Scenario: A 45-year-old female executive arrived at the emergency room with complaints of substernal chest pressure and shortness of breath. She has no prior medical or surgical history, takes no medication, has a normal body mass index, and exercises regularly. Below is her 12-lead ECG obtained in the emergency room.

The ECG shows normal sinus rhythm at 99/min plus lateral ST changes (T wave inversion in V5 and V6). Although not diagnostic, it may suggest myocardial ischemia. Limb lead reversal prevents interpretation of the limb leads.

Lead reversal is frequent and has become more common as nonexperienced personnel replace trained ECG technicians.

This type of lead reversal affects all of the limb leads but lead I can be used to identify this error by checking for the following: (1) inverted QRS complex; (2) a striking Q wave; (3) inverted...

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