Electrocardiogram

 

  • When any muscles are stimulated electrical changes take place.
  • Body fluids are good electrical conductors (weak electrolyte solution). Thus the body can be considered Volume Conductor.
  • By placing electrodes over the body one can record these electrical changes - Electrocardiogram (ECG).
  • An ECG trace is obtained by placing one electrode on the body (ACTIVE or EXPLORING Electrode) and another electrode placed at zero potential or ground (INDIFFERENT Electrode).
  • A depolarisation wave moving towards the active electrode produces a POSITIVE DEFLECTION on the trace while if it moves away fromt he active electrode it produces a NEGATIVE DEFLECTION.
  • A repolarisation wave produces the opposite effect.
  • AN ELECTRICAL POTENTIAL IS RECORDED FROM THE BODY SURFACE ONLY DURING THE SPREAD OF DEPOLARISATION OR REPOLARISATION.