Adenosine antiarrhythmic action

Adenosine reduces heart rate and AV conduction, although it is not a calcium antagonist. It is administered intravenously for the acute treatment of paroxysmal supraventricular tachycardia. Adenosine displays a rapid onset and short duration of action. Apart from its antiarrhythmic activity it is also a vasodilator, in particular in the coronary system. 

For example, amiodarone shares all four classes of action. Drugs are usually discussed according to the predominant class of action. Certain antiarrhythmic agents, eg, adenosine and magnesium, do not fit readily into this scheme and are described separately. 

As noted above, the antiarrhythmic drugs can modify impulse generation and conduction. More than a dozen such drugs that are potentially useful in treating arrhythmias are currently available. However, only a limited number of these agents are clinically beneficial in the treatment of selected arrhythmias. For example, the acute termination of ventricular tachycardia by lidocaine or supraventricular tachycardia by adenosine or verapamil are examples in which antiarrhythmic therapy results in decreased morbidity. In contrast, many of the antiarrhythmic agents are now known to have lethal proarrhythmic actions, that is, to cause arrhythmias. 

The hypotensive effects of adenosine receptor agonists probably are of limited (commercial) use, in view of the overwhelming number of therapeutic strategies already in clinical practice. On the contrary, the potentially beneficial metabolic, antiarrhythmic and CNS effects also elicited by these compounds are confounded by the cardiovascular actions. Thus, the clinical development of an adenosine receptor agonist as a novel antipsychotic was discontinued due to its cardiovascular toxicity [6]. 

The only antiarrhythmic agent that consistently alters the resting potential of the AV node is adenosine. It apparently activates Ij, potassium channels in the AV node, thus forcing the membrane potential closer to the Nernst potassium potential thus, adenosine significantly hy-perpolari2Ks this tissue, preventing the conduction of action potentials. The answer is (A). 

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