Electrocardiogram (ECG) / Electrocardiography

Electrocardiogram (ECG) / Electrocardiography

Basics Of ECG..

electrocardiograph

Introduction

  • Electrocardiogram records the graphical representation of electrical signals from the heart to rule out different heart conditions
  • Electrocardiography is a technique by which electrical activities of the heart is studied
  • Electrocardiograph (ECG Machine) is the instrument by which electrical activities of the heart is recorded
  • Willem Einthoven is called the Father of ECG

Electrocardiographic (ECG) Grid

  1. Duration:
    • Duration of different waves denoted by Vertical lines
    • Interval between 2 thick lines (5 mm) = 0.2 second
    • Interval between 2 thin lines (1 mm) = 0.04 second
  2. Amplitude:
    • Amplitude of ECG wave denoted by Horizontal lines
    • Interval between 2 thick lines (5 mm) = 0.5 mV
    • Interval between 2 thin lines (1 mm) = 0.1 mV
  3. Speed of the Paper: 25 mm per second (normally) or 50 mm per second (high heart rate)

Waves of Electrocardiogram

waves of electrocardiogram
  1. P Wave
    • P wave is the positive wave and 1st wave in ECG
    • It is produced due to the Atrial Depolarization
    • Duration - 0.1 second
    • Amplitude - 0.1 to 0.12 mV
  2. QRS Complex
    • It is also called Initial Ventricular Complex
    • Q wave is small negative wave, continued as tall R wave
    • R wave is positive wave, followed by small negative S wave
    • QRS Complex is produced due to Ventricular Depolarization
    • Duration - 0.08 to 0.10 seconds
    • Amplitude
      • Q wave: 0.1 to 0.2 mV
      • R wave: 1 mV
      • S wave: 0.4 mV
  3. T Wave
    • T wave is the positive wave and final ventricular complex
    • It is produced due to Ventricular Repolarization
    • Duration - 0.2 second
    • Amplitude - 0.3 mV
  4. U Wave
    • It is rare and insignificant wave of ECG
    • It is produced due to Repolarization of papillary muscles

Interval and Segments of ECG

  1. P - R Interval
    • Interval between onset of P wave and onset of Q wave
    • Signifies Atrial Depolarization and conduction of impulses through AV nodes
    • Duration - 0.18 second
  2. Q - T Interval
    • Interval between onset of Q wave and end of T wave
    • Signifies electrical activity in Ventricles
    • Duration - 0.4 to 0.42 seconds
  3. S - T Interval
    • Interval between end of S wave and onset of T wave
    • It is Isoelectric
    • Duration - 0.08 second
  4. R - R Interval
    • Interval between 2 consecutive R waves
    • Signifies the duration of 1 Cardiac CycleInterval between 2 consecutive R waves

ECG Leads

einthoven traingle of ECG
  1. Surface of body is connected to the ECG machine by means of 2 electrodes called ECG lead
  2. ECG leads are of 2 types: Bipolar and Unipolar leads
  3. Einthoven's Triangle: Electrodes are fixed on the limbs (right arm, left arm, left leg) and the heart is in the center of an imaginary equilateral triangle drawn by connecting the roots of these 3 limbs
  4. Bipolar Leads known as standard limb leads where 2 limbs are connected, standard limbs are of 3 following types
    • Lead 1 is obtained by connecting right arm and left arm, where right arm is connected to negative terminal and left arm is connected to positive terminal
    • Lead 2 is obtained by connecting right arm and left leg, where right arm is connected to negative terminal and left leg is connected to positive terminal
    • Lead 3 is obtained by connecting left arm and left leg, where left arm is connected to negative terminal and left leg is connected to positive terminal
  5. Unipolar Leads are of 2 types
    • Unipolar Limb Lead
    • Unipolar Chest Lead