This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: C.V.S, Subject name: Medicine
Electrical alternans in ECG is characteristic of 
Select and explain. 
A. Severe bronchial asthma, B. Pericardial effusion, C. Severe LVF, D. AR
B: Pericardial effusion
Answer: B: Pericardial effusion 
Explanation: Electrical alternans is an electrocardiographic phenomenon defined as an alternating amplitude or axis of the QRS complexes in any or all leads. It is most commonly associated with a large pericardial effusion and impending threat of cardiac tamponade Ref Davidson 23rd edition pg 467