Electrocardiogram Basics

Electrocardiogram (ECG)

• ECG is the recording of the electrical activity of the heart on a graph paper.
• Alternatively, it's a graphical representation of the heart's electrical activity.
• ECG is an acronym for ElectroCardioGraphy.
• The word originates from:
  • Electro (Greek for electricity)
  • Cardio (Greek for heart)
  • Graph (Greek root meaning "to write")

Heart Conduction System

• The heart's electrical activity is depicted by the ECG.
• Components of the system include:
  • SA Node
  • Interatrial Pathways
  • AV Node
  • Bundle of His
  • Bundle Branches
  • Purkinje Fibers

Significance of ECG

• ECG provides information about the heart rate and rhythm.
• It aids in diagnosing various heart conditions like:
  • Hypertrophy
  • Ischemia
  • Infarction
  • Arrhythmias
  • Conduction problems
  • Pacemaker activity
• However, ECG does not assess mechanical activity of the heart.

ECG Paper

• ECG paper is a long strip of paper with small squares.
• Each square measures 1mm by 1mm.
• Thick lines, called major divisions separate smaller squares.
• Five small squares sit between major divisions on ECG paper.
• The speed of the ECG machine is 25mm per second.
• The time duration of one small square on the ECG paper is 0.04 seconds.

ECG Paper Dimensions

• One millimetre (mm) horizontally represents 0.04 seconds.
• One millimetre (mm) vertically represents 0.1 millivolts (mV).
• Horizontally, 5mm = 0.20 seconds.

ECG Waves and Intervals

• The electrical activity is characterized by five primary wave deflections (P, Q, R, S, and T), which represent different stages of the heart's cycle.
• Various segments (e.g., PR, ST) and intervals (e.g., PR, QT) between these waves also provide diagnostic detail.

ECG Leads

• Leads are electrodes that record the electrical potential of the heart at different sites.
• There are 12 ECG leads:
  • 3 Bipolar Limb Leads (e.g., I, II, III)
  • 3 Augmented Limb Leads (e.g., aVR, aVL, aVF)
  • 6 Chest Leads (V1 to V6)

Anatomical Groups of Leads

• Leads are categorized by their anatomical location on the heart these group leads into:
  • Inferior leads
  • Septal leads
  • Anterior leads
  • Lateral leads

Examples of ECG Rhythms

• Normal Sinus Rhythm, Ventricular Tachycardia, Ventricular Fibrillation, ST Elevation and ST Depression