Which of the following anti-arrhythmic drug decreases the action potential duration in Purkinje fibers?
Ans. d (Lignocaine) (Ref. KDT pharmacology 6th/pg.513)# The most prominent cardiac action of lidocaine is suppression of automaticity in ectopic foci. Enhanced phase-4 depolarization in partially depolarized or stretched PFs, and after depolarizations are antagonized, but SA node automaticity is not depressed.# The rate of 0 phase depolarization and conduction velocity in A-V bundle or ventricles is not decreased. Lidocaine decreases APD in PF and ventricular muscle, but has practically no effect on APD and ERP of atrial fibres. Atrial reentry is not affected. However, it can suppress reentrant ventricular arrhythmias either by abolishing one-way block or by producing two way block.# Lidocaine is a blocker of inactivated Na+ channels more than that of open state.Vaughan-Williams CLASSIFICATION OF ANTIARRHYTHMIC DRUGSIA# |Vmax at all heart rates and increases action potential duration# e.g., quinidine, procainamide, disopyramideIB# Little effect at slow rates on Vmax in normal tissue; | Vmax in partially depolarized ceils with fast response action potentials# Effects increased at faster rates# No change or | in action potential duration# e.g., lidocaine, phenytoin, tocainide, mexiletineIC# |Vmax at normal rates in normal tissue# Minimal effect on action potential duration,# e.g., flecainide, propafenone, moricizineClass II# |SA nodal automaticity, increase AV nodal refractoriness, and |AV nodal conduction velocity# Antisympathetic agents, e.g., propranolol and other ss-adrenergic blockersClass III# Agents that prolong action potential duration in tissue with fast-response action potentials# e.g., bretylium, amiodarone, sotalol, ibutilide, dofetilideClass IV# Calcium (slow) channel blocking agents# | conduction velocity and increase refractoriness in tissue with slow-response action potentials# e.g., verapamil, diltiazemDrugs that cannot be classified by this schema# Digitalis# Adenosine
Quinidine
Flecainide
Amiodarone
Lignocaine
C.V.S