Electrocardiogram in Myocardial Infarction

Aka: Electrocardiogram in Myocardial Infarction, EKG in Acute MI, EKG in Myocardial Ischemia, EKG in Cardiac Ischemia, EKG Markers of Underlying Coronary Artery Disease

1. See Also
   1. ST Elevation causes
2. Advantages
   1. Ischemic EKG changes best acute MI evidence
      1. Applies if symptom onset within last 3 hours
   2. Normal/Nondiagnostic initial EKG predicts low risk
3. Disadvantages
   1. Poor sensitivity for Myocardial Infarction (40-50%)
      1. 3-10% of MI patients have initial normal EKG
      2. 25% of patients with missed MI had misread EKG
4. Precautions
   1. The computer over-reads abnormal EKGs
   2. Compare with prior EKGs (Increases Specificity)!
5. Images
   1. Acute ST Elevation Myocardial Infarction with delayed presentation (ST Elevation and Q waves present)
      1. 
6. Findings: EKG Markers of underlying CAD
   1. Left Ventricular Hypertrophy
   2. ST segment changes
   3. T Wave changes
   4. Diagnostic Q Waves in 2 contiguous leads
   5. Left Bundle Branch Block or other conduction changes
7. Findings: General EKG Changes suggestive of Ischemia
   1. Electrocardiogram may be completely normal
   2. ST Elevation or ST depression
      1. Over 1 mm ST changes that are transient with symptoms
      2. Summed ST deviation (sum of affected leads) >2.5 mm
         1. Holmvang (2003) J Am Coll Cardiol 41:905-15
   3. Deep symmetric T-wave inversion
      1. Occurs in multiple precordial leads
   4. Left main Coronary Artery stenosis marker
      1. aVR ST segment elevation > V1 ST segment elevation
      2. Gaitonde (2003) Am J Cardiol 92:846-8
8. Findings: General EKG Changes suggestive of acute MI
   1. New left ventricular strain pattern
   2. New Left Bundle Branch Block
   3. Q Waves (.04 sec and 1/3 height of R Wave)
      1. Unless isolated in Lead III
   4. T Wave inversion
      1. Unless isolated to Lead III or Lead V1
   5. ST-T elevation (>1mm in limb or precordial leads)
      1. Must have >=2 concordant leads with changes
   6. ST depression in Lead V1, Lead V2 (Posterior MI)
   7. Hyperacute T Waves (over 50% of preceding R)
      1. Must have 2 or more leads with changes
9. Findings: Septal MI Anatomic Distribution
   1. Electrocardiogram Changes
      1. Lead V1 to lead V2
   2. Distribution
      1. Left Coronary Artery: LAD-Septal Branch
   3. Complications
      1. Infranodal and Bundle Branch Block
10. Findings: Anterior MI Anatomic Distribution
    1. EKG Changes
       1. Lead V3 to lead V4
    2. Distribution
       1. Left Coronary Artery: LAD-Diagonal branch
    3. Complications
       1. Bad prognosis
       2. High risk of sudden death
       3. High risk of Congestive Heart Failure in first year
       4. Complete Heart Block
11. Findings: Inferior MI Anatomic Distribution
    1. EKG Changes
       1. Lead II, Lead III, and Lead aVF
    2. Distribution
       1. Right Coronary Artery: Posterior descending branch
    3. Complications
       1. Distended neck veins with clear lungs
       2. Systolic Blood Pressure drops with
          1. Morphine
          2. Nitroglycerin
       3. Right Ventricular Infarction
12. Findings: Lateral MI Anatomic Distribution
    1. EKG Changes
       1. ST segment elevation in leads V5, V6, I, AVL
       2. ST segment depression in leads V1, V2, V3
    2. Distribution
       1. Left Coronary Artery: Circumflex branch
    3. Complications
       1. Left Ventricular Dysfunction
       2. AV nodal block
13. Findings: RV Infarction Anatomic Distribution
    1. EKG Changes
       1. Lead V4R (Lead V4 placed on Right chest)
    2. Distribution
       1. Right Coronary Artery: Proximal branches
    3. Complications
       1. Diagnosis >1mm ST Elevation in V4R
       2. Suspect in Inferior MI
14. Findings: Posterior Infarction Anatomic Distribution
    1. EKG Changes
       1. Lead V1 to Lead V4 ST depression
    2. Distribution
       1. Left Coronary Artery: Circumflex
       2. Right Coronary Artery: Posterior descending
    3. Complications
       1. Left Ventricular Dysfunction