Lecture Notes: R-Wave Progression and Axis Determination

Introduction

• Overview of r-wave progression through precordial leads (V1-V6) and hexaxial leads (I, II, III, aVR, aVL, aVF).
• Discussion of QRS complex directions and the difference between a vector and an axis.
• How to determine a mean electrical axis and practice on axis deviation.
• Causes of different axis deviations.

Understanding Depolarization and EKG

• Depolarization in the heart is a 3D process; EKG provides a 2D interpretation.
• A 12-lead EKG provides multiple perspectives to reconstruct the 3D pathway.

Hexaxial Leads

• Hexaxial leads: I, aVL, II, III, aVF, aVR.
• These leads provide an up-down and left-right pathway for depolarization.
• Importance of aVR in providing a negative deflection in normal hexaxial r-wave progression.

R-Wave Progression

• Normal R-Wave Progression Through Hexaxial Leads:

  • Leads I, II, III, aVL, aVF should show positive QRS deflection.
  • aVR should show a negative QRS deflection.

• Abnormal R-Wave Progression:

  • Examples include lead I being primarily negative and aVL being negative.
  • Poor r-wave progression indicates abnormal depolarization patterns.

Precordial Leads

• Normal R-Wave Progression:

  • V1 and V2 should be primarily negative.
  • V3 and V4 should transition from negative to positive.
  • V5 and V6 should be primarily positive.

• Abnormal R-Wave Progression:

  • No transition from negative to positive, indicating poor r-wave progression.

Vectors and Axis Determination

• Vector vs Axis:

  • Vector: Direction and strength of an electrical impulse for a cardiac cell.
  • Axis: Average direction of all vectors, resulting in the mean electrical axis.

• Plotting the Axis:

  • Use lead I and aVF for axis determination.
  • Plotting involves counting deflections and marking positions on the hexaxial reference plane.
  • Normal axis lies between 0° to +90°.
  • Right Axis Deviation (RAD) between +91° to +180°.
  • Left Axis Deviation (LAD) from -1° to -90°.
  • Indeterminate Axis is outside the normal range.

Causes of Axis Deviations

• Left Axis Deviations (LAD):

  • Normal in older/obese people, high diaphragm.
  • Left ventricular hypertrophy, left anterior fascicular block.
  • Inferior wall MI, left bundle branch block.

• Right Axis Deviations (RAD):

  • Right ventricular hypertrophy, COPD.
  • Left posterior fascicular block, right bundle branch block.

Practice and Shortcut Methods

• Shortcut method for axis determination: "Right together, left apart."
• Understanding EKG plots and determining axis quickly.

Conclusion

• Multiple vectors in the heart help determine the mean electrical axis.
• Any deviation from the normal axis indicates possible abnormalities.
• Importance of understanding these patterns for diagnosing heart conditions.

Additional Resources

• Contact the instructor for further questions or clarification.