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.
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
Image:ECG_Parkinson.png|Increasing movement artifacts in a Parkinson patient. The patient was in sinus rhythm
! (which doesn't show on this short recording)
Image:BaselineDrift.png|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.
Image:cardioversion_from_afib.jpg|Cardioversion from atrial fibrillation to sinus rhythm, with clear baseline drift.
Image:electric_noise_ecg.png|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|atrial fibrillation]].
Image:electric_noise_ecg2.jpg|Another example of an
artefact caused by an electrical appliance. The patients rhythm is regular. This strip shows 10 QRS complexes.
File:DVA2162.jpg|An artifact that was originally diagnosed as a VT