Acute Myocardial Infarction

1. Acute Myocardial Infarction Willis E. Godin D.O., FACC

2. Acute Myocardial Infarction • Definition: • Decreased delivery of oxygen and nutrients to the myocardium • Myocardial tissue necrosis causing irreparable tissue/cell death

3. Pathophysiology • The most frequent cause of an acute MI is a disruption in the vascular endothelium that is associated with myocardial plaque • Plaque occurs over a period of years to decades • This combination causes the development of an intra-coronary thrombus, which causes the coronary artery to occlude • Within 20-40 minutes of an occlusion, irreversible myocardial cell damage/death occurs

4. Pathophysiology • 2 primary characteristics of plaque development are 1) a fibromuscular cap and 2) an underlying lipid rich core. • The overall loss of structural stability of the plaque usually occurs at the junction between the fibromuscular cap and the vessel wall (shoulder region) • Thrombus develops (due to the platelet-mediated activation of the coagulation cascade) and partial or complete occlusion occurs causing an acute myocardial infarction.

7. Pathophysiology • The severity of an MI depends on three factors • 1) The level of the occlusion in the coronary artery • Generally, the more proximal the coronary occlusion, the more extensive the amount of myocardium that will be at risk of necrosis • 2) The length of time of the occlusion • The longer the period of vessel occlusion, the greater the chances of irreversible myocardial damage distal to the occlusion • 3) The presence or absence of collateral circulation

8. Pathophysiology • STEMI • “complete” blockage of a coronary artery • NSTEMI • “near-complete” blockage of a coronary artery

9. Pathophysiology • Left Coronary Artery • Left Anterior Descending Artery (LAD) • “widow maker” • Anterior MI • Lateral MI • Left Circumflex Artery (LCx) • Lateral MI • Posterior MI • Right Coronary Artery • Inferior MI • RV MI

11. Prevalence • Myocardial Infarction is the leading cause of death in the United States • Approximately 450,000 people in the US die from coronary disease per year • 50% of all acute MI’s in the US occur in people under the age of 65 • No longer considered a “disease of the elderly”

12. Risk Factors • Dyslipidemia • Diabetes Mellitus • Hypertension • Tobacco use • Family History • Male gender

13. Diagnosis • Symptoms (gained by an accurate history) • Electrocardiogram (ECG) • Laboratory Tests • CK • CK-MB • Troponin • Echocardiogram

14. Symptoms • Chest pain described as a pressure sensation, fullness, or squeezing in the midportion of the thorax • Radiation of chest pain into the jaw or teeth, shoulder, arm, and/or back • Associated dyspnea or shortness of breath • Associated epigastric discomfort with or without nausea and vomiting • Associated diaphoresis or sweating • Syncope or near syncope without other cause • Impairment of cognitive function without other cause

16. Electrocardiogram • ST elevation myocardial infarction (STEMI) • > 1mm ST elevations in contiguous leads • Non-ST elevation myocardial infarction (NSTEMI) • ST depression • T wave inversions • No obvious ECG changes

17. ECG - STEMI

18. ECG - STEMI

19. ECG -NSTEMI

20. ECG - NSTEMI

21. ECG - NSTEMI

22. Cardiac Enzymes • Serial blood draws • Every 4 hours x 4 sets • Myoglobin peaks first (detectable in 1-4 hrs) • Troponin • peaks last (detectable in 3-12 hrs) • most specific • remains detectable in serum the longest

23. Cardiac Enzymes

24. Cardiac Enzymes

25. Imaging (Echocardiography) • An echocardiogram can be performed to assess areas of the left ventricle that are not contracting normally as compared to areas that are contracting normally • After normal blood flow is interrupted, the area of the myocardium affected by the occluded artery will not function normally. • This abnormal wall motion can be detected by echocardiography

26. Treatment • Antiplatelets • Supplemental oxygen • Nitrates • Pain control • Beta Blockers • Statin Therapy • Heparin (unfractionated / low-molecular-weight heparin) • Fibrinolytics • Angiotensin-Converting Enyme Inhibitors / Angiotensin Receptor Blockers • Glycoprotein Iib/IIIa Antagonists • Aldosterone Antagonists

27. Other Treatment Options • Percutaneous Coronary Intervention • PCI / coronary stenting • Surgical Revascularization • CABG • Implantable Cardiac Defibrillators • AICD

33. Treatment Outcomes • Long-term medications • Smoking cessation • Cardiac Rehabilitation

34. Long-Term Medications • Most oral medications instituted in the hospital at the time of acute MI will be continued long term • Aspirin, beta blockade, and statin therapy is continued indefinitely in all patients • ACE inhibitors are continued indefinitely in patients with CHF, left ventricular dysfunction, hypertension, or diabetes • Diet modification, regular exercise

35. Smoking Cessation • Smoking is a major risk factor for coronary artery disease and MI • For patients who have undergone an MI, smoking cessation is essential to recovery, long-term health, and prevention of re-infarction • In one study, the risk of recurrent MI decreased by 50% after 1 year of smoking cessation

36. Smoking Cessation • All STEMI and NSTEMI patients with a history of smoking should be advised to quit and offered smoking cessation resources • Nicotine replacement therapy • Pharmacologic therapy • Referral to behavioral counseling or support groups • Smoking cessation counseling should begin in the hospital, at discharge, and during follow up

38. Cardiac Rehabilitation • Provides a venue for continued education, reinforcement of lifestyle modification, and adherence to a comprehensive prescription of therapies for recovery from MI including exercise training • Participation in cardiac rehabilitation programs after MI is associated with decreases in subsequent cardiac morbidity and mortality • Other benefits include improvements in quality of life, functional capacity, and social support

39. Summary • MI results from myocardial ischemia and cell death, most often because of an intra-arterial thrombus superimposed on an ulcerated or unstable atherosclerotic plaque • Despite advances in therapy, MI remains the leading cause of death in the United States. • MI risk factors include hyperlipidemia, diabetes, hypertension, male gender, and tobacco use. • Diagnosis is based on the clinical history, ECG, and blood test results, especially creatinephosphokinase (CK), CK-MB fraction, and troponin I and T levels.

40. Summary • Outcome following an MI is determined by the infarct size and location, and by timely medical intervention. • Aspirin, nitrates, and beta blockers are critically important early in the course of MI for all patients. • Post-discharge management requires ongoing pharmacotherapy and lifestyle modification.