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': 'Cardiac tamponade causes pulsus: \nSelect and explain. \nA. Alternans, B. Bigemini, C. Paradoxus, D. Parvus', 'role': 'user'}, {'content': 'Answer: C \nExplanation: Ans: c (Paradoxus) Ref: Harrisons, 16th ed, p. 1416; 17th ed, p. 1491Clinical signs in cardiac tamponade - pulsus paradoxus, prominent x descent in JVPECG changes - low ECG voltage, electrical alternans. RVDC feature in echoNotesFreidrichs sign - Rapid fall (steep Y descent) and rise of JVP seen in constrictive pericarditis and tricuspid regurgitation.', 'role': 'assistant'}]