What is the most appropriate medication to administer to a patient with supraventricular tachycardia (SVT) when vagal maneuvers are ineffective?

Adenosine is the Most Appropriate Medication

For an infant with supraventricular tachycardia (SVT) when vagal maneuvers fail, adenosine is the definitive first-line pharmacologic treatment. 1, 2

Why Adenosine is the Correct Choice

Adenosine is specifically recommended by the American Heart Association and ACC/AHA/HRS guidelines as the drug of choice for acute SVT termination after failed vagal maneuvers, with success rates of 90-95% in pediatric patients. 1, 2

Mechanism and Efficacy

• Adenosine briefly depresses AV node conduction, terminating reentrant tachycardias that involve the AV node (AVNRT and orthodromic AVRT) in 85-100% of cases 1, 3, 4
• The drug has an extremely short half-life of less than 10 seconds, making it exceptionally safe even if ineffective 3, 4
• Rapid onset of action occurs within 30 seconds of administration 3

Pediatric Dosing Protocol

• Initial dose: 0.05 mg/kg IV rapid bolus (for infants/neonates) 5
• Can be increased in increments of 0.05 mg/kg every 1-2 minutes up to maximum 0.25 mg/kg 5
• Must be given as rapid IV push followed immediately by 20 mL saline flush through a large proximal vein 1, 2
• A defibrillator should be readily available during administration 1, 2

Why NOT the Other Options

Diltiazem - Contraindicated in Infants

• Calcium channel blockers like diltiazem are not recommended for infants and young children due to risk of severe hypotension and cardiac arrest 1
• Only appropriate for stable narrow-complex tachycardias in adults when adenosine fails 1, 6

Esmolol - Second-Line Agent

• Beta blockers are second-line agents for pediatric SVT, used only when adenosine is ineffective or contraindicated 1
• Carries risks of hypotension, bradycardia, and precipitation of heart failure 1

Amiodarone - Not First-Line for SVT

• Amiodarone is indicated for atrial fibrillation or when other agents fail, not as initial therapy for regular narrow-complex SVT 1
• Has slower onset of action and more significant adverse effects including hypotension 1

Critical Safety Considerations

Monitoring Requirements

• Continuous ECG monitoring during and after administration 2, 5
• Monitor blood pressure, respiratory status, and capillary refill 5
• Watch for recurrence, which occurs commonly due to adenosine's short half-life 2, 7

Expected Transient Side Effects

• Flushing, dyspnea, chest discomfort occur in approximately 30% of patients but last less than 1 minute 1, 3, 4
• Transient sinus bradycardia and varying degrees of AV block may occur 5, 4
• These effects resolve spontaneously due to the ultra-short half-life 3, 4

Contraindications

• Asthma (risk of bronchospasm) 1, 2
• Second or third-degree AV block or sick sinus syndrome 2

Post-Conversion Management

If SVT recurs after successful adenosine conversion, repeat adenosine dosing or consider a longer-acting AV nodal blocking agent such as a beta blocker. 2, 7

• Monitor for at least 1-2 hours after successful conversion 7
• Recurrent episodes may require prophylactic antiarrhythmic therapy or cardiology referral 7
• If adenosine repeatedly fails, synchronized cardioversion should be performed 1