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
Which of the following is not a component of classical triad of ECG changes in pericardial effusion with cardiac tamponade? 
Select and explain. 
A. Sinus tachycardia, B. Prolonged ST segment, C. Low voltage QRS complex, D. Electrical alternans
B: Prolonged ST segment
Answer: B: Prolonged ST segment 
Explanation: Ans. B. Prolonged ST segmentProlonged ST segment is not a part of classic triad of ECG findings for pericardial effusion with cardiac tamponade.* Classical triad of ECG changes in pericardial effusion with cardiac tamponade includes:- Sinus tachycardia- Low QRS voltages- Electrical alternans (best seen in leads V3 and V4 in this case; arrows)* This triad is highly specific for pericardial effusion, usually with tamponade physiology, but of limited sensitivity