Technical Problems

Lead reversals

Right and left arm lead reversal can be distinguished from the (much rarer) dextrocardia by looking at the p-wave.

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.

Sometimes an ECG is 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 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 od leads aVR and aVF
  • inversion of lead III
• right arm and left leg:
  • inversion of laeds 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, wheras lead reversal will not.

Artefacts

Movement artefacts

Increasing movement artefacts in a Parkinson patient. The patient was in sinus rhythm! (which doesn't show on this short recording)

Baseline drift. The amplifier in the ECG machine has to re-find the 'mean'. This often occurs right after lead connection and after electric cardioversion.

Electrical interference from a nearby electrical appliance. A typical example is a 100 Hz background distortion from fluorescent lights. Not to be confused with atrial fibrillation.

Another example of an artefact caused by an electrical appliance. The patients rhythm is regular. This strip shows 10 QRS complexes.

Artefacts (disturbances) can have many causes. Common causes are:

• Movement
• Electrical interference