What is electrical alternans and in what condition is it classically seen?

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Multiple Choice

What is electrical alternans and in what condition is it classically seen?

Electrical alternans is a beat-to-beat change in the QRS complex amplitude (and sometimes its axis) on the ECG. This happens when the heart swings within a large pericardial effusion, so the electrical vector relative to the chest leads changes with each beat. The classic setting is cardiac tamponade due to a large effusion, where this swinging motion produces the alternating QRS voltage you see. This differs from a normal, stable ECG in a healthy person, from ischemic changes that involve T waves or ST segments rather than QRS voltage, and from atrial fibrillation which causes an irregular rhythm rather than alternating depolarization amplitude. If you observe electrical alternans, it should raise suspicion for a significant pericardial effusion with potential tamponade.

Electrical alternans is a beat-to-beat change in the QRS complex amplitude (and sometimes its axis) on the ECG. This happens when the heart swings within a large pericardial effusion, so the electrical vector relative to the chest leads changes with each beat. The classic setting is cardiac tamponade due to a large effusion, where this swinging motion produces the alternating QRS voltage you see. This differs from a normal, stable ECG in a healthy person, from ischemic changes that involve T waves or ST segments rather than QRS voltage, and from atrial fibrillation which causes an irregular rhythm rather than alternating depolarization amplitude. If you observe electrical alternans, it should raise suspicion for a significant pericardial effusion with potential tamponade.

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