Question

An infant presents to the emergency department with respiratory distress and a heart rate of 240/min. On examination, the patient is in shock. ECG shows a narrow-complex tachycardia. What is the next step in management?

• A. Adenosine
• B. Defibrillation
• C. Cardioversion
• D. Lignocaine

Hint:

PALS Algorithm for Pediatric SVT:
- Stable Patient: Vagal maneuvers (Ice bag to face) $\rightarrow$ Rapid IV Adenosine ($0.1\text{ mg/kg}$, max $6\text{ mg}$; then $0.2\text{ mg/kg}$, max $12\text{ mg}$).
- Unstable Patient (Shock, poor perfusion, altered mental status): Immediate Synchronized Cardioversion ($0.5\text{--}1\text{ J/kg}$, titrate to $2\text{ J/kg}$).

Answer 1

The Correct Option is C

Concept:
Supraventricular Tachycardia (SVT) is the most common pathological tachyarrhythmia encountered in infants and children, typically presenting with sudden-onset narrow QRS complex tachycardia with absent or abnormal P waves and fixed R-R intervals at rates $> 220\text{ beats/min}$ in infants ($> 180\text{ beats/min}$ in older children).
Explanation:
• According to Pediatric Advanced Life Support (PALS) resuscitation guidelines, the initial management algorithm for SVT depends directly on hemodynamic stability:
- Hemodynamically Unstable (Signs of Shock Altered Sensorium Hypotension Poor Perfusion): Immediate synchronized electrical cardioversion is the mandatory first-line therapy.
- Hemodynamically Stable: Vagal maneuvers (such as application of an ice-bag to the face for 15--20 seconds) followed by rapid IV push of Adenosine.

• Because this infant presents with overt signs of shock and hemodynamic collapse, attempting vagal maneuvers or delaying for vascular access/adenosine administration can lead to cardiac arrest; therefore, prompt synchronized cardioversion is indicated.

• The initial recommended dose for synchronized cardioversion in unstable pediatric SVT is 0.5 to 1 J/kg; if unsuccessful, the energy can be increased to 2 J/kg.

• Defibrillation (unsynchronized shock) is strictly used for pulseless arrest rhythms (Ventricular Fibrillation and Pulseless Ventricular Tachycardia) and should not be used in narrow-complex tachycardia with a pulse, as it risks triggering ventricular fibrillation (R-on-T phenomenon).

• Lignocaine (Lidocaine) is an antiarrhythmic used for ventricular arrhythmias, not for supraventricular tachycardia.
Final Answer:
In a hemodynamically unstable infant with SVT and shock, immediate synchronized electrical cardioversion is the definitive next step in management.