Basics of EKGs Lecture

Introduction

• Understanding the basics of EKGs is essential before reading 12-lead EKG cases.
• Importance of grasping the physics and physiology involved.

Physics and Physiology of EKGs

• Ventricular Myocardium & Electrodes

  • Positive and negative electrodes are placed on the tissue.
  • Electrical stimulus causes depolarization (influx of positive ions, e.g., calcium, sodium).
  • Depolarization propagates through gap junctions from cell to cell.

• Deflections on EKG

  • Positive Deflection: Positive charges moving towards a positive electrode.
  • Negative Deflection: Positive charges moving away from a positive electrode.
  • Isoelectric Line: No net movement or perpendicular electrical activity to the lead.

Understanding the EKG Waveform

• Lead II Analysis
  • P Wave: Represents atrial depolarization.
  • PR Segment: No net movement, corresponds to electrical activity being held in the AV node.
  • Q Wave: Represents septal depolarization.
  • R Wave: Represents ventricular depolarization, particularly large for the left ventricle.
  • S Wave: Basal ventricular depolarization.
  • T Wave: Ventricular repolarization, occurs due to negative charge moving towards a negative electrode.

12-Lead EKG System

• Limb Leads: Lead I, II, III

  • Lead I: High lateral wall of the left ventricle.
  • Lead II, III: Inferior wall of the heart.

• Augmented Limb Leads (aVR, aVL, aVF):

  • aVR: Right ventricle and basal septum.
  • aVL: High lateral wall of the left ventricle.
  • aVF: Inferior wall of the heart.

• Precordial Leads (V1-V6):

  • V1, V2: Right ventricle.
  • V2, V3: Basal septum.
  • V2-V4: Anterior wall of the heart.
  • V5, V6: Lateral wall of the left ventricle.

• R to S Progression: From V1 to V6, R wave should increase and S wave should decrease.

Components of EKG Strip

• Large Box:

  • Width: 5 mm = 0.20 seconds
  • Height: 5 mm = 0.5 millivolts

• Small Box:

  • Width: 1 mm = 0.04 seconds
  • Height: 1 mm = 0.1 millivolts

• Important Intervals:

  • PR Interval: <0.20 seconds (less than one large box)
  • QRS Complex: <0.12 seconds (less than three small boxes)
  • QT Interval: Varies by gender, generally <430 ms for males, <460 ms for females

Conclusion

• Understanding the waveform, lead placement, and what each wave represents is crucial for interpreting EKGs effectively.
• EKGs provide insight into the electrical activity and health of the heart. Further analysis requires understanding of pathologies associated with segment and interval abnormalities.