EKG Basics Lecture Notes

Introduction

• Overview of EKGs: Importance of understanding physics and physiology
• Aim: Systematic approach to reading EKGs

Basic Concepts

• Ventricular Myocardium: Understanding electrical stimulation
• Electrodes: Positive electrode on one end, negative on the other

Electrical Activity in Myocardium

• Depolarization:
  • Positive ions (calcium, sodium) enter cells, causing depolarization (becoming positive)
  • Gap junctions allow movement of ions between cells
• Deflections on EKG:
  • Positive charge towards positive electrode: Upward deflection
  • Positive charge away from positive electrode: Downward deflection
  • Negative charge towards negative electrode: Upward deflection
  • Flat line: No net movement or perpendicular to lead axis

Lead II Overview

• Most commonly used lead in EKG strips
• Negative electrode on right arm, positive on left leg

Atrial Depolarization

• SA Node: Initiates depolarization in the right atrium
• Mean Vector Direction: Downward and left towards AV node
• P Wave: Indicates atrial depolarization (upward deflection)
• PR Segment: Reflects delay at AV node (flat line)
• PR Interval: From start of P wave to start of QRS

Ventricular Depolarization

• QRS Complex: Consists of Q, R, and S waves
  • Q Wave: Septal depolarization (downward deflection)
  • R Wave: Depolarization moving towards the left ventricle (upward deflection)
  • S Wave: Depolarization moving towards ventricles' base (downward deflection)
• ST Segment: Entire myocardium depolarized (flat line)
• T Wave: Ventricular repolarization (upward deflection)

EKG Waveform Summary

• P Wave: Atrial depolarization
• QRS Complex: Ventricular depolarization
• ST Segment: Ventricular depolarization complete
• T Wave: Ventricular repolarization

EKG Strip Components

Large Box and Small Box

• Large Box: 5 mm width & height, 0.20 seconds
• Small Box: 1 mm width & height, 0.04 seconds
• Voltage: 5 mm (0.5 mV) for large box, 1 mm (0.01 mV) for small box

Key Measurements

• PR Interval: Normal < 0.20 seconds
• QRS Duration: Normal < 0.12 seconds (3 small boxes)
• QT Interval:
  • Males < 430 ms
  • Females < 460 ms

Conclusion

• Need to understand various components of EKG and their clinical significance
• Importance of systematic analysis in interpreting EKG results

---