Technical Problems

Author(s)	J.S.S.G. de Jong
Moderator	J.S.S.G. de Jong
Supervisor
some notes about authorship

Lead reversals

Lead switches are a common mistake when ECGs are made and can lead to wrong diagnoses. Common mistakes are:

• Left - right arm reversals. This leads to a negative complex in lead I with also a negative P wave in lead I. It is one of the most common causes of right axis deviation on the ECG!
• Arm - foot switches lead to a very small or 'far field' signal in leads II or III.
• Chest lead reversal lead to inappropiate R wave progression (increase - decrease - increase) and are often easily recognized.

Therefore any right axis or small signal in an extremity lead should be reason enough to check lead positioning. A previous ECG can be very helpful.

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  Right and left arm lead reversal can be distinguished from the (much rarer) dextrocardia by looking at the precordial R wave progression.
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  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.
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  A patient with dextrocardia (and previous inferior myocardial infarction)

More specific patterns with every lead reversal:

• 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 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 not show any R wave progression in leads V1-V6, whereas lead reversal will.

Artifacts

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

• Movement
• Electrical interference

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  Movement artifacts
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  Increasing movement artifacts in a Parkinson patient. The patient was in sinus rhythm! (which doesn't show on this short recording)
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  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.
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  Cardioversion from atrial fibrillation to sinus rhythm, with clear baseline drift.
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  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.
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  Another example of an artefact caused by an electrical appliance. The patients rhythm is regular. This strip shows 10 QRS complexes.
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  An artifact that was originally diagnosed as a VT