Sometimes an ECG is not made properly. Mistakes do happen and leads can be switched. Always remain careful to check this or you might come to the wrong conclusions. One of the most common mistakes is to switch the right and left arm. This will result in negative complexes in I, indicating a right axis deviation!

Common mistakes are reversal of:

• Right leg and right arm:
  • Hardly seen any signal in lead II.
• Right and left arm electrodes;
  • Reversal of leads II and III
  • Reversal of leads aVR and aVL
• Left arm and left leg:
  • Reversal of leads I and II
  • Reversal of leads aVR and aVF
  • Inversion of lead III
• Right arm and left leg:
  • Inversion of leads I, II and III
  • Reversal of leads aVR and aVF

It is possible to distinguish lead reversal and dextrocardia by watching the precordial leads. Dextrocardia will show an R wave inversion, whereas lead reversal will not.^[1]

• 
  An example of reverse lead placement
• 
  Right and left arm lead reversal can be distinguished from the (much rarer) dextrocardia by looking at the precordial R wave progression.
• 
  Right arm and left leg lead reversal. Lead II now measures the signal between the left and right leg, which is remote from the heart.

• ECGpedia: Course for interpretation of ECG
• The whole ECG – A basic ECG primer
• 12-lead ECG library
• Simulation tool to demonstrate and study the relation between the electric activity of the heart and the ECG
• ECG information from Children’s Hospital Heart Center, Seattle
• ECG Challenge from the ACC D2B Initiative
• National Heart, Lung, and Blood Institute, Diseases and Conditions Index
• A history of electrocardiography
• EKG Interpretations in infants and children

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