Electrocardiogram (ECG/EKG) Overview

Introduction

• ECG/EKG: A tool to visualize heart's electrical activity.
• Function: Shows how depolarization wave during each heartbeat appears based on electrode setup.

Basic Concepts

• Depolarization Wave: A wave of positive charge moving through the heart.
• Electrodes Setup: Example of Lead II with electrodes on the right arm and left leg.
  • Positive deflection when wave moves toward the left leg electrode.

Electrical Activity & Dipoles

• Cell Charge at Rest: Negatively charged relative to the outside.
• Depolarization: Cells become positively charged, creating a dipole (difference in charge).
• Dipole Vector: Points toward the positive charge, detected by electrodes.
  • Positive deflection on ECG corresponds to dipole direction toward positive electrode.
  • No dipole results in no deflection.
  • Repolarization wave causes negative deflection when vector points to negative electrode.

ECG Tracing

• Vector Components: Parallel component causes deflection.
  • Perpendicular component causes no deflection.
  • Magnitude of deflection relates to dipole size in electrode direction.

Standard ECG Setup

• 10 Electrodes Total:
  • 4 limb electrodes (left arm, right arm, left leg, right leg - neutral).
  • 6 precordial electrodes (V1-V6 on the chest).
• Planes of Heart:
  • Transverse Plane: V1-V6 detect waves in the chest area.
  • Coronal Plane: Augmented vector right (aVR), left (aVL), and foot (aVF) detect waves vertically.

Limb and Chest Leads

• Bipolar Limb Leads: Lead I, II, III using two electrodes each.
  • Lead I: Right arm (-) to left arm (+).
  • Lead II: Right arm (-) to left leg (+).
  • Lead III: Left arm (-) to left leg (+).
• 12-Lead ECG: 6 limb leads and 6 chest leads.

Viewing Heart's Activity

• Purpose: Different leads provide different views to trace depolarization.
• Example: QRS complex appearance varies across chest leads (V1-V6).
• Lead Categories:
  • Inferior Leads: II, III, aVF (inferior heart wall).
  • Lateral Leads: I, aVL, V5, V6 (lateral heart wall).
  • Septal Leads: V1, V2 (interventricular septum).
  • Anterior Leads: V3, V4 (anterior heart wall).

Importance

• Diagnosis: Specific lead issues might indicate heart region diseases.
• Summary: 12-lead ECG offers comprehensive insights into heart function and structure.