This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Anatomy
[{'content': 'All of the following statements are true about quinidine except: \nSelect and explain. \nA. It blocks myocardial Na+ channels primarily in the open state, B. It has no effect on myocardial K+ channels, C. It produces frequency dependent blockade of myocardial Na+ channels, D. It delays recovery of myocardial Na+ channels', 'role': 'user'}, {'content': 'Answer: B \nExplanation: (Ref: KDT 6/e p511, 512) Quinidine is a class I antiarrhythmic agent. It blocks Na+ channels in the open state and also delays the recovery of these channels. Blockade by these antiarrhythmic agents is frequency dependent. Class Ia antiarrhythmics, in addition blocks myocardial K+ channels also.', 'role': 'assistant'}]