Unstable Supraventricular Tachycardia
A 9-month-old infant has 6 hours of poor feeding and lethargy. Heart rate is 250 beats/min and does not vary with stimulation, blood pressure is 50/30 mm Hg, and the extremities are mottled and cool. The rhythm strip shows a regular narrow complex tachycardia. Peripheral intravenous access has failed twice and no intraosseous access is established. Which of the following is the most appropriate immediate intervention?
- A.Application of ice to the face
- B.Carotid sinus massage
- C.Intravenous adenosine 0.1 mg/kg
- D.Synchronized cardioversion at 0.5 to 1 J/kgCorrect
Explanation
This infant has supraventricular tachycardia with hypotension, prolonged capillary refill, mottling, and hepatomegaly, which constitute hemodynamic instability with cardiogenic shock, so immediate synchronized cardioversion at 0.5 to 1 J/kg is indicated and should be escalated to 2 J/kg if the first shock fails. Synchronization to the R wave is essential to avoid delivering a shock during the vulnerable period of repolarization, which could induce ventricular fibrillation, and sedation should be given if it does not delay the shock in a collapsing child. Vagal maneuvers such as ice to the face are appropriate only in a stable infant and must never delay electrical therapy in shock, although a single brief attempt may be made while the defibrillator is being prepared. Carotid sinus massage is not used in children. Adenosine is a reasonable alternative to cardioversion in an unstable child only when reliable vascular access is already in place, but here access has failed, so waiting to obtain it would waste critical time. If access is obtained quickly, adenosine must be delivered as a rapid push into a large proximal vein with an immediate saline flush because its half-life is under 10 seconds. Verapamil is contraindicated in infants younger than 1 year because it can cause profound hypotension and cardiac arrest. After conversion, obtain a 12 lead electrocardiogram to look for preexcitation and an echocardiogram to assess ventricular function and exclude structural disease such as Ebstein anomaly.
Why each option
- A.
- Ice to the face is a vagal maneuver for stable infants and must not delay electrical therapy in a shocked child.
- B.
- Carotid sinus massage is not recommended in children and is ineffective in this setting.
- C.
- Adenosine is acceptable in an unstable child only if vascular access already exists; access has failed here, so it would delay treatment.
- D.
- Correct. Hemodynamically unstable supraventricular tachycardia requires immediate synchronized cardioversion at 0.5 to 1 J/kg.
Reference: AHA Pediatric Advanced Life Support Guidelines, 2020
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