What is the role of adenosine in treating a pediatric patient with unstable supraventricular tachycardia (SVT)?

Role of Adenosine in Unstable Pediatric SVT

Adenosine should be considered as first-line pharmacologic therapy for unstable pediatric SVT with regular narrow-complex tachycardia, but synchronized cardioversion remains the definitive treatment if the patient is truly hemodynamically unstable or if adenosine fails. 1, 2

Critical Initial Decision Point

The key distinction is whether the patient has regular narrow-complex SVT versus wide-complex tachycardia or irregular rhythms:

• For regular narrow-complex SVT (even if unstable): Adenosine can be attempted first if IV access is already established and the rhythm is clearly supraventricular 1, 2
• For wide-complex tachycardia: Never assume it is SVT—treat as ventricular tachycardia with synchronized cardioversion (0.5-1 J/kg) rather than adenosine 2
• For truly unstable patients: Synchronized cardioversion is preferred and should not be delayed for pharmacologic interventions if the patient has severe hypotension, poor perfusion, or altered mental status 1, 3

Adenosine Dosing Protocol for Pediatric SVT

The American Academy of Pediatrics recommends higher starting doses in children compared to adults:

• Initial dose: 0.1 mg/kg (100 mcg/kg) rapid IV bolus 1
• Second dose: 0.2 mg/kg (200 mcg/kg) if first dose fails 1
• Maximum dose: 0.3 mg/kg (300 mcg/kg) 1
• Administration technique: Use large proximal vein (antecubital preferred) with the most rapid IV push possible, followed immediately by 5-10 mL rapid saline flush 1, 4

Important Caveat About Age

Infants respond poorly to adenosine compared to older children:

• Only 1 of 17 episodes in infants responded to the first adenosine dose in one study 3
• Response to first dose increases proportionally with age (OR 1.13 per year) 3
• Adenosine-refractory SVT is significantly more common in infants versus older children 3

Expected Success Rates

Overall cardioversion success is 72-88% for all SVT types, with 79-96% success for AV node-dependent SVT 1, 4:

• First dose effective in approximately 56% of episodes 3
• Second dose effective in 50% of remaining episodes 3
• Approximately 15% will have refractory SVT requiring alternative therapy 3

Management of Adenosine-Refractory or Failed Cases

If adenosine fails after appropriate dosing:

• Procainamide has higher success rates than amiodarone for refractory pediatric SVT with equal adverse effects 1
• Synchronized cardioversion is the definitive treatment for unstable patients or when pharmacologic therapy fails 1
• Continuous ECG recording during adenosine administration helps distinguish true failure from transient termination with immediate reinitiation 4, 5

Critical Safety Considerations

Common pitfalls to avoid:

• Never use verapamil in infants due to multiple reports of cardiovascular collapse and death 1, 2
• Ensure proper administration technique—improper delivery is a common cause of apparent "adenosine failure" due to the drug's extremely short half-life 5
• Have defibrillator available when administering adenosine if Wolff-Parkinson-White syndrome is a consideration, as adenosine can precipitate atrial fibrillation with rapid ventricular rates 4
• Adenosine should not be given to patients with asthma due to risk of bronchospasm 4

Post-Conversion Monitoring

After successful conversion, immediate recurrence is common:

• Monitor continuously for recurrence, as patients commonly experience premature complexes that trigger recurrent SVT within seconds to minutes 4
• Early re-initiation of SVT occurs in approximately 25% of episodes 6
• Consider prophylactic AV nodal blockade (diltiazem or β-blocker) in patients with immediate recurrence 4

Real-World Clinical Context

In actual practice, synchronized cardioversion is rarely performed for acute pediatric SVT 3:

• Medical management with adenosine and various antiarrhythmics before cardioversion has a role in a subset of unstable patients 3
• The decision to attempt adenosine versus immediate cardioversion depends on the degree of instability and whether IV access is already established 1, 2
• If the patient is profoundly unstable (severe shock, unresponsive), do not delay cardioversion for adenosine administration 2