In a child who has collapsed with supraventricular tachycardia (hemodynamically unstable), what is the immediate management?

Immediate Management of Hemodynamically Unstable SVT in Children

Proceed immediately to synchronized cardioversion at 0.5-1 J/kg without attempting vagal maneuvers or adenosine—this is the definitive treatment for any collapsed child with SVT and achieves essentially 100% conversion rates. 1, 2

Critical First Steps

When a child has collapsed with SVT, hemodynamic instability is presumed until proven otherwise. The key distinguishing features of instability include:

• Signs of shock: poor perfusion, pallor, mottled skin, weak pulses 2
• Altered mental status or unresponsiveness 2, 3
• Hypotension for age 2
• Respiratory compromise or acute heart failure symptoms 2

While preparing for cardioversion, simultaneously:

• Maintain airway patency and assist breathing as needed 2
• Administer high-flow oxygen 2
• Attach cardiac monitor/defibrillator 2
• Establish IV or intraosseous access 2

Synchronized Cardioversion Protocol

Energy dosing:

• Initial dose: 0.5-1 J/kg 1, 2
• If unsuccessful, escalate to 2 J/kg 1, 2

Critical technical points:

• Use synchronized mode (not unsynchronized defibrillation) 1
• Provide sedation if time and patient condition permit, but never delay cardioversion for sedation in a truly unstable patient 1, 2
• Apply conductive gel to paddles/pads 3

Common Pitfalls to Avoid

Do not attempt vagal maneuvers in unstable patients. The 2015 AHA guidelines explicitly state that vagal stimulation should only be attempted "unless the patient is hemodynamically unstable or the procedure will unduly delay chemical or electric cardioversion." 1 In a collapsed child, this delay is unacceptable. 2

Do not give adenosine first in unstable SVT. While adenosine is 90-95% effective for stable SVT 1, 4, it causes a brief period of asystole and can worsen hemodynamic compromise in unstable patients. 4, 2 Multiple studies document that residents frequently make this error, with 90% administering adenosine inappropriately in unstable scenarios, causing median delays to cardioversion of 8.9 minutes. 3

Recognize that "collapsed" equals unstable. A common error is failure to assess perfusion and mental status, leading to misclassification of unstable patients as stable. 3 If the child has collapsed, assume instability and proceed directly to cardioversion. 2

If Cardioversion Fails or Is Unavailable

Only if synchronized cardioversion is unsuccessful or temporarily unavailable should you consider:

• Amiodarone 5 mg/kg IV/IO over 20-60 minutes 1, 2
• Procainamide 15 mg/kg IV/IO over 30-60 minutes 1, 2

Do not administer amiodarone and procainamide together. 2 Note that amiodarone causes cardiovascular side effects (bradycardia, hypotension, cardiovascular collapse) in 71% of pediatric patients. 1, 4

Special Consideration: Wide-Complex Tachycardia

If the QRS duration is >0.09 seconds in an unstable child, treat as ventricular tachycardia until proven otherwise and proceed immediately to synchronized cardioversion without attempting adenosine. 1, 2 Do not use AV nodal blocking agents if there is any possibility of pre-excited atrial fibrillation, as this can precipitate ventricular fibrillation. 4, 2

Post-Cardioversion Management

After successful conversion:

• Monitor continuously for recurrence from post-conversion premature beats 2
• Consider antiarrhythmic medication to prevent acute recurrence 2
• Search for and treat underlying triggers (hypoxia, electrolyte abnormalities, toxins) 2
• Arrange urgent cardiology consultation for ongoing management and consideration of catheter ablation 2

The evidence strongly supports that any delay in cardioversion for unstable pediatric SVT increases morbidity risk. The algorithm is straightforward: collapsed child + SVT = immediate synchronized cardioversion. 1, 2