ECG PR Interval

• If present, is the PR interval normal?

  • PR interval should be no longer than 0.2 second (1 large square)
  • PR interval shows how long the impulse is held at the atrioventricular node for
  • if the PR interval is longer than this, we call it a first degree heart block

  
• If present, is the PR interval normal? - 2nd Degree heart blocks

  • top ECG: Mobitz Type 1 ( Wenckebach)
  • PR interval increases in size, then skips a QRS complex, and then decreases in size back to normal
  • bottom ECG: Mobitz Type 2
  • PR interval is continuously prolonged, then skips a QRS complex
  • more of a concern than type 1 as it can lead to third degree heart block
  • treated with a pacemaker

  
• If present, is the PR interval normal?

  • in this ECG there seems to be no association between the P wave and QRS complex
  • called a 3rd degree heart block
  • the atria and ventricle seem to be out of sync
  • HR is around 30 bpm as the impulse is blocked, so the left ventricle has to become the main pacemaker and the impulse is generated in the purkinje fibres
  • pacemaker needs to be inserted ASAP to resynchronise the atria and ventricles

  
• What causes heart/AV blocks?

  • medication - beta-blockers
  • myocardial ischaemia - caused by lack of blood/oxygen to the heart
  • myocardial infarction - necrosis of tissue made up of pacemaker cells
  • cardiac surgery (valve surgery)
  • changes associated with aging
  • congenital abnormalities