Lead switches are a common mistake when ECGs are made and can lead to wrong diagnoses. Common mistakes are:
* '''Left-right arm reversals'''
this lead 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 reversals''' lead to inappropriate 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.