What is the preferred treatment for Supraventricular Tachycardia (SVT), adenosine or amiodarone?

Adenosine is the Preferred First-Line Treatment for SVT

Adenosine is recommended as the first-line pharmacological agent for acute treatment of hemodynamically stable supraventricular tachycardia, with amiodarone reserved only as a last-resort option when other therapies fail or are contraindicated. 1

Treatment Algorithm for SVT

Hemodynamically Stable Patients

Step 1: Vagal Maneuvers

• Perform Valsalva maneuver (bearing down against closed glottis for 10-30 seconds at 30-40 mmHg pressure) or carotid sinus massage (5-10 seconds after confirming no bruit) as immediate first intervention 1
• Success rate approximately 28% when switching between techniques 1

Step 2: Adenosine (Class I Recommendation)

• Adenosine terminates approximately 95% of AVNRT cases and 78-96% of SVT overall 1, 2
• Initial dose: 6 mg rapid IV push via large proximal vein, followed immediately by 20 mL saline flush 2
• If no conversion within 1-2 minutes: give 12 mg IV push 2
• May repeat 12 mg dose once more if needed 2
• Continuous ECG recording during administration is essential for diagnostic and therapeutic assessment 2

Step 3: Alternative AV Nodal Blockers (Class IIa Recommendation)

• If adenosine fails or recurrence occurs: intravenous diltiazem, verapamil, or beta-blockers 1
• These agents show 64-98% conversion rates but require slower infusion (up to 20 minutes) to minimize hypotension 1
• Critical contraindications: Do not use in VT, pre-excited atrial fibrillation, or suspected systolic heart failure 1

Step 4: Synchronized Cardioversion

• Indicated when pharmacological therapy fails or is contraindicated in stable patients 1
• Success rate 80-98% for SVT termination 1

Hemodynamically Unstable Patients

Immediate synchronized cardioversion is indicated for SVT causing hypotension, altered mental status, shock, chest pain, or acute heart failure 1

• However, adenosine should still be considered first if the tachycardia is regular with narrow QRS complex, even in unstable patients 1, 2

Amiodarone's Limited Role in SVT

Amiodarone receives only a Class IIb recommendation (lowest level) for SVT management 1

When Amiodarone May Be Considered:

• Only after adenosine, calcium channel blockers, and beta-blockers have failed or are contraindicated 1
• In patients with reduced ventricular function or heart failure where other agents are unsafe 1
• For focal atrial tachycardia when other therapies are ineffective 1

Critical Limitations of Amiodarone:

• Significantly higher risk profile: In pediatric studies, 71% experienced cardiovascular side effects (dose-related) 1
• Rare but serious complications include bradycardia, hypotension, cardiovascular collapse, and polymorphic VT 1
• Long-term toxicity concerns (pulmonary, thyroid) even with short-term IV use 1
• Slower onset of action compared to adenosine's immediate effect 1

Special Populations

Pregnancy

• Adenosine is safe and recommended as first-line treatment (Class I) 1, 2
• Amiodarone receives only Class IIb recommendation for potentially life-threatening SVT when other therapies fail 1

Pediatric Patients

• Adenosine remains first-line with success rates matching adults 1, 3
• Amiodarone shows better results when administered within 48 hours of diagnosis but carries significant side effect burden 3

Adenosine Dosing Adjustments

Increase dose for patients taking theophylline, caffeine, or theobromine 2

Decrease initial dose to 3 mg for: 2

• Patients on dipyridamole or carbamazepine
• Heart transplant recipients
• Central venous administration (requires 50% dose reduction due to higher bioavailability) 4

Contraindications: Second or third-degree AV block, sick sinus syndrome, asthma (risk of bronchospasm) 2

Common Pitfalls to Avoid

• Never use calcium channel blockers or amiodarone if VT or pre-excited AF is possible - can cause ventricular fibrillation or hemodynamic collapse 1
• Ensure rapid IV push technique with immediate saline flush for adenosine - slow administration reduces efficacy 2
• Have defibrillator available when administering adenosine in patients with possible Wolff-Parkinson-White syndrome 2
• Adenosine's transient side effects (flushing, dyspnea, chest discomfort) last <60 seconds and should not deter use 2, 5

Evidence Quality

The recommendation for adenosine over amiodarone is based on consistent Class I evidence from the 2015 ACC/AHA/HRS guidelines 1, with adenosine demonstrating superior safety profile, faster onset, and equivalent or superior efficacy (93-95% success rate) compared to all alternatives 1, 5. Amiodarone's relegation to Class IIb status reflects limited evidence for SVT specifically and concerning safety data 1.