If a patient has a narrow-complex supraventricular tachyarrhythmia and is stable, what is the first intervention?

In the case of a stable patient experiencing a narrow-complex supraventricular tachyarrhythmia, the first intervention is to perform vagal maneuvers. These techniques aim to stimulate the vagus nerve, which can help to slow down the heart rate and potentially restore normal sinus rhythm. Vagal maneuvers are non-invasive and can be effective in terminating certain types of tachycardia, particularly those arising from atrial or nodal reentrant circuits.

Engaging in vagal maneuvers can include actions like the Valsalva maneuver or carotid sinus massage, which can enhance vagal tone and ameliorate the heart's conduction pathways. This step is typically taken before considering pharmacologic interventions or more aggressive measures like cardioversion, especially since the patient is stable and does not require immediate interventions to protect vital hemodynamics.

The other options, such as administering beta-blockers or starting IV antihypertensive therapy, may be considered later if vagal maneuvers are ineffective. Cardioversion, while a potential treatment for tachyarrhythmias, is reserved for unstable patients or cases where less invasive measures have failed. Thus, initiating vagal maneuvers represents the most appropriate first step in the