, syncope or weakness • As many as half of MI are clinically silent

9. Physical exam • The physical exam can often be unremarkable • Hypertension • Hypotension • Acute valvular dysfunction may be present • Rales • Neck vein distention

10. Physical • Third heart sound may be present • A fourth heart sound poor LV compliance • Dysrhythmias • Low grade fever

11. Causes • Most frequent cause is rupture of an atherosclerotic lesion within coronary wall with subsequent spasm and thrombus formation • Coronary artery vasospasm • Ventricular hypertrophy • Hypoxia • Coronary artery emboli

12. Causes • Cocaine • Coronary anomalies • Aortic dissection • Pediatrics Kawasaki disease, Takayasu arteritis • Increased afterload which increases myocardial demand

13. Risk factors for atherosclerosis • Age • Male gender • Smoking • Hypercholesterolemia and triglyceridemia • Diabetes Mellitus • Poorly controlled hypertension • Type A personality

14. Risk factors for atherosclerosis • Family History • Sedentary lifestyle

15. Differentials • Acute coronary syndrome • Anxiety • Aortic stenosis • Asthma • Cholecystitis and biliary colic • Cholethiasis • COPD

16. Differentials • Aortic Dissection • Endocarditis • Esophagitis • Shock • Myocarditis • Pericarditis • Pulmonary embolism

17. Mechanisms of Myocardial damage The severity of an MI is dependent of three factors • The level of the occlusion in the coronary • The length of time of the occlusion • The presence or absence of collateral circulation

18. Cardiac Biomarkers • Cardiac biomarkers are protein molecules released into the blood stream from damaged heart muscle • Since ECG can be inconclusive , biomarkers are frequently used to evaluate for myocardial injury • These biomarkers have a characteristic rise and fall pattern

19. Troponin T and I • These isoforms are very specific for cardiac injury • Preferred markers for detecting myocardial cell injury • Rise 2-6 hours after injury Peak in 12-16 hours Stay elevated for 5-14 days

20. Creatinine Kinase ( CK-MB) • Creatinine Kinase is found in heart muscle (MB), skeletal muscle (MM), and brain (BB) • Increased in over 90% of myocardial infraction • However, it can be increased in muscle trauma, physical exertion, post-op, convulsions, and other conditions

21. Creatine Kinase (MB) • Time sequence after myocardial infarction Begins to rise 4-6 hours Peaks 24 hours returns to normal in 2 days • MB2 released from heart muscle and converted to MB1. • A level of MB2 > or = 1 and a ratio of MB2/MB1 > 1.5 indicates myocardial injury

22. Myoglobin • Damage to skeletal or cardiac muscle release myoglobin into circulation • Time sequence after infarction Rises fast 2hours Peaks at 6-8 hours Returns to normal in 20-36 hours • Have false positives with skeletal muscle injury and renal failure

23. Renal Failure and Renal Transplantation • Diagnostic accuracy of serum markers of cardiac injury are altered in patients with renal failure • Cardiac troponins decreased diagnostic sensitivity and specificity in patients receiving renal replacement therapy • Current data show levels of troponin I are unaltered while levels of troponin T may be elevated

24. CBC • CBC is indicated if anemia is suspected as precipitant • Leukocytosis may be observed within several hours after myocardial injury and returns to levels within the reference range within one week

25. Chemistry Profile • Potassium and magnesium levels should be monitored and corrected • Creatinine levels must be considered before using contrast dye for coronary angiography and percutanous revascularization

26. C-reactive Protein (CRP) • C- reactive protein is a marker of acute inflammation • Patients without evidence of myocardial necrosis but with elevated CRP are at increased risk of an event

27. Chest X-Ray • Chest radiography may provide clues to an alternative diagnosis ( aortic dissection or pneumothorax) • Chest radiography also reveals complications of myocardial infarction such as heart failure

28. Echocardiography • Use 2-dimentional and M mode echocardiography when evaluating overall ventricular function and wall motion abnormalities • Echocardiography can also identify complications of MI ( e.g. Valvular or pericardial effusion, VSD)

29. Electrocardiogram • A normal ECG does not exclude ACS • High probability include ST segment elevation in two contiguous leads or presence of q waves • Intermediate probability ST depression • T wave inversions are less specific

30. Localization of MI • ST elevation only • Inferior wall- II, III, aVF • Lateral wall_ I, aVL, V4-V6 • Anteroseptal- V1-V3 • Anterolateral- V1-V6 • Right ventricular- RV4, RV5 • Posterior- R/S ratio >1 in V1 and T wave inversion

31. Therapy The goals of therapy in AMI are the expedient restoration of normal coronary flow and the maximum salvage of functional myocardium

32. Antiplatelet Agents • Aspirin at least 160mg immediately • Interferes with function of cyclooxygenase and inhibits the formation of thromboxane • ASA alone has one of the greatest impact on the reduction of MI mortality. • Clopidogrel, ticlopidine, have not been shown in any large scale trail to be superior to Aspirin in acute MI

33. Supplemental Oxygen • Because MI impairs the circulatory function of the heart, oxygen extraction by the heart and other tissues may be diminished • Supplemental oxygen should be administered to patient with symptoms and or signs of pulmonary edema or pulse oximetry readings less than 90%.

34. Nitrates • IV nitrates to all patients with MI and congestive heart failure, persistent ischemia, hypertension, or large anterior wall MI • Primary benefit vasodilator effect • Metabolized to nitric oxide in the vascular endothelium, relaxes endothelium • Vasodilatation reduces myocardial oxygen demand and preload and afterload

35. Beta-blockers • Recommended within 12 hours of MI symptoms and continued indefinitely • Reduces Myocardial mortality by decreasing arrythmogenic death • Decrease the rate and force of myocardial contraction and decreases overall oxygen demand

36. Unfractionated heparin • Forms a chemical complex with antithrombin III inactivates both free thrombin and factor Xa • Recommended in patients with MI who undergo PTCA or fibrinolytic therapy with alteplase

37. Low-molecular weight heparin • Direct activity against factors Xa and IIa • Proven to be effective in treating ACS that are characterized by unstable angina or non ST- elevation MI • Their fixed doses are easy to administer and laboratory testing to measure their therapeutic effect is not necessary makes them attractive alternative of un-fractionated heparin

38. Thrombolytics • Indicated with MI and ST segment elevation greater than 0.1mV in 2 contiguous ECG leads, or new onset LBBB, who present less than 12 hours but not more than 24 hours after symptom onset • The most critical variable in achieving successful fibrinolysis is time form symptom onset to drug administration

39. Thrombolytics • As a class the plasminogen activators have been shown to restore coronary blood flow in 50-80% of patients • Contraindication active intracranial bleeding, CVA 2months, CNS neoplasm, HTN, coagulopathy • Retaplase slightly higher angiographic patency but did not translate into survival benefit • Intracranial bleed risk major drawback

40. Percutanous Coronary Intervention • Alternative if performed by skilled operator in an experienced center • Standard is a “ door to balloon” time of 90 minutes • PCI can successfully restore coronary blood flow in 90 to 95% of MI patients • PCI definitive survival advantage over fibrinolytics for MI patients who are in cardiogenic shock

41. Surgical Revascularization • Emergent or surgical revascularization in setting of failed PTCA in patients with hemodynamic instability and coronary anatomy amendable to surgical grafting • Also indicated of mechanical complications of MI including VSD, free wall rupture, or acute MR • Carries a higher risk of perioperative mortality than elective CABG

42. Lipid Management • All post MI patients should be on AMA step II diet ( < 7% of calories from saturated fats) • Post MI patients with LDL > 100 mg/dl are recommended to be on drug therapy to try to lower levels to <100 mg/dl • Recent data indicate that all MI patients should be on statin therapy, regardless of lipid levels or diet

43. Long term Medications • Most oral medications instituted in the hospital at the time of MI are continued long term • Aspirin, beta blockers and statin are continued indefinitely • ACEI indefinitely in patients with CHF, ejection fraction <.40, hypertension, or diabetes

44. Thank You!