⚡ Chapter 48: Supraventricular Tachycardia

Narrow QRS Tachycardia · Adenosine · Vagal Manoeuvres · AVNRT · AVRT · WPW Syndrome · Cardioversion

⚡ Supraventricular Tachycardia: Most Common Symptomatic Paediatric Arrhythmia

📊 Definition & Epidemiology
SVT = tachycardia originating above the ventricles. Heart rate: infants >220/min, older children >180/min. Most common in first 4 months, 8-10 years, and adolescence. Accounts for ~13% of paediatric arrhythmia ED visits.
🫀 Types of SVT
• AVRT (most common): accessory pathway (WPW) — delta wave on sinus ECG
• AVNRT: re-entry within AV node — P wave buried in QRS
• Atrial tachycardia (AT/MAT): automatic focus in atrium
• JET: AV dissociation
🔬 SVT vs Sinus Tachycardia
SVT: abrupt onset/offset, fixed HR, no P waves, no variability. Sinus: gradual onset, variable HR, normal P waves, rate varies with activity/fever.
💉 Acute Management (Haemodynamically Stable)
1. Vagal manoeuvres (ice to face, Valsalva)
2. Adenosine 0.1 mg/kg rapid IV push (max 6 mg) → flush
3. Second dose 0.2 mg/kg (max 12 mg)
4. Amiodarone or procainamide if refractory
⚠️ Unstable SVT (Hypotension, Poor Perfusion)
Immediate synchronised cardioversion: 0.5-1 J/kg. Increase to 2 J/kg if needed. Sedate if possible.
📋 WPW Syndrome
Delta wave (short PR, slurred QRS upstroke). Avoid digoxin and verapamil (risk of VF). Long-term: beta-blockers, flecainide, or ablation.
📌 Key Pearls: Adenosine half-life is 5-10 seconds — give as RAPID push with immediate saline flush. Failure to convert may be due to slow administration. Never give verapamil to infants <1 year (risk of cardiovascular collapse).

🩺 Step-by-Step: Management of Supraventricular Tachycardia

1
Assess haemodynamic status
Is the child stable? Look for: normal BP, adequate perfusion, normal mental status, no shock signs. If unstable → immediate synchronised cardioversion!
2
Unstable SVT → Synchronised cardioversion
Energy: 0.5-1 J/kg. Sedate if possible (ketamine, midazolam). Ensure synchronised mode (R wave). Increase to 2 J/kg if first shock fails.
3
Stable SVT → Vagal manoeuvres
• Infants: ice to face (diving reflex) — apply bag of ice water to upper face for 5-10 seconds
• Older children: Valsalva (blow through straw), cough, breath-holding
4
Failed vagal manoeuvres → Adenosine
• First dose: 0.1 mg/kg rapid IV push (max 6 mg)
• Immediately flush with 5-10 mL saline
• If no conversion in 1-2 min: second dose 0.2 mg/kg (max 12 mg)
5
Adenosine-refractory SVT → Second-line agents
• Amiodarone: 5 mg/kg IV over 20-60 min, then infusion 5-15 mcg/kg/min
• Procainamide: 15 mg/kg over 30-60 min
• Esmolol: 500 mcg/kg bolus then 50-200 mcg/kg/min infusion
6
Post-conversion evaluation
Obtain 12-lead ECG to check for delta wave (WPW), structural abnormalities. Echocardiogram to rule out congenital heart disease. Consider Holter monitor for intermittent SVT.
7
Long-term management
• Infrequent episodes: no chronic therapy, teach vagal manoeuvres
• Frequent/recurrent: beta-blockers (propranolol), flecainide, or referral for catheter ablation (curative)