From the Guidelines
The downward deflection in lead II and upward deflection in aVR despite correct electrode placement is likely due to a lead switch, specifically a transposition of the left and right arm lead wires, which can result in inversion of limb lead I, and a switch of leads II and III, as well as a switch of leads aVR and aVL, as described in the study by the American Heart Association electrocardiography and arrhythmias committee 1. This can be recognized by an alert technician or correctly interpreted by the reviewing physician, particularly when previous ECGs are available.
- Key characteristics of this lead switch include:
- Inversion of limb lead I
- Switch of leads II and III
- Switch of leads aVR and aVL
- No changes in the precordial leads
- To confirm the diagnosis, suspected lead switches may be confirmed by reference to a prior or subsequent tracing with correct lead placement, as suggested by the study 1.
- It's essential to distinguish this lead switch from other conditions, such as dextrocardia, which can produce similar ECG patterns, and to evaluate the patient for any associated cardiac abnormalities.
- The study by the American Heart Association electrocardiography and arrhythmias committee 1 provides guidance on the recognition and interpretation of lead switches, and emphasizes the importance of correct electrode placement and lead wiring to ensure accurate ECG recordings.