Which drug is the first choice to treat regular narrow complex tachycardias after vagal maneuvers have failed?

Adenosine is the first choice to treat regular narrow complex tachycardias after vagal maneuvers have failed because it acts quickly to restore normal sinus rhythm by temporarily blocking the conduction through the atrioventricular (AV) node. It is particularly effective for conditions such as paroxysmal supraventricular tachycardia (SVT), where rapid electrical signals originate above the ventricles, leading to the tachycardia.

When vagal maneuvers, such as the Valsalva maneuver or carotid sinus massage, do not succeed in terminating the tachycardia, adenosine is administered as it can provide rapid and effective relief, typically within seconds, due to its short half-life. The rapid action of adenosine makes it a preferred choice in acute settings where quick restoration of normal rhythm is necessary and can help to determine the underlying rhythm on an electrocardiogram during its brief action.

While beta-blockers and calcium channel blockers may also be used in management of tachycardias, they are generally employed in situations where adenosine is either contraindicated or not immediately available, and their onset of action is slower compared to adenosine. Digoxin can be effective for controlling