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
[{'content': 'Electrical alternans in ECG is characteristic of \nSelect and explain. \nA. Severe bronchial asthma, B. Pericardial effusion, C. Severe LVF, D. AR', 'role': 'user'}, {'content': 'Answer: B \nExplanation: 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', 'role': 'assistant'}]