ECG changes in healthy individuals

ECG changes in an ECG of an healthy individual:

• sinus arrythmia - this is a beat-to-beat variation in heart rate that depends on respiration
  
  
• PR interval - the normal PR interval is 120 (3 little squares) to 200 ms (5 little squares)
  
  
• cardiac axis - a normal cardiac axis means upright QRS complexes in leads 1, 2 and generally 3
  
  
• QRS complex - the width of the QRS complex is less than 120 ms
  
  
• the maximum height of R plus S is less than 35 mm, the maximum height of an R wave is 25mm
  
  
• there is a gradual progression in height of the R wave from V1 to V6
  
  
• ST segments are isoelectic - this means that the ST segment is at the ECG baseline
  
  
• T waves - there may be inversion in V1 and occasionally V2; the T waves in VR are generally inverted

Reference:

• Hampton J. Update (8/7/99), 79-82