What is the recommended management plan for a patient with severe symptoms of supraventricular tachycardia (SVT), including hypotension, tachycardia, and hypoxia?

Management of Hemodynamically Unstable Supraventricular Tachycardia

In this 30-year-old woman presenting with narrow-complex SVT and severe hemodynamic instability (BP 64/40, HR 190, O2 sat 89%), synchronized cardioversion should be performed immediately, though a rapid trial of adenosine may be attempted first if it does not delay definitive electrical therapy. 1

Immediate Management Algorithm

Step 1: Recognize Hemodynamic Instability

This patient meets multiple criteria for unstable SVT 1:

• Hypotension (BP 64/40 mmHg - significantly below normal)
• Hypoxia (O2 sat 89% on room air)
• Extreme tachycardia (HR 190 bpm)
• Signs of shock (diaphoresis, acute distress)

Step 2: Choose Between Adenosine Trial vs Immediate Cardioversion

The 2015 ACC/AHA/HRS guidelines explicitly state that synchronized cardioversion should be performed for hemodynamically unstable patients with SVT when vagal maneuvers or adenosine are ineffective or not feasible. 1 However, the guidelines also note that adenosine may be considered first if the tachycardia is regular and has a narrow QRS complex, even in unstable patients. 1

Key decision point: If adenosine can be administered within seconds without delaying cardioversion setup, it may be attempted. However, cardioversion equipment must be immediately available. 1

Step 3: If Attempting Adenosine First

• Adenosine 6 mg rapid IV push through proximal IV line followed by saline flush 1
• If unsuccessful after 1-2 minutes, give 12 mg rapid IV push 1
• Success rate is 90-95% for orthodromic AVRT and AVNRT 1

Critical caveat: The patient's history of symptoms triggered by alcohol raises concern for possible accessory pathway (WPW syndrome). If adenosine precipitates atrial fibrillation in a patient with WPW, it could cause rapid ventricular conduction and ventricular fibrillation. 1 Therefore, cardioversion equipment must be immediately ready. 1

Step 4: Synchronized Cardioversion (Definitive Treatment)

Synchronized cardioversion is the Class I, Level B-NR recommendation for hemodynamically unstable SVT. 1

• Energy level: Start with 50-100 J synchronized 1
• Sedation: If patient is conscious (which she is), provide procedural sedation before cardioversion 1
• Success rate: Cardioversion successfully restored sinus rhythm in 100% of hemodynamically unstable SVT patients in prehospital studies 1

Why Other Options Are Incorrect

Cold Water Facial Immersion

While vagal maneuvers including facial immersion in cold water are Class I recommendations for hemodynamically STABLE patients 1, they should not delay definitive therapy in unstable patients. 1 In this severely hypotensive, hypoxic patient, vagal maneuvers would waste critical time.

IV Metoprolol

Beta blockers are contraindicated in this scenario for multiple reasons 1:

• Patient is severely hypotensive (BP 64/40) - beta blockers can worsen hypotension 1
• Beta blockers are reasonable only for hemodynamically stable patients 1
• The guidelines specifically state these agents should be used "only in hemodynamically stable patients" 1

IV Procainamide

Procainamide is indicated for pre-excited atrial fibrillation (wide-complex irregular tachycardia), not regular narrow-complex SVT. 1 This patient has narrow QRS tachycardia without evidence of pre-excitation. Additionally, procainamide would be too slow-acting for a patient in shock. 1

Critical Clinical Pearls

Diagnostic consideration: The narrow QRS complex confirms this is supraventricular in origin (likely AVNRT or orthodromic AVRT). 1 The alcohol trigger suggests possible accessory pathway involvement. 1

Common pitfall: Do not use calcium channel blockers (diltiazem, verapamil) or beta blockers in hemodynamically unstable patients, as they can precipitate cardiovascular collapse. 1 These are reserved for stable patients only.

Safety consideration: Recent evidence from a 2025 multicentre study suggests that in unstable SVT patients, adenosine may be attempted as a safe first-line therapy before cardioversion, potentially reducing sedation-related risks, but electrical cardioversion had superior conversion rates (OR 2.41,95% CI: 1.01-7.14). 2 However, this should not delay cardioversion if adenosine is not immediately available or fails rapidly.

Post-conversion monitoring: After successful cardioversion, monitor for recurrence and consider antiarrhythmic prophylaxis if tachycardia reinitiates. 1 Definitive management with catheter ablation should be discussed, as it has 94-98% success rates. 3