How should adenosine be administered (dose and technique) to a haemodynamically stable infant with narrow‑complex supraventricular tachycardia?

Adenosine Administration for SVT in Infants

For hemodynamically stable infants with narrow-complex SVT, administer adenosine as a rapid IV bolus starting at 0.1 mg/kg (maximum 6 mg), followed immediately by a rapid saline flush, using the most proximal IV site available. 1

Initial Dose and Administration Technique

• Initial dose: 0.1 mg/kg (maximum 6 mg for first dose) administered as a rapid IV push 1
• Critical technique requirement: Follow immediately with a rapid saline flush to ensure drug delivery to the heart before metabolism 1
• Use the most proximal IV site possible to minimize transit time and drug degradation 1
• Intraosseous (IO) administration is acceptable if IV access has not been achieved 1

Subsequent Dosing if Initial Dose Fails

• If no AV block occurs and no response within 30 seconds: Double the dose to 0.2 mg/kg (maximum 12 mg for second/subsequent doses) 1
• Follow with immediate rapid saline flush using the same technique 1
• May repeat escalating doses as needed 1

Essential Monitoring Requirements

• Continuous electrocardiographic monitoring must be employed during adenosine administration 1
• A defibrillator must be immediately available because adenosine may precipitate atrial fibrillation that conducts rapidly to the ventricle and can even cause ventricular fibrillation 2
• Monitor blood pressure, respiratory status, and capillary refill before, during, and after administration 3

Efficacy in Infants and Children

• Adenosine demonstrates approximately 90-95% effectiveness for terminating SVT in pediatric patients 4, 5
• Twenty-two studies in infants and children demonstrated effectiveness for both hemodynamically stable and unstable SVT 4, 5
• Termination typically occurs within 12-25 seconds of administration 6

Common Side Effects (Brief and Self-Limited)

• Side effects occur in approximately 30% of patients but are minor and brief (<1 minute duration) 2
• Transient complete AV block (less than 6 seconds) 7
• Sinus bradycardia (less than 40 seconds) 7
• Flushing, nausea, headache 7
• Nondistressing alterations in respiratory pattern 3
• Irritability 3
• Ventricular extrasystoles 7

Critical Contraindications

• Second- or third-degree AV block (unless functioning pacemaker present) 1
• Sick sinus syndrome or symptomatic bradycardia (unless functioning pacemaker present) 1
• Patients who have had a heart transplant 1

Important Technical Considerations

Stopcock Technique Limitation

• Avoid stopcock technique in infants <10 kg as it delivers significantly lower-than-intended doses (mean 0.08 mg/kg instead of 0.1 mg/kg in patients 2-9 kg) 8
• This underdosing may explain decreased response rates to first adenosine dose in infants 8

Alternative Single-Syringe Method

• Draw adenosine 0.2 mg/kg into a syringe containing 0.9% sodium chloride to total volume of 3 mL 9
• This single-syringe technique appears safe and effective in neonates and may deliver more reliable dosing 9, 10
• Single-syringe technique shows significantly increased termination rate at first dose compared to double-syringe technique 10

Reinitiation of SVT

• Reinitiation within 5 seconds occurs in approximately 11% of successfully terminated episodes 7
• Adenosine's extremely short half-life (0.6-10 seconds) means it will not prevent SVT recurrence 3
• If reinitiation occurs, consider antiarrhythmic prophylaxis with other medications 2

Special Population: Preterm Infants

• Adenosine is safe and effective in preterm infants with SVT 6
• Same dosing protocol applies (0.05 mg/kg initial, escalating by 0.05 mg/kg increments) 6
• Termination achieved within 12-25 seconds in all studied preterm cases 6
• One case showed temporary sinus node suppression followed by normal sinus rhythm resumption 6

If Adenosine Fails

• Synchronized cardioversion is recommended for hemodynamically unstable patients when adenosine is ineffective or not feasible 2
• For refractory stable SVT, procainamide may be considered (higher success rate than amiodarone in pediatric comparison studies) 4, 5
• Avoid verapamil in infants due to multiple reports of severe hypotension, bradycardia, heart block, hemodynamic collapse, and death 4, 5