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24. The correct answer is D.
The patient has a ventricular tachycardia as indicated by the electrocardiogram: the appearance of a wide-complex ventricular tachycardia with a rate of 126 beats per minute. Propranolol is a Type II antiarrhythmic agent that acts by decreasing SA node automaticity, increasing AV nodal refractoriness, and decreasing AV nodal conduction velocity. Propranolol is indicated for the treatment of ventricular tachycardias, supraventricular arrhythmias, and for slowing the ventricular rate during atrial fibrillation and atrial flutter.

Amiodarone (choice A) is a Type III antiarrhythmic that acts by prolonging the action potential duration in tissue with fast-response action potentials. Amiodarone is indicated for treatment of refractory ventricular arrhythmias that are unresponsive to other antiarrhythmics.

Disopyramide (choice B) is a Type IA antiarrhythmic that reduces the maximal velocity of phase 0 depolarization by blocking the inward sodium current in tissue with fast-response action potentials. It also increases the action potential duration. Disopyramide is indicated for the treatment of atrial and ventricular extrasystoles and atrial and ventricular tachyarrhythmias.

Lidocaine (choice C) is a Type IA antiarrhythmic that reduces the maximal velocity of phase 0 depolarization by blocking the inward sodium current in tissue with fast-response action potentials. Lidocaine is indicated for the treatment of atrial and ventricular extrasystoles, and atrial and ventricular tachyarrhythmias.

Verapamil (choice E), a Type IV antiarrhythmic agent, blocks calcium channels, thereby decreasing conduction velocity and increasing refractoriness in tissue with slow-response action potentials. Verapamil is indicated for the treatment of atrial fibrillation and flutter as well as other atrial tachycardias.

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