Which of the following agents is classified as a negative chronotrope?

A negative chronotrope is a substance that decreases heart rate. Digoxin is well-known for its ability to exert a negative chronotropic effect by increasing parasympathetic tone to the heart and reducing the rate of electrical conduction through the sinoatrial (SA) node, which is responsible for initiating the heartbeat. This action helps to control heart rate, particularly in conditions such as atrial fibrillation, where it can be beneficial for slowing down the ventricular rate.

In contrast, other agents listed do not have this effect on heart rate; for instance, amiodarone is an antiarrhythmic that can have variable effects on heart rate depending on the situation, but it is not primarily categorized as a negative chronotrope. Epinephrine, on the other hand, is a potent stimulant that increases heart rate and myocardial contractility, making it a positive chronotrope. Atropine is used to increase heart rate, particularly in cases of bradycardia, thereby acting as a positive chronotropic agent.

The action of digoxin to decrease heart rate through vagal stimulation makes it the correct answer in this context.