This 73-year-old woman has been referred by her family physician because of angina during moderate exertion. She has been known to have a congenital cardiac abnormality:

The computer’s diagnostic program suggests “arm lead reversal”, however, dextrocardia is the most likely diagnosis. In favor of dextrocardia:

• the P and QRS are negative in 1 and aVL and positive in aVR
• the P wave has a +/- identical pattern from V1 to V6
• the QRS has the same rS pattern and decreasing voltage from V1 to V6

In view of the history of angina, the presence of a positive T wave in lead I suggests lateral ischemia (we would expect a negative T in uncomplicated dextrocardia). An ECG tracing should be obtained with reversal of the arm lead and right chest leads recording.

A repeat ECG confirmed the presence of dextrocardia. The following ECG was obtained with reversal of the arm lead and right chest leads:

• Normal sinus rhythm
• Left anterior fascicular block
• Possible lateral infarction (q wave in leads I and aVL)
• T wave abnormality, consider anterolateral ischemia

A myocardial perfusion scan demonstrated anterior myocardial infarction and peri-infarction ischemia.