A 36-year-old man presents with the sensation of a racing heart. His blood pressure is 110/70, respiratory rate 14/min, and O2 saturation 98%. ECG is shown. Carotid massage and Valsalva maneuver do not improve the heart rate. Which of the following is the initial therapy of choice?

Adenosine, with its excellent safety profile and extremely short half-life, is the drug of choice for supraventricular tachycardia (SVT). The initial dose is 6 mg. A dose of 12 mg can be given a few minutes later if necessary. Verapamil is the next alternative; if the initial dose of 2.5 to 5 mg does not yield conversion, one or two additional boluses 10 minutes apart can be used as long as systolic BP stays above 100. Diltiazem and digoxin may be useful in rate control and conversion but have a slower onset of action. Electrical cardioversion is reserved for hemodynamically unstable patients. Lidocaine is occasionally used in ventricular (not supraventricular) arrhythmias.