Answer 4

4.  Answer D is the correct answer.  This patient has A-Fib with RVR.  Defibrillation is reserved for Ventricular Tachycardia, Ventricular Fibrillation, or unstable A-Fib.  This is a narrow complex tachycardia that is irregular.  Adenosine or Labetolol would be appropriate for supraventricular tachycardia or sinus tachycardia.