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
Electric alternans is seen in 
Select and explain. 
A. Cardiac tamponade, B. Restrictive cardiomyopathy, C. Constrictive pericarditis, D. Right ventricular infract
A: Cardiac tamponade
Answer: A: Cardiac tamponade 
Explanation: Rrf Harrison 19 th ed pg 1573 There may be reduction in ampli- tude of the QRS complexes, and electrical alternans of the P, QRS, or T waves should raise the suspicion of cardiac tamponade . the features that distinguish acute cardiac tampon- ade from constrictive pericarditis.