Which antiarrhythmic is an oral potassium channel blocker used to maintain sinus rhythm in AF?

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Dofetilide is the pure potassium channel blocker (IKr) used to maintain sinus rhythm in atrial fibrillation. It acts by prolonging the repolarization phase, helping prevent reentry circuits that sustain AF. It’s taken orally and is specifically chosen for rhythm maintenance after cardioversion because of its selectivity for the potassium channels. Initiation must occur in a monitored setting due to the risk of QT prolongation and torsades de pointes, with attention to electrolytes and renal function.

Amiodarone also prolongs repolarization but is a multichannel blocker, not a pure potassium channel blocker. Quinidine sulfate is mainly a sodium channel blocker with some potassium effects, and sotalol combines beta-blockade with potassium channel blockade but is not a pure potassium channel blocker. Thus, dofetilide best fits the description.