A 58-year-old man develops sustained ventricular tachycardia 6 hours after an acute anterior myocardial infarction. He is hemodynamically stable. Which property makes lidocaine particularly suited to treating ventricular arrhythmias in this setting?
- A It shows marked use-dependence and preferential block of depolarized, ischemic tissue ✓
- B It selectively accumulates in normal well-perfused myocardium
- C It markedly prolongs the effective refractory period in ventricular muscle
- D It slows AV nodal conduction, preventing ventricular escape rhythms
Correct answer: A. It shows marked use-dependence and preferential block of depolarized, ischemic tissue
Explanation
Ischemic myocytes are depolarized and fire rapidly, favoring the open and inactivated sodium channel states to which lidocaine binds avidly. This state- and frequency-dependent block concentrates its action on ischemic tissue with little effect on normal conduction, giving it high efficacy against post-infarction ventricular arrhythmias at low risk of depressing healthy myocardium. Lidocaine does not meaningfully prolong refractory period, distinguishing class IB from class IA and III agents.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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