What is the best immediate treatment for a hemodynamically unstable patient with paroxysmal supraventricular tachycardia?

Best Treatment for PSVT with Shock

Immediate synchronized cardioversion is the definitive treatment for paroxysmal supraventricular tachycardia presenting with shock or hemodynamic instability—do not attempt vagal maneuvers or pharmacologic therapy first. 1, 2, 3

Defining Hemodynamic Instability (When to Cardiovert Immediately)

Proceed directly to synchronized cardioversion without any delay if the patient exhibits any of the following:

• Hypotension (systolic BP <90 mmHg) 3
• Altered mental status or syncope 1, 3
• Signs of shock (cold extremities, poor perfusion, oliguria) 1, 3
• Chest pain with ST-segment changes (acute myocardial ischemia) 3
• Acute heart failure or pulmonary edema 1, 3

Immediate Management Algorithm

Step 1: Synchronized Cardioversion (First-Line for Shock)

Synchronized cardioversion achieves near-100% termination of PSVT in hemodynamically unstable patients and must be performed without attempting vagal maneuvers or drug therapy. 1, 3

• Initial energy: 50–100 joules 3
• Provide procedural sedation if the patient is conscious 3
• Have defibrillator and resuscitation equipment immediately available 3

Step 2: Exception—Single Adenosine Dose (Only If Narrow-Complex & Not in Profound Shock)

If the patient has a regular narrow-complex tachycardia and is unstable but not in profound shock (e.g., systolic BP 85–90 mmHg, alert), one rapid adenosine dose may be attempted while preparing for cardioversion. 2, 3

• Adenosine 6 mg rapid IV push through a proximal vein, followed immediately by 20 mL saline flush 2, 3
• Success rate: 90–95% for AVNRT and orthodromic AVRT 2, 3
• Critical safety requirement: Cardioversion equipment must be at bedside because adenosine can precipitate atrial fibrillation with rapid ventricular conduction, potentially causing ventricular fibrillation 3
• Do not give a second adenosine dose—if the first fails, proceed immediately to cardioversion 3

Absolute Contraindications in Unstable PSVT

Never administer the following in hemodynamically unstable patients:

• Calcium channel blockers (diltiazem, verapamil)—can precipitate cardiovascular collapse 1, 3
• Beta-blockers (metoprolol, esmolol)—worsen hypotension 3
• Digoxin—too slow-acting and dangerous in pre-excitation 3

Special Consideration: Pre-Excited Atrial Fibrillation (Wolff-Parkinson-White)

If the ECG shows irregular wide-complex tachycardia (pre-excited AF), proceed directly to synchronized cardioversion without adenosine. 1, 3

• Do not give adenosine, calcium channel blockers, beta-blockers, or digoxin—these enhance accessory pathway conduction and can precipitate ventricular fibrillation 3
• If stable enough for pharmacologic therapy (rare in shock), use IV procainamide or ibutilide 1

Post-Cardioversion Management

Anticipate immediate recurrence after successful cardioversion:

• Monitor continuously for premature atrial or ventricular complexes that can reinitiate tachycardia within seconds 3
• Have antiarrhythmic drugs ready (e.g., longer-acting AV-nodal blocker such as diltiazem or metoprolol) to prevent acute reinitiation if recurrence occurs 1, 3

Common Pitfalls to Avoid

• Do not delay cardioversion to attempt vagal maneuvers or multiple drug trials in a patient with shock 1, 3
• Do not give calcium channel blockers or beta-blockers in unstable patients—they cause cardiovascular collapse 1, 3
• Do not assume all narrow-complex tachycardias are safe for adenosine—if pre-excitation is present and AF develops, adenosine can be lethal 3
• Do not give adenosine without immediate cardioversion capability at bedside 3

Summary of Evidence Strength

The recommendation for immediate cardioversion in hemodynamically unstable PSVT is a Class I, Level B recommendation from the American College of Cardiology/American Heart Association/Heart Rhythm Society guidelines, with near-100% success rates in restoring sinus rhythm. 1, 3 The option to attempt a single adenosine dose in less-profound instability (regular narrow-complex tachycardia) is supported by the same guidelines but requires immediate cardioversion readiness. 2, 3