Situation: A 52-year-old woman with moderate rheumatic mitral stenosis is brought to the emergency room (ER) because of palpitations and shortness of breath that began 6 hours ago. The cardiac monitor shows atrial fibrillation with a ventricular rate of about 150/min. She has no known drug allergies. Her blood pressure is 80/50 mmHg, she is newly confused, and she reports chest discomfort. The provider is at the bedside. Which intervention should the nurse prepare for?

Hypotension, new confusion, and ischemic chest discomfort are signs of instability. A tachydysrhythmia with a pulse and signs of instability is treated with synchronized cardioversion, timed to the R wave, with sedation if possible. Drug therapy for rate or rhythm is reserved for stable clients.

Why synchronized cardioversion is the priority
This patient has atrial fibrillation with a rapid ventricular response, but the decision to intervene immediately is driven by the presence of hemodynamic instability. Her blood pressure of 80/50 mmHg, new-onset confusion, and ischemic chest discomfort are direct signs that the heart is no longer perfusing the brain and coronary arteries adequately. In unstable tachyarrhythmias with a palpable pulse, synchronized cardioversion is the definitive first-line treatment because it delivers a shock timed to the R wave, interrupting the reentrant circuit and restoring an organized rhythm without waiting for drug onset. The timing to the R wave is critical: it prevents the shock from landing on the vulnerable T wave, which could otherwise trigger ventricular fibrillation.

Key point! The presence of a pulse is what distinguishes the need for synchronized cardioversion from unsynchronized defibrillation. Unsynchronized defibrillation is reserved for pulseless arrest rhythms such as ventricular fibrillation or pulseless ventricular tachycardia.

Why the other options are incorrect
Unsynchronized defibrillation would be inappropriate because the patient has a pulse and a perfusing, albeit unstable, rhythm. Delivering a shock at a random point in the cardiac cycle in a patient with organized electrical activity risks inducing a lethal arrhythmia.

Adenosine is used for narrow-complex supraventricular tachycardias, particularly those involving the atrioventricular node as part of a reentrant circuit, such as AV nodal reentrant tachycardia. Atrial fibrillation is not terminated by adenosine, and giving it would only cause a transient AV block without addressing the underlying atrial rhythm. Furthermore, adenosine is never appropriate for an unstable patient when immediate electrical therapy is indicated.

Diltiazem, a non-dihydropyridine calcium channel blocker, slows conduction through the AV node and can effectively reduce the ventricular rate in stable atrial fibrillation. However, rate-control medications are reserved for patients who are hemodynamically stable. In this patient with hypotension and end-organ hypoperfusion, the negative inotropic and vasodilating effects of diltiazem could further drop blood pressure and worsen shock. The unstable patient needs rhythm restoration, not gradual rate slowing.

Sedation during synchronized cardioversion
The question specifies that the provider is at the bedside and asks what the nurse should prepare for. The correct answer includes “with sedation if time allows.” This reflects the clinical reality that synchronized cardioversion is painful, and procedural sedation should be given whenever the patient’s condition permits a brief delay for medication administration. However, if the patient is deteriorating so rapidly that any delay would be dangerous, cardioversion may proceed without sedation. The nurse’s role includes preparing the defibrillator, ensuring the sync mode is activated, having emergency airway equipment and sedation medications ready, and placing conductive pads in the correct positions.

Rheumatic mitral stenosis and atrial fibrillation
This patient’s underlying rheumatic mitral stenosis is directly relevant to why she developed atrial fibrillation. Chronic mitral stenosis leads to elevated left atrial pressure, progressive left atrial dilation, and structural remodeling of the atrial myocardium. These changes create the substrate for atrial fibrillation. When atrial fibrillation develops, the loss of effective atrial contraction is especially dangerous in mitral stenosis because left ventricular filling is already dependent on the atrial “kick” to push blood across the narrowed mitral valve. The sudden loss of that contribution, combined with a rapid ventricular rate that shortens diastolic filling time, can precipitate acute pulmonary congestion and low cardiac output. This explains why a patient with moderate mitral stenosis can deteriorate so quickly when atrial fibrillation begins.

Comparison	Synchronized cardioversion	Unsynchronized defibrillation	Rate control (diltiazem)
Indication	Unstable tachyarrhythmia with a pulse (e.g., AF, SVT, VT with pulse)	Pulseless VT or ventricular fibrillation	Stable atrial fibrillation with rapid ventricular rate
Shock timing	Delivered on the R wave to avoid the T wave	Delivered at any point in the cycle	No shock; medication slows AV node conduction
Hemodynamic status	Unstable but perfusing	Cardiac arrest, no perfusion	Stable, adequate perfusion
Risk if used incorrectly	May fail to convert if sync mode not activated	May induce VF if used on a patient with a pulse	May worsen hypotension and shock in unstable patients

Watch out! Before delivering a synchronized shock, the nurse must verify that the “sync” button is activated and that the monitor is detecting each R wave. If the sync mode is off, the shock may fire randomly and cause ventricular fibrillation. After each attempt, the sync mode often resets, so it must be reactivated before subsequent shocks.

Clinical priorities in the emergency setting
The immediate nursing priorities are to recognize the instability pattern, call for the provider and emergency equipment, apply oxygen if hypoxemic, obtain IV access, and prepare the defibrillator for synchronized cardioversion. Continuous monitoring of blood pressure, mental status, and oxygen saturation is essential because these parameters determine whether the intervention is working. The underlying rheumatic mitral stenosis will still require long-term management, including anticoagulation for atrial fibrillation, possible rate or rhythm control once stable, and evaluation for valvular intervention. However, those concerns are secondary to the immediate need to restore a perfusing rhythm in the emergency department.