<prompt> Ibutilide acts byBlockade of Na currentInterference with the action of catecholamines at the b-adrenergic receptorDelay of repolarization due to inhibition of K currentInterference with calcium conductance  <response>: Ibutilide is a class III antiarrhythmic drug.The classes of antiarrhythmic action are:- Class I, Local anaesthetic effect due to blockade of Na currentClass I antiarrhythmics have been fuher subdivided based on the kinetics and potency of Na channel bindingClass Ia agents quinidine, procainamide are those with moderate potency and intermediate kinetics;Class Ib agents lidocaine, mexiletine are those with low potency and rapid kinetics; and Class Ic drugs flecainide, propafenone are those with high potency and the slowest kinetics.Class II: Interference with the action of catecholamines at the b-adrenergic receptor Atenolol, Propranolol, Esmolol, MetoprololClass III: Delay of repolarization due to inhibition of K current or activation of depolarizing current Amiodarone, Sotalol, Ibutilide, DofetilideClass IV: Interference with calcium conductance Diltiazem, VerapamilHarrison 19e pg: 273e-6 