Myocardial Infarction (MI)

Myocardial Infarction (MI)

David Ray Velez, MD

Table of Contents

Definitions
Diagnosis
Treatment
Complications

Definitions

Basics

  • Coronary Artery Disease is the Most Common Cause of Death in the United States
  • 95% of Myocardial Ischemia is Due to Underlying Atherosclerotic CAD
  • Most Atherosclerosis is Proximal
  • Risk Factors for Increased Mortality:
    • Cardiogenic Shock – Strongest Risk Factor
    • Emergency Setting
    • Increased Age
    • Low Ejection Fraction

Definitions

  • Acute Coronary Syndrome (ACS): A Constellation of Clinical Symptoms Consistent with Acute Myocardial Ischemia
    • Includes Myocardial Infarction (MI) and Unstable Angina (UA)
  • Coronary Artery Disease (CAD): Diseased/Damaged Coronary Blood Vessels
  • Angina Pectoris: Severe Chest Pain Due to Inadequate Cardiac Blood Supply
  • Myocardial Infarction (MI/Heart Attack): Death of Myocardial Cells Due to Obstruction of Blood Flow

Types of Angina Pectoris

  • Stable Angina: Brief Episodes Associated with Exercise or Stress and Relieved with Rest
  • Unstable Angina (UA)
    • Prolonged Angina at Rest (> 20 Minutes)
    • New-Onset Severe Angina
    • Worsening Angina (More Frequent, Severe, or Longer Duration)
  • Variant/Prinzmetal Angina: Angina Due to Coronary Artery Spasm

Types of Myocardial Infarction (MI)

  • ST-Segment Elevation Myocardial Infarction (STEMI): MI Associated with an ST-Segment Elevation
    • Indicates a Full-Thickness Injury
  • Non-ST-Segment Elevation Myocardial Infarction (NSTEMI): MI Not Associated with an ST-Segment Elevation
    • Indicates a Subendocardial (Not Full-Thickness) Injury
    • Type 1 NSTEMI – Spontaneous from Atherothrombotic Plaque Rupture or Erosion
    • Type 2 NSTEMI – Due to Oxygen Supply-Demand Imbalance
    • Type 3 NSTEMI – Cardiac Death without Biomarker Samples or Detected at Autopsy
    • Type 4 NSTEMI – Associated with Revascularization Procedures
      • 4a: Related to Percutaneous Coronary Intervention (PCI) within 48 Hours
      • 4b: Related to Stent Thrombosis
      • 4c: Restenosis After Percutaneous Coronary Intervention (PCI)
    • Type 5 NSTEMI – Related to CABG Procedure within 48 Hours

STEMI on EKG

Diagnosis

Presentation

  • Chest Pain/Discomfort – Most Common Symptom
    • Classic Description: Substernal Chest Tightness/Pressure with Radiation to Left Arm or Jaw
    • “Feels like an Elephant Standing on My Chest”
  • Shortness of Breath
  • Diaphoresis
  • Weakness
  • Anxiety

Diagnosis of Myocardial Infarction (MI)

  • Elevated Troponin with ≥ One Of:
    • Symptoms of Myocardial Ischemia
    • New Ischemic Changes on EKG
    • Development of Pathologic Q Waves
    • New Loss of Viable Myocardium or Regional Wall Motion Abnormality Consistent with Ischemic Etiology on Imaging
    • Identification of a Coronary Thrombus by Angiography or Autopsy
  • Coronary Angiogram is the Standard Tool for Describing Surgical Anatomy of CAD

Differentiation

  • STEMI: Elevated Troponin with ST-Elevation on EKG
  • NSTEMI: Elevated Troponin without ST-Elevation on EKG
  • UA: Normal Troponin

EKG Changes

  • ST-Segment Changes (Elevation or Depression)
  • Left Bundle Branch Block (LBBB)
  • T Wave Inversion
  • Q Waves
  • Lead Laterality:
    • Anterior: V1-V4 (Indicates Left Anterior Descending (LAD) Artery Disease)
    • Posterior: V1 and V2 (Indicates Right Coronary Artery or Left Circumflex Artery Disease)
    • Lateral: I and aVL (Indicates Left Circumflex Artery Disease)
    • Inferior: II, III, and aVF (Indicates Right Coronary Artery Disease)

Cardiac Enzymes

  • Troponin I
    • Best Test for Detecting Acute MI
    • Highest Sensitivity and Specificity
    • Remains Elevated for 5-14 Days
    • Generally Trended Every 3-6 Hours
  • Creatine Kinase-MB (CK-MB)
    • Remains Elevated for 2-3 Days
    • Best for Detecting Recurrence

Treatment

Cardiogenic Shock

Medical Managements

  • Oxygen Supplementation
  • Antiplatelet Therapy (Aspirin or Clopidogrel (Plavix))
    • Other NSAIDs Should Be Discontinued – Increased Risk of Cardiovascular Events
  • Beta Blockers
    • Contraindicated in Heart Failure, Heart Block, or Cardiogenic Shock
  • HMG-CoA Reductase Inhibitor (Statin)
  • Sublingual Nitroglycerin – Vasodilation to Relieve Chest Pain
    • Contraindicated in Hypotension or Cardiogenic Shock
  • Consider Morphine for Persistent Severe Pain

Reperfusion

  • STEMI Requires Early Reperfusion – The Most Important Factor in Improving Survival
  • Options:
    • Percutaneous Coronary Intervention (PCI)
      • Preferred Approach if a Cath Lab is Immediately Available
      • Goal Door-to-Balloon Time < 90 Minutes
    • Fibrinolysis
    • Coronary Artery Bypass Graft (CABG)

Percutaneous Coronary Intervention (PCI)

  • PCI Generally Refers to Coronary Angioplasty with Stent Placement
  • Radial Access is Generally Preferred Over Femoral Access (Decreased Risk of Bleeding Complications)
  • Stent Types:
    • Drug-Eluting Stents (DES)
      • Polymer Coating with Compounds Used to Decrease the Risk of Restenosis
      • Generally Preferred but Require Longer Anticoagulation
    • Bare Metal Stent (BMS)
  • Dual Antiplatelet Therapy (DAPT)
    • Most Common Agents: Aspirin and Clopidogrel (Plavix)
    • Duration of Therapy:
      • Drug-Eluting Stents (DES): One Year
      • Bare Metal Stent (BMS): One Month

PCI: Before (Left) and After (Right) 1

Coronary Artery Bypass Graft (CABG) Indications

  • Left Main Disease > 50% Stenosis
  • Triple-Vessel Disease > 70% Stenosis (RCA, LAD, and Circumflex)
  • Double-Vessel Disease Including the Proximal LAD
  • At Least One Vessel with Significant (> 70%) Stenosis and Unacceptable Angina Despite Medical Therapy
  • Survivors of Sudden Cardiac Death with Ischemia-Mediated Ventricular Tachycardia
  • Undergoing Noncoronary Cardiac Surgery with Left Main Disease (> 50%) or Any Other CAD (> 70%)
  • Emergency CABG:
    • After Failed Percutaneous Coronary Intervention (PCI) with Ongoing Ischemia or Threatened Occlusion of Substantial Myocardium
    • Cardiogenic Shock Due to Myocardial Infarction (MI)

Complications

Mechanical Complications After Acute MI

  • 3 Classic Presentations:
    • Papillary Muscle Rupture– Causes Severe Mitral Regurgitation with Fulminant Heart Failure and Pulmonary Edema
      • Posteromedial Papillary Muscle Rupture is Most Common Due to Singular Blood Supply (RCA/Inferior MI)
    • Interventricular Septum Rupture– Causes a Left-to-Right Shunt with Pulmonary Vascular Congestion
    • Left Ventricular Free Wall Rupture– Causes a Pericardial Effusion and Tamponade
  • Generally Present Around 3-5 Days After an MI
  • High Level of Concern for Patients that Become Acutely Hypotensive After an MI (High Mortality)
  • Temporization:
    • Afterload Reduction (Diuresis or Vasodilators) for Papillary Muscle or IV Septum Rupture
    • Fluids to Increase Preload for LV Wall Rupture
  • Usually Require Emergent Surgical Repair

Post-Cardiac Injury Syndrome (PCIS)

  • Also Known As:
    • Dressler’s Syndrome
    • Post-Pericardiotomy Syndrome
    • Post-Myocardial Infarction Syndrome
  • Definition: Pericarditis from Injury to the Pericardium
  • Develops Weeks-Months After Myocardial Infarction (MI)
  • Presentation:
    • Pericardial Friction Rub
    • Fever
    • Pleuritic Chest Pain
    • Shortness of Breath
    • Can Cause Pericardial Effusion
  • EKG Findings: Diffuse ST-Segment Elevation
  • Treatment: NSAIDs, Colchicine, and Steroids

Other Complications

  • Reinfarction
    • Generally Occurs Within 48 Hours
  • Postinfarct Angina
  • Conduction Abnormalities
  • Left Ventricular Aneurysm

References

  1. JHeuser. Wikimedia Commons. (License: CC BY-SA-3.0)