What is the management approach for unstable supraventricular tachycardia (SVT) in pediatric patients?

Management of Unstable Supraventricular Tachycardia in Children

For hemodynamically unstable pediatric patients with SVT, proceed immediately to synchronized cardioversion without attempting vagal maneuvers or pharmacologic therapy first. 1

Immediate Assessment and Stabilization

Identify hemodynamic instability by looking for any of the following signs 1:

• Hypotension or signs of shock
• Altered mental status
• Poor perfusion (prolonged capillary refill, cool extremities)
• Respiratory compromise
• Chest pain (in older children)
• Acute heart failure symptoms

While assessing, simultaneously 1:

• Maintain patent airway and assist breathing as necessary
• Administer high-flow oxygen
• Attach cardiac monitor/defibrillator
• Establish IV or IO access (but do not delay cardioversion for this)
• Obtain 12-lead ECG if immediately available, but do not delay therapy 1

Primary Treatment: Synchronized Cardioversion

Synchronized cardioversion is the definitive treatment for unstable SVT in children and achieves essentially 100% conversion rates. 1

Energy Dosing

• Initial energy: 0.5-1 J/kg 1
• If unsuccessful, increase to 2 J/kg for subsequent attempts 1
• Ensure adequate sedation/anesthesia if time permits and patient condition allows 1

Critical Technical Points

• Use synchronized mode to avoid delivering shock during vulnerable period of cardiac cycle 1
• Have resuscitation equipment immediately available 1
• Be prepared for atrial or ventricular premature complexes immediately post-cardioversion that may reinitiate tachycardia 1

When Cardioversion Is Delayed or Unavailable

If synchronized cardioversion equipment is temporarily unavailable or IV/IO access is already established, adenosine may be attempted as a bridge but should not delay definitive electrical therapy 1:

Adenosine Dosing in Children

• First dose: 0.1 mg/kg rapid IV/IO bolus (maximum 6 mg) 1
• Second dose: 0.2 mg/kg rapid bolus (maximum 12 mg) 1
• Must be given as rapid push through proximal/large vein followed immediately by saline flush 1
• Success rate is lower in infants (only 6% responded to first dose in one study) compared to older children 2

Important caveat: Adenosine effectiveness decreases with younger age, with infants showing significantly reduced response rates and higher rates of refractory SVT compared to older children. 2

Alternative Pharmacologic Agents (If Cardioversion Unavailable)

If adenosine fails and cardioversion remains unavailable 1:

• Amiodarone 5 mg/kg IV/IO over 20-60 minutes 1, 3
• Procainamide 15 mg/kg IV/IO over 30-60 minutes 1
• Do not routinely administer amiodarone and procainamide together 1

Critical Pitfalls to Avoid

Never delay cardioversion for vagal maneuvers in unstable patients. The AHA explicitly states that vagal maneuvers should only be attempted "unless the patient is hemodynamically unstable or the procedure will unduly delay chemical or electric cardioversion." 1

Do not use AV nodal blocking agents (adenosine, diltiazem, verapamil, beta-blockers) if there is any possibility of pre-excited atrial fibrillation (irregular wide-complex tachycardia), as these can precipitate ventricular fibrillation. 1, 4, 5 In unstable patients with suspected pre-excited AF, proceed directly to cardioversion. 1, 4

Avoid assuming all pediatric SVT will respond to adenosine. Approximately 15% of pediatric SVT cases are adenosine-refractory, with significantly higher rates in infants. 2 This reinforces the importance of having cardioversion equipment immediately available.

Post-Conversion Management

After successful cardioversion 1:

• Monitor closely for reinitiation of tachycardia from post-conversion premature beats
• Consider antiarrhythmic medication to prevent acute recurrence
• Search for and treat underlying triggers (fever, dehydration, medications)
• Arrange urgent cardiology consultation for ongoing management and consideration of catheter ablation 1

Special Consideration: Wide-Complex Tachycardia

If the QRS duration is >0.09 seconds (wide-complex), treat as ventricular tachycardia until proven otherwise in an unstable patient. 1 Proceed immediately to synchronized cardioversion without attempting adenosine, as wide-complex tachycardia may represent ventricular tachycardia or pre-excited AF, both of which require electrical cardioversion when unstable. 1, 6