ECG electrode reversals: An opportunity to learn from mistakes.

An ECG with an "odd" appearance may raise the suspicion that ECG recording electrodes may have been reversed. Odd appearances include unexpected Q-waves or R-waves, markedly isoelectric leads, and abrupt changes from previous ECGs. A few examples of ECG electrode reversal provide the opportunity to review some fundamental principles of ECG recording. Some ECG electrode reversals will invert the QRS complex recorded in a lead. Other ECG leads may be affected in a manner that initially may seem unexpected. These patterns may be understood upon reviewing the genesis of the "unipolar" leads, particularly the "augmented" leads. Recording an ECG between electrodes placed on the two legs will produce a nearly isoelectric tracing. Elucidation of electrode reversals is often less difficult than it seems, may present an enjoyable intellectual challenge, and provides insight into the process of ECG recording.