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Reference Text
Mechanism: Class I antiarrhythmics block voltage-gated Na+ channels. Clinically useful agents bind during open/inactivated states; dissociation occurs during resting state.
Use Dependence: Tissues undergoing frequent depolarization (fast HR) are more susceptible to blockage because channels spend more time in open/inactivated states.
Class IB (e.g., Lidocaine): Weakest binding. Fast dissociation. Selective for ischemic myocardium because elevated resting potential delays transition from inactivated to resting state.
Binding Strength Order: Class IC (Strongest) > Class IA > Class IB (Weakest). Remember "Cab Driver" (C > A > B).