B  

Lidocaine is a class Ib anti-arrhythmic that blocks fast Na⁺ channels (especially in depolarized or ischemic tissue), thereby lowering the slope of phase 0 and shortening action-potential duration. This reduction in Na⁺ influx diminishes myocardial excitability without speeding conduction or pacemaker activity, accounting for its anti-arrhythmic effect [Güler 2023, PMID 37781966; Kodama 1986, PMID 2434686].