Q. A 20-year-old male is brought to the emergency department after he was referred by the college nurse. The patient has been experienced dizzy spells and palpitations for the last hour. This is not the first time he experiences these symptoms. They are usually brought on by strong emotions and fatigue. However, symptoms dissipate with deep breaths or squatting. He has tried both but nothing has helped him this time. On examination, blood pressure is 65/40 mm Hg, heart rate 240/min, and respiration rate 20/min. Physical examination findings include diaphoresis and cold and clammy extremities. ECG shows a narrow complex tachycardia. What would be the most appropriate next step in managing this patient?