08 Respiration and Circulation - part 16 - Electrocardiogram

 

08 Respiration and Circulation - part 16 - Electrocardiogram


Electrocardiogram:
  • Graphical recording of electrical variations detected at the surface of body during their propagation through the wall of heart is electrocardiogram (ECG). 
  • This recording may be in the form of printout or onscreen display. 
  • The instrument used for this recording is the ECG machine or electrocardiograph.
  • This instrument detects and amplifies the signals.
  • Various electrodes are used for recording of signals. 
  • Four electrodes are positioned on limbs; two on arms and two on legs. These are limb electrodes. 
  • Six electrodes are positioned on chest. These are chest electrodes.
  • In a normal record, three different waves are recognized as P-wave, QRS complex and T-wave. 
P-wave :

  • Is a small upward deflection from baseline of graph. 
  • It represents the atrial depolarization. 
QRS complex : 
  • Starts as a slight downward deflection from baseline, continues as sharp and large upright wave and ends as a downward wave. 
  • QRS complex represents the ventricular depolarization.
T-wave :
  • Is small, wide and upwardly elevated wave. 
  • It represents the ventricular repolarization.
ECG helps to  - 
  1. Diagnose the abnormality in conducting pathway, enlargement of heart chambers, damages to cardiac muscles, reduced blood supply to cardiac muscles andcauses of chest pain. 
  2. A physicial can find out the defect in the heart by examining the wave pattern and the time interval betwen them.

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