This 50-year-old man with ischemic cardiomyopathy is seen in the anaesthesia clinic in preparation for cardiac surgery:

• Suspect lead placement error (Left Arm-Left Leg Lead Reversal) in patient with left bundle branch block

Comments: The interpretation of the computerized ECG program was: “Ectopic atrial rhythm – Non-specific intraventricular block”. The diagnosis of left arm – left leg reversal  is missed always by computerized programs and often by physicians (unless a previous ECG is available).

Leads I is actually lead II, (and vice-versa). In this case left arm – left leg cable reversal should be suspected because:

1. lead II and V6 show the typical pattern of left bundle branch block, while the QRS is negative in lead I and and has a wide monophasic R in lead II
2. the P wave is wider and taller in lead I than in lead II. This the opposite of what we would expect: if the pattern of the P wave in I and II is different, the P is usually wider and/or taller in lead II.

As the unusual pattern of ECG 1 is recognized, a new tracing is recorded with correct lead cables placement:

• Sinus rhythm
• Left axis deviation
• Left bundle branch block
• The previous ECG had been incorrectly recorded (lead placement error, left arm-left leg lead reversal)