Saturday, October 21, 2017


File:Ecg.png - Wikimedia Commons

P wave

  • Positive wave
  • Shape is up rounded deflection
  • Cause: Depolarisation of atrial musculature.
  • Duration: 0.1 sec
  • Intensity: 0.1-0.12 mV
  • Represents functional activity of atria.

Clinical Aspects:
  1. Mitral stenosis: left atrium is hypertrophied and P wave is larger and prolonged.
  2. Tricuspid stenosis: Right atrium is hypertrophied and P wave is taller but there is no change (normal) duration.
  3. Atrial fibrillation: P wave disappears and is replaced by fine irregular oscillations.
  4. Ectopic Pacemaker: (reverse) The impulses are sent from AV node to SA node.


  • Q wave is often absent.
  • Cause: Ventricular Depolarisation.
  • Duration: 0.08 sec ( less than P wave)
  • Intensity: 0.1 mV to 0.2 mV ( amplitude is more)
  • R wave is 1 mV
  • S wave is 0.4 mV
  • Total Intensity is 1.5 mV to 1.6 mV

Clinical Aspects
  1. Deep Q wave: more than 0.2 mV. This is seen Myocardial Infarction.
  2. Tall R wave: more than 0.1 mV. This is seen in ventricular hypertrophy.
  3. Low Voltage QRS Complex:  This is related to hormones and pericardial fluid. Hypothyroidism and Pericardial fluid around the heart.
  4. QRS COMPLEX: Prolonged in bundle branch block.

T wave

  • Cause: Ventricular Repolarization.
  • It’s positive wave because the direction of Ventricular repolarization is opposite to depolarization.
  • Duration: 0.27
  • Intensity: 0.3 mV

Clinical Aspects

  1. Flattened T wave: old age.
  2. Height increases: during exercise.
  3. Inverted T wave: this is seen in myocardial infarction.
  4. Tall and peaked T wave:  Hyperkalaemia.

U wave
  • Positive round wave
  • Repolarization of papillary muscled
  • Duration: 0.08 sec
  • Intensity: 0.2 mV
  • Rarely seen
  • Prominent in hypokalaemia.

P R interval

  • Onset of P wave to onset of QRS complex (PQ interval)
  • Represents AV conduction time.
  • Duration: 0.12 to 0.21 sec

Clinical Aspects

  1. Prolonged PR interval: AV conduction block.

J Point

  • The meeting point of QRS complex with ST segment.
  • It represents the end of Depolarisation and beginning of repolarization.
  • At this point, no current flows around heart.

I hope this helped you :))  Have a good day!

1 comment:

  1. Does the current of injury flow at the j point or after it ??


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