Supraventricular Tachycardia (SVT)

Presentation & Diagnosis

• Most common neonatal arrhythmia. Heart rate sustained consistently > 220-250 bpm.
• ECG characteristics: Absolutely narrow QRS complex (<0.08 sec), absent or abnormal P waves, strictly regular R-R intervals.
• Clinical signs: Poor feeding, pallor, irritability. If sustained >24 hours, leads to fatal congestive heart failure and cardiogenic shock.
• Must perform a full 12-lead ECG during tachycardia AND after conversion to rule out Wolff-Parkinson-White (WPW) (delta waves, short PR).

Acute Management Algorithm

• Hemodynamically UNSTABLE (shock, extremely poor perfusion): Immediate synchronized cardioversion at 0.5 - 1.0 Joules/kg. If fails, increase to 2 Joules/kg.
• Hemodynamically STABLE: Attempt vagal maneuvers exclusively (application of ice bag strictly to the face/forehead over nose ensuring airway patency for maximum 15-20 seconds).
• Adenosine push: 0.1 mg/kg rapid IV push strictly targeting a central or large proximal vein (closest to heart). Must absolutely be followed instantly by a rapid 3-5 mL flush of normal saline.
• If no conversion, double Adenosine dose to 0.2 mg/kg (maximum 0.3 mg/kg or 12 mg total).
• Continuous visual observation of the ECG monitor during pushing to identify the brief period of complete asystole or reveal underlying atrial flutter waves.

Maintenance Pharmacotherapy

• Consult Pediatric Electrophysiology (EP).
• First-line prophylactic therapy: Propranolol 1-4 mg/kg/day divided Q6H.
• Alternative/WPW specific: Sotalol or Amiodarone (beware profound thyroid toxicity with Amiodarone).
• Digoxin: Contraindicated strictly if WPW pattern is suspected due to risk of accelerated conduction down the accessory pathway leading to V-Fib.
• Continuous telemetry monitoring mandated for 48 hours post-conversion.

Diagnostic & Management Algorithm

• SVT Narrow Complex Rhythm Conversion: [START] HR > 220, no p-waves -> [DECISION] Stable? -> [YES] Ice to face (Vagal) 15 secs -> [DECISION] Still SVT? -> [YES] Adenosine 0.1 mg/kg rapid IV push

References

1. Brugada J, Blom N, Sarquella-Brugada G, et al. Pharmacological and non-pharmacological therapy for arrhythmias in the pediatric population. Europace.