This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Cardiovascular system, Subject name: Pharmacology
[{'content': 'Drug of choice for paroxysmal supraventricular tachycardia is: \nSelect and explain. \nA. Verapamil, B. Diltiazem, C. Digoxin, D. Phenytoin', 'role': 'user'}, {'content': 'Answer: A \nExplanation: Verapamil decreases conduction velocity and increases the refractory period of the AV node, thus useful in PSVT. It is a CCB, Class 4 antiarrhythmic drug Adenosine and magnesium sulfate can also be used for PSVT REF: Essentials of Pharmacology KD Tripathi 8th ed.', 'role': 'assistant'}]