In a patient with a large pericardial effusion and tamponade physiology, which ECG finding is most characteristic?

In a patient with a large pericardial effusion and tamponade physiology, which ECG finding is most characteristic?

• A. Electrical alternans with sinus tachycardia
• B. Torsades de pointes
• C. U waves
• D. Peaked T waves

Answer: (A)

The key idea is that a large pericardial effusion causing tamponade physiology makes the heart bobbing in the fluid produce beat-to-beat changes in the electrical activity. This swinging motion leads to electrical alternans, where the amplitude of the QRS complexes alternates with each beat. At the same time, compensatory sympathetic stimulation from reduced cardiac output often causes a rapid, regular rhythm—sinus tachycardia. So the combination of electrical alternans with sinus tachycardia is the most characteristic ECG pattern in tamponade. Other options describe patterns linked to different problems: torsades de pointes is a rotating, polymorphic ventricular tachycardia associated with a prolonged QT interval; U waves appear with hypokalemia or other metabolic disturbances; peaked T waves occur with hyperkalemia. These do not fit the typical ECG picture of large effusion with tamponade.

The key idea is that a large pericardial effusion causing tamponade physiology makes the heart bobbing in the fluid produce beat-to-beat changes in the electrical activity. This swinging motion leads to electrical alternans, where the amplitude of the QRS complexes alternates with each beat. At the same time, compensatory sympathetic stimulation from reduced cardiac output often causes a rapid, regular rhythm—sinus tachycardia. So the combination of electrical alternans with sinus tachycardia is the most characteristic ECG pattern in tamponade.

Other options describe patterns linked to different problems: torsades de pointes is a rotating, polymorphic ventricular tachycardia associated with a prolonged QT interval; U waves appear with hypokalemia or other metabolic disturbances; peaked T waves occur with hyperkalemia. These do not fit the typical ECG picture of large effusion with tamponade.