A 69-year-old man with known symptomatic coronary artery disease is admitted for angioplasty of his circumflex artery:

• Suspect lead error (Right Arm – Left Arm Reversal)
• Sinus rhythm, left bundle branch block

Please, repeat the ECG.

In favor of Right arm – Left arm reversal:

• Lead I looks like lead V6 upside down (negative P and QRS)
• aVR has positive P and QRS, aVL negative P and QRS (which is the opposite of we expect)

A second ECG is recorded, with special attention to correct lead placement:

• The previous tracing had been incorrectly recorded (right arm – left arm reversal)
• Sinus rhythm
• 1st degree AV block
• Left bundle branch block