The patient's heart rate is 165 beats per minute and his cardiac monitor shows a rapid rate with narrow QRS complexes; the waves cannot be seen, but the rhythm is regular. The patient is symptomatic so the nurse prepares the patient for:

Rationale: A. Administration of beta-blockers is incorrect as the immediate priority. Beta-blockers are used to slow heart rate in stable supraventricular tachycardia (SVT) but are not the first choice in a symptomatic patient who may be unstable (e.g., hypotension, altered mental status, chest pain, or signs of shock). B. Administration of atropine is incorrect because atropine is used to treat bradycardia, not tachycardia. The patient’s heart rate is extremely high (165 bpm), so atropine would worsen the condition. C. Transcutaneous pacemaker insertion is incorrect because pacemakers are used to treat bradyarrhythmias or heart block, not tachyarrhythmias. D. Emergent cardioversion is correct because the patient is symptomatic with a narrow-complex tachycardia, likely supraventricular tachycardia (SVT). Current ACLS guidelines recommend synchronized cardioversion for unstable SVT to rapidly restore sinus rhythm. Symptoms such as dizziness, hypotension, chest pain, or altered mental status indicate that the patient is hemodynamically unstable, necessitating urgent cardioversion.