Electrocardiogram (ECG or EKG)

Overview

• ECG/EKG: A tool to visualize electricity through the heart.
• Depolarization wave: Wave of positive charge during each heartbeat.
• Appearance depends on the electrode set used (e.g., lead II).

Basic Concepts of ECG

• Electrodes: Example of lead II with electrodes on the right arm and left leg.
  • Positive deflection when wave moves toward left leg electrode.
• Cell Charge:
  • At rest: cells are negatively charged compared to the outside.
  • Depolarization: cells become positively charged.
• Dipole: Difference in charge across cells during depolarization.
  • Represented as a vector pointing towards the positive charge.
  • ECG tracing shows a positive deflection if dipole points towards positive electrode.
  • No dipole or deflection when cells are fully depolarized.

ECG Tracing

• Depolarization Patterns:
  • Wave moving at an angle causes smaller deflection due to perpendicular vector component.
  • No deflection if wave is perpendicular to electrodes.

Electrode and Lead Details

• Electrodes: 10 total (4 limb, 6 precordial chest electrodes).
  • Limb electrodes: Left arm, right arm, left leg, right leg (neutral).
  • Precordial electrodes: V1 through V6 wrap around the chest in a transverse plane.
• Leads:
  • Non-neutral leads: aVR, aVL, aVF.
    • aVR: Right arm, vector 30 degrees up from horizontal.
    • aVL: Left arm, vector 30 degrees up from horizontal.
    • aVF: Left foot, vector facing down.
  • Bipolar limb leads: Lead 1, 2, 3.
    • Lead 1: Right arm (-), Left arm (+).
    • Lead 2: Right arm (-), Left leg (+).
    • Lead 3: Left arm (-), Left leg (+).
  • Total: 6 limb leads + 6 chest leads = 12-lead ECG.

Importance of Multiple Leads

• Provides different views of the heart.
• QRS Complex: Varying depolarization wave appearances in different leads.

Lead Grouping and Heart Regions

• Inferior Leads: Leads II, III, aVF near inferior heart wall (right coronary artery).
• Lateral Leads: Leads I, aVL, V5, V6 near lateral wall (left circumflex artery).
• Septal Leads: V1, V2 near interventricular septum.
• Anterior Leads: V3, V4 near anterior wall (left anterior descending artery).

Recap

• 10 electrodes create 12 leads to show positive charge movement.
• Lead views help assess heart structure and function.