A 30-year-old woman is admitted to the Emergency Department following the acute onset of palpitations. An ECG shows a narrow complex tachycardia.. Intravenous adenosine 12 mg

A 30-year-old woman is admitted to the Emergency Department following the acute onset of palpitations. Blood pressure is 124/84 mmHg and her pulse is 150/min. An ECG shows a narrow complex tachycardia. Intravenous access is gained and 6mg of adenosine is given with no effect.
What is the most appropriate next step?
A.A Intravenous adenosine 12 mg***
B.A Intravenous adenosine 6mg
C.A Intravenous verapamil 2.5-5 mg
D.A Radio-frequency ablation
E.A Electrical cardioversion.