EKG Basics Lecture Notes

Introduction

• Overview of EKG basics focusing on physics and physiology.
• Aim to prepare for systematic approach to reading 12 lead EKG cases.

Physics and Physiology of EKGs

• Ventricular Myocardium: Cut a chunk and place electrodes (positive and negative).
• Electrical Stimulation:
  • Depolarization: Positive ions (calcium, sodium) flood into cells, creating a positive charge.
  • Gap Junctions: Allow movement of ions from cell to cell, propagating electrical signals.
  • Flow of Charges: Positive charges moving towards the positive electrode produce an upward deflection in the EKG.
  • Negative Deflection: Flow of positive charges away from the positive electrode produces a downward deflection.
  • Isoelectric Line: Flat line indicating no net movement or current perpendicular to the axis of the lead.

EKG Waveform Components

• Lead II: Most commonly used lead for rhythm strips.
• P Wave: Indicates atrial depolarization.
• PR Segment: Indicates the delay at the AV node.
• Q Wave: Indicates septal depolarization.
• R Wave: Indicates ventricular depolarization.
• S Wave: Indicates depolarization towards the bases of the ventricles.
• T Wave: Indicates ventricular repolarization.

Key Points to Remember

• Positive Charges: Flow towards positive electrode = upward deflection.
• Negative Charges: Flow towards negative electrode = upward deflection.
• Isoelectric Line: Indicates flat line when no net movement of electrical activity.

Understand the EKG Strips

• Lead II Axis: Negative electrode on the right arm, positive on the left leg.
• Mean Vector: Direction of positive charge flow determines deflections seen on EKG.
  • Atrial Depolarization: Downward and left towards the AV node = P Wave.
  • Delay at AV Node: Causes the flat PR Segment.
  • Ventricular Depolarization: R wave indicates the mean vector of depolarization towards left ventricle.
  • Repolarization: T wave indicates repolarization of ventricles.

EKG Measurement Basics

• Large Box: 5 mm width = 0.20 seconds.
• Small Box: 1 mm width = 0.04 seconds.
• Height of Boxes: Helps determine voltage (5 mm = 0.5 mV, 1 mm = 0.01 mV).

Intervals and Segments

• PR Interval: Normal <= 0.20 seconds.
• QRS Complex: Normal <= 0.12 seconds.
• QT Interval: Less than 430 ms in males, less than 460 ms in females. Prolonged QT can indicate risk of arrhythmias.

Conclusion

• Understanding EKG basics is crucial for analyzing heart activity.
• Utilize this foundational knowledge as we explore further into EKG interpretation.