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:

A. Beta-blockers, such as metoprolol or esmolol, are commonly used to slow the ventricular rate in certain tachyarrhythmias like atrial fibrillation or atrial flutter, especially when the patient is hemodynamically stable. However, in this scenario, the patient is symptomatic with a very high heart rate (165 bpm), which may indicate compromised cardiac output. Symptoms may include hypotension, chest pain, shortness of breath, or altered mental status. In unstable patients, beta-blockers are too slow to reverse the hemodynamic instability, making emergent cardioversion the appropriate first-line treatment. B. Pacemakers are indicated for bradycardia or high-grade heart block, not tachyarrhythmias. Using a pacemaker in a patient with supraventricular tachycardia (SVT) or other narrow complex tachycardias would not correct the rapid heart rate and may worsen patient condition. C. This patient demonstrates narrow complex tachycardia (likely SVT) that is regular and rapid, with symptoms indicating hemodynamic instability. According to ACLS (Advanced Cardiac Life Support) guidelines, synchronized electrical cardioversion is indicated for unstable tachyarrhythmias to restore sinus rhythm promptly. Synchronized cardioversion ensures the electrical shock is delivered during the R wave to avoid inducing ventricular fibrillation. Emergent cardioversion is prioritized over medications when a patient is unstable because it immediately restores cardiac output and perfusion. D. Atropine is an anticholinergic drug used primarily for bradycardia to increase heart rate by blocking vagal stimulation. Administering atropine to a patient with tachycardia would be inappropriate and could further increase heart rate, worsening myocardial oxygen demand and precipitating ischemia or hemodynamic collapse.