If vagal maneuvers and adenosine fail to terminate an irregular narrow tachycardia, what is the most likely underlying rhythm?

The correct answer is atrial flutter. When vagal maneuvers and adenosine fail to terminate an irregular narrow tachycardia, atrial flutter is a likely underlying rhythm due to its characteristic pattern of atrial activity, which can lead to a rapid ventricular response. Atrial flutter is typically associated with a specific reentrant circuit in the right atrium, which can create a variable ventricular rate depending on the conduction through the AV node.

In cases of atrial flutter, the regularity of the rhythm may appear more consistent than in other tachyarrhythmias like atrial fibrillation, which is characterized by chaotic electrical activity. Consequently, when the response to vagal maneuvers is ineffective, it suggests that the rhythm mechanism is not purely reliant on AV nodal conduction, pointing towards atrial flutter as a strong possibility.

Other conditions such as atrial fibrillation or supraventricular tachycardia may exhibit irregularity and can also present as narrow tachycardias, yet the failure of vagal maneuvers and adenosine tends to suggest a rhythm that does not respond typically to these interventions, which aligns more closely with the underlying mechanics of atrial flutter. While sinus tachycardia is a possible