Which Vaughan Williams class I antiarrhythmic drug blocks fast Na+ channels with slow dissociation kinetics, prolongs the QRS duration, and is used mainly after myocardial infarction when other agents fail?
- A Quinidine ✓
- B Flecainide
- C Lidocaine
- D Mexiletine
Correct answer: A. Quinidine
Explanation
Quinidine is a class IA agent with intermediate kinetics: it slows phase 0 upstroke modestly, prolongs APD and QT, and widens QRS. It has historical use post-MI for ventricular arrhythmias though CAST-era data shifted practice away. Lidocaine and mexiletine are class IB with rapid dissociation and no QRS widening. Flecainide is class IC with very slow dissociation and marked QRS widening, but it is contraindicated after MI because of increased mortality in the CAST trial.
Reference: Katzung Basic and Clinical Pharmacology, 16th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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