Lecture Notes: 12-Lead EKG Interpretation

Introduction to 12-Lead EKG Interpretation

• Basics of EKG interpretation.
• Importance of understanding coronary artery anatomy.
• Main coronary arteries: Left Main Coronary Artery and Right Main Coronary Artery.
  • Supply myocardium with oxygenated blood.
  • Branches supply different areas of the myocardium.

Coronary Artery Anatomy

• Left Main Coronary Artery
  • Supplies left ventricle, interventricular septum, part of right ventricle, and heart's conduction system.
  • Major branches:
    • Left Anterior Descending (LAD)
    • Circumflex
• Right Coronary Artery
  • Supplies right atrium, right ventricle, posterior/inferior right ventricle, part of conduction system.
  • Major branches:
    • Posterior Descending Artery
    • Marginal Branch

Importance of Coronary Anatomy in EKG Interpretation

• Understanding coronary anatomy is crucial for interpreting 12-lead EKGs.
• Test questions often involve identifying affected coronary artery based on EKG.

Lead Placement

• Limb leads must be placed on limbs for accurate view of myocardium.
• Chest Lead Placement (Precordial Leads):
  • V1: 4th intercostal space, right of sternum.
  • V2: 4th intercostal space, left of sternum.
  • V4: 5th intercostal space, left mid-clavicular line.
  • V3: Between V2 and V4.
  • V5: Left anterior axillary line.
  • V6: Mid axillary line.

EKG Evaluation

• Global Negativity:
  • Downward deflection in all leads can indicate limb lead misplacement.
• R Wave Progression:
  • Progression from negative (V1) to positive (V6).

Goals of 12-Lead ECG

• Recognize and localize acute myocardial infarction.
• Understand associated coronary artery anatomy.
• A normal 12-lead does not rule out acute myocardial infarction (consider non-STEMI).

EKG Interpretation

• Machine-printed data is diagnostic; interpretation should be cautious.
• Do not rely solely on machine interpretation for diagnosis.

ST Segment Elevation

• Finding J Point:
  • End of QRS, beginning of ST segment.
  • Compare ST segment height to preceding TP segment.
• Criteria for STEMI:

  • 1mm elevation in 2 or more contiguous leads.

Pathological Q Waves

• Indicate previous infarction if >0.04 seconds.
• Sub-endocardial vs. Transmural MI.

Anatomically Contiguous Leads

• Awareness of lead groupings essential for identifying MI location.
• Lead groupings:
  • Lateral: I, AVL, V5, V6
  • Inferior: II, III, AVF
  • Septal: V1, V2
  • Anterior: V3, V4

Reciprocal Changes

• Inferior vs. Lateral leads often show reciprocal changes.
• Example: Elevation in inferior leads may show depression in lateral leads.

Specific MI Patterns

• Extensive Anterior Wall MI (Widowmaker):
  • Elevation in septal, anterior, lateral leads.
  • Indicates high occlusion in left main coronary artery.
• Inferior Wall MI:
  • Often involves right coronary artery.
  • Check for right ventricular infarction using right-sided EKG.

EKG Imitators

• Bundle Branch Blocks (BBB):
  • Right BBB: Can still interpret EKG.
  • Left BBB: True imitator, cannot interpret for STEMI.
• Ventricular Rhythms:
  • Mask or mimic STEMI.
• Left Ventricular Hypertrophy (LVH):
  • Identify using specific criteria (negative deflection in V1/V2 and positive in V5/V6).

Other Considerations

• Digitalis Effect:
  • Sagging ST segment due to repolarization issues.
• Delta Wave:
  • Indicative of Wolf-Parkinson-White syndrome.
• Osborne Wave (J Wave):
  • Associated with hypothermia.

Conclusion

• Regular practice with EKGs is crucial.
• Misinterpretation can occur; rely on systematic approach.
• Recognize EKG imitators.
• Know when a right-sided EKG is necessary for inferior wall MI.

Note: Practice interpreting EKGs systematically to build confidence and accuracy.