In a patient in their late 80s with chest pain and a prior left bundle branch block, what does an inverted QRS in lead II and an upright QRS in lead aVR on the ECG indicate?

ECG Lead Reversal: Immediate Technical Error Recognition Required

The pattern of inverted QRS complexes in lead II combined with upright QRS complexes in lead aVR strongly indicates limb lead reversal, specifically right arm and right leg electrode misplacement, rather than a true cardiac pathology. This is a technical artifact that must be recognized immediately to avoid misdiagnosis of myocardial infarction in this elderly patient with chest pain.

Why This Represents Lead Reversal

The key diagnostic features pointing to technical error include:

• Lead II showing inverted QRS: During normal sinus rhythm, lead II should always show predominantly positive P waves and QRS complexes because it views the heart's electrical activity along the normal depolarization vector. Inversion suggests the electrodes are viewing the heart from an abnormal angle 1.

• Lead aVR showing upright QRS: In normal electrode placement, aVR views the heart from the opposite direction of normal depolarization and should show negative deflections. When aVR appears "normal" (upright), this is paradoxically abnormal 1.

• The specific pattern: Inversion of right arm and right leg leads causes marked low voltage in lead II due to the shortened "distance" between the misplaced electrodes, and creates pathologic-appearing Q waves and T wave inversions in up to 37% and 51% of cases respectively 1.

Critical Pitfall in This Clinical Context

This technical error is particularly dangerous in your patient because:

1. Age and symptoms: An octogenarian with chest pain and known LBBB has high pretest probability for acute coronary syndrome
2. False MI diagnosis: Lead reversal frequently produces pathologic Q waves and ischemic T wave changes that can mimic myocardial infarction 1
3. Pre-existing LBBB: The baseline conduction abnormality already makes MI diagnosis challenging, and adding a technical artifact compounds the difficulty

Immediate Action Required

Before making any clinical decisions about acute coronary syndrome, repeat the ECG with verified correct electrode placement:

• Confirm right arm electrode is on the right arm (not right leg)
• Verify lead II shows appropriate voltage and positive deflections
• Check that aVR returns to its expected negative morphology
• Compare precordial leads V1-V6: these should remain unchanged between recordings if the issue is purely limb lead reversal 1

If Lead Placement is Confirmed Correct

Only if electrode placement is verified and the pattern persists should you consider true cardiac pathology. In the context of LBBB, standard ST-segment criteria for MI are unreliable 2. The presence of LBBB causes ST-T waves to be opposite in direction to the QRS complex, which is expected 2. However, extreme axis deviation or new changes warrant urgent evaluation.

The most likely scenario remains technical error until proven otherwise through repeat ECG with meticulous electrode verification.