What is the most appropriate pharmacologic agent for initial management of AV nodal reentrant tachycardia in an 8-year-old?

The most appropriate pharmacologic agent for the initial management of AV nodal reentrant tachycardia (AVRT) in an 8-year-old is adenosine. Adenosine works by temporarily blocking conduction through the atrioventricular (AV) node, which can effectively interrupt the reentrant circuit responsible for AVRT. This rapid action makes it a first-line agent for this particular type of tachycardia, as it provides a quick termination of the arrhythmia.

Adenosine's safety profile, efficacy in terminating paroxysmal supraventricular tachycardia, and ability to quickly restore normal sinus rhythm make it the preferred choice in pediatric patients. The rapid onset and short duration of action reduce the risk of prolonged effects, which is particularly important in children.

While other options may be used in different contexts of cardiac management, such as digoxin for atrial fibrillation or heart failure, or diltiazem for rate control in other supraventricular tachycardias, adenosine's specific mechanism of action and rapid effect align perfectly with the needs of managing AVRT. Lidocaine, primarily utilized in ventricular arrhythmias, is not indicated for AVRT, especially in a pediatric scenario