ECGs

• P wave = depolarisation (ejection) of the atria
• PR interval = impulse delay in AV node
• QRS complex = depolarisation (ejection) of the ventricles
• ST segment = ventricular diastole
• T wave = repolarisation of ventricles
• T wave:

  • Positive in leads I, II and V3-V6
  • Always inverted in aVR
• Normal intervals:

  • PR interval = 120-220 ms = 3-5 small squares
  • QRS complex = <120 ms = <3 small squares
  • QT interval = 9-11 small squares
  • QT in men = 350-440 ms
  • QT in women = 350-460 ms
• Septal leads = V1-V2
• Anterior leads = V3-V4
• Lateral leads = I, aVL, V5-V6
• Inferior leads = II, III and aVF
• Anterior MI:

  • Occlusion of the LAD
  • ST elevation in precordial leads V1-V4
  • Reciprocal ST depression in the inferior leads III and aVF
• Lateral MI:

  • LAD and circumflex artery (mostly)
  • ST elevation in I, aVL and V5-V6
  • Reciprocal ST depression in the inferior leads
• Inferior MI:

  • RCA or circumflex
  • ST elevation in leads II, III and aVF
  • Reciprocal ST depression in aVL and I