Final answer:
The next appropriate action would be to administer adenosine.
Step-by-step explanation:
In this case, the patient is experiencing narrow complex tachycardia, specifically supraventricular tachycardia, with a heart rate of 220 bpm. Vagal maneuvers, which are typically used to slow down the heart rate, have not been successful in this case. Therefore, the next appropriate action would be to administer a medication called adenosine, which is commonly used to treat supraventricular tachycardia. Adenosine works by blocking the electrical conduction in the heart, which can help restore a normal heart rhythm.