THE ANSWER

Perform an initial assessment to confirm that airway, breathing and circulation are adequate.  The patient meets the criteria for unstable narrow complex tachycardia and needs to be treated.  You should try to determine the time of onset of the atrial fibrillation.  If the atrial fib has been present for 48 hours or more the patient is at increased risk for atrial thrombus and that must be taken into consideration before cardioverting.  The patient tells you that his pulse was regular until about an hour before your arrival.  You should sedate and cardiovert the patient.