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ECG changes in healthy individuals

Last reviewed dd mmm yyyy. Last edited dd mmm yyyy

Authoring team

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


  • Hampton J. Update (8/7/99), 79-82

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