[[Image:cableReversal1.png|thumb|Right and left arm lead reversal can be distinguished from the (much rarer) dextrocardia by looking at the precordial R wave progression.]]
[[Image:cableReversal2.png|thumb|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.]]
[[Image:dextrocardia.jpg|thumb|A patient with dextrocardia (and previous inferior myocardial infarction)]]
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:
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)
artifacts (disturbances) can have many causes. Common causes are: *Movement *Electrical interference