Lecture Notes: Understanding Pathologic Q Wave

Introduction

• Topic: Pathologic Q Wave in electrocardiography (EKG/ECG)
• Importance: Distinguishing normal Q waves from pathologic ones seen during myocardial infarction (MI)

Normal Q Wave

• QRS Complex: Comprises Q, R, and S waves
  • Q Wave: First negative deflection in the QRS complex
  • R Wave: Positive deflection
  • S Wave: Negative deflection
• Not Always Visible: Often, Q wave is not visible and that's considered normal.
• No Positive Deflection Before Q: If any positive deflection exists before the Q, it is not considered a Q wave.

QS Wave

• Confusion in Identification: Some waves can be hard to classify as Q or S wave.
• Definition: A wave with two negative deflections (Q and S) is termed a QS wave.

Pathologic Q Wave

• Characteristics:
  • Large size compared to normal Q waves
  • Often accompanied by ST segment elevation
• Indicative of MI: Suggests myocardial infarction; not seen immediately in acute MI but several hours to days post-MI.
• Persistence: May indicate old MI, showing scar tissue and absence of electrical activity.

EKG Interpretation

• Acute MI:
  • Initial sign: ST segment elevation
  • Q wave appears: 6-8 hours later, persisting as proof of earlier MI
• Reperfusion Impact: Early reperfusion can prevent permanent Q wave formation.

Practical Examples

• Identifying Pathologic Q Waves:
  • Look for large Q waves following P wave but preceding R wave
  • Associated with ST segment elevation
• Old vs. Recent MI:
  • Old MI: Q wave without ST segment elevation
  • Recent MI: Q wave with ST segment elevation

EKG Examples and Analysis

• Lead Observations:
  • Q waves are prominent in leads II, III, and aVF
  • Presence and size of Q wave in relation to R wave are key indicators
  • ST segment elevation confirms recent MI
• Diagrammatic vs. Real EKG: Easier to interpret diagrams due to clarity.

Conclusion

• Recognition Skills: Understanding how to differentiate between normal and pathologic Q waves is crucial.
• Future Learning: Subsequent discussions will cover identifying infarct location in the heart based on EKG leads.

Note: These notes summarize key aspects of distinguishing normal and pathologic Q waves in EKGs, which is vital for diagnosing myocardial infarction accurately.